Viruses and Langerhans cells - Nature

Immunology and Cell Biology (2010) 88, 416–423 & 2010 Australasian Society for Immunology Inc. All rights reserved 0818-9641/10 $32.00 www.nature.com/icb

REVIEW

Viruses and Langerhans cells Anthony L Cunningham1,2, Allison Abendroth2,3, Cheryl Jones1,2,4, Najla Nasr1,2 and Stuart Turville1,2 Langerhans cells (LCs) are the resident dendritic cells (DCs) of epidermis in human mucosal stratified squamous epithelium and the skin. A phenotypically similar DC has recently been discovered as a minor population in the murine dermis. In epidermis, LCs function as sentinel antigen-presenting cells that can capture invading viruses such as herpes simplex virus (HSV), varicella-zoster virus (VZV) and human immunodeficiency virus (HIV). This interaction between LCs and viruses results in highly variable responses, depending on the virus as discussed in this review. For example, HSV induces apoptosis in LCs but HIV does not. LCs seem to be the first in a complex chain of antigen presentation to T cells in lymph nodes for HSV and possibly VZV, or they transport virus to T cells, as described for HIV and maybe VZV. Together with epidermal keratinocytes they may also have a role in the initial innate immune response at the site of infection in the epidermis, although this is not fully known. The full spectrum of biological responses of LCs even to these viruses has yet to be understood and will require complementary studies in human LCs in vitro and in murine models in vivo. Immunology and Cell Biology (2010) 88, 416–423; doi:10.1038/icb.2010.42 Keywords: Langerhans cells; Herpes Simplex Virus; Herpes Zoster Virus; HIV

LANGERHANS CELL BIOLOGY/FUNCTION RELEVANT FOR VIRAL INFECTION OF EPITHELIA The resident dendritic cells (DCs) of stratified squamous epithelium in the anogenital and oropharyngeal mucosa can be subdivided into Langerhans cells (LCs) in the epidermis and interstitial or dermal DCs1 in the dermis. Interstitial DCs are the resident DCs of lamina propria in cuboidal and columnar epithelium. LCs form a tight network with each other and with the surrounding keratinocytes through the adhesion molecule E-cadherin. Thus, LCs are the sentinel DCs that interact with invading microorganisms in the vagina, ectocervix and male foreskin, usually through the pattern recognition receptors, C-type lectin receptors and Toll-like receptors (TLRs). After these interactions they produce effector cytokines and can initiate or restimulate activation of T and B lymphocytes by antigen presentation. Similar to other myeloid DCs, LCs bridge innate and adaptive immunity. Skin DCs differ in their C-type lectin receptor expression according to their site: langerin is expressed by epidermal LCs whereas DC-SIGN and mannose receptor are expressed by dermal DCs. In their resting state in the epidermis, the immature LCs are highly endocytic and efficient at antigen processing, but after inflammation, trauma or pathogen binding to TLRs, they mature and migrate to the draining lymph nodes while endocytic and antigen processing functions are downregulated. Here they present antigens to T cells, resulting in their activation.2,3 However, recent studies show that in some settings LCs may have an immunosuppressive role in the steady state4–7 and even lead to a regulatory T-cell response or deletional T-cell tolerance.

1Centre

Although LCs are the only DCs in the epidermis, a number of DC subsets have been described in the dermis of murine skin, which are distinguished by surface markers, morphology and in some cases, origin. Langerin was previously thought to be a specific marker for LC, but a number of groups have recently described langerin+dermal DC, which are distinguished from dermal DC by the expression of langerin, and from LC by the expression of CD103+ but not CD11b. They seem to be of different origin to LC,8–10 but their function has not been fully defined. In human skin no equivalent to the latter has yet been discovered. Dermal DCs may complement the roles of LCs by adopting the immunostimulatory activity previously attributed to LCs.11 LCs are of key importance in epitheliotropic virus infections as they are situated at the site of entry for viruses such as human immunodeficiency virus (HIV), the herpesviruses, including herpes simplex virus (HSV) and varicella-zoster virus (VZV), vaccinia and human papillomavirus. However, interactions of these viruses with LCs may have opposite outcomes for the virus–host balance. The host may derive advantage from viral capture and degradation and the induction of innate and adaptive immune responses or the virus may be favoured through infection and DC lysis or through protected transport and transfer to secondary cellular targets.12 In this review we will illustrate the contrasting interactions of LCs with HIV and with the herpesviruses. The herpesviruses, HSV and VZV, are classic epitheliotropic viruses that are able to infect both keratinocytes and LCs, although HSV is restricted to the epidermis whereas VZV also infects the dermis.13,14 However, HIV does not infect keratinocytes but must

for Virus Research, Westmead Millennium Institute, Westmead, New South Wales, Australia; 2Sydney Medical School, University of Sydney, Sydney, Australia; of Infectious Diseases, University of Sydney, Sydney, Australia and 4Kids Research Institute, Westmead, New South Wales, Australia Correspondence: Professor A Cunningham, Westmead Millennium Institute, Darcy Road, Westmead, New South Wales, 2145, Australia. E-mail: [email protected] Received 25 February 2010; accepted 25 February 2010 3Department

Viruses and Langerhans cells AL Cunningham et al 417

penetrate the superficial layers of the epidermis to gain access to potential resident targets cells, such as LCs and resting T lymphocytes. The nature of the interactions of the herpesviruses and HIV with LCs also differs markedly, with the former causing cytopathic or noncytopathic infection and the induction of robust innate and adaptive immune responses and the latter being noncytopathic and probably requiring LCs for protected transport to T cells. HIV and HSV have key pathogenetic interrelationships in that previous genital HSV2 infection enhances the risk of HIV acquisition three- to fourfold.15 HERPESVIRUSES AND LCS HSV interactions with DCs in epithelium HSV enters the body through breaks in the skin or mucosa, in which it first encounters immune cells within the skin. HSV establishes lifelong latent infection in the sensory ganglia after resolution of acute skin/ mucosal infection. Immune control of herpes occurs in both the skin and the dorsal root ganglion.16 After initial or recurrent HSV infection, the resident cells of the stratified squamous epidermis, keratinocytes and LCs are the initial responders to HSV infection, followed by infiltrating cells, such as monocytes/macrophages, natural killer cells, plasmacytoid DCs and CD4 lymphocytes, and then later predominantly CD8 lymphocytes. In murine models, innate mechanisms of immunity, interferons (IFNs), macrophages and natural killer cells form the first line of defence against initial HSV infection and disease, whereas neutralizing antibody and specific T lymphocytes, secreting antiviral cytokines and/or activated to kill infected cells, are required to clear productive HSV infection.16,17 In dorsal root ganglia, macrophages, T cells, especially non-cytotoxic CD8+ lymphocytes and also CD4 lymphcoytes, are important in the control of initial disease, maintenance of latency and prevention of spread into the central nervous system.16,18 Thus, HSV-specific CD4 and CD8 lymphocytes have a key role in controlling primary and recurrent HSV infections in humans and murine models and in recovery from infection. However, in mice, CD8 lymphocytes have a more prominent, earlier role in viral control and eradication as HSV immediate-early protein ICP47induced downregulation of major histocompatibility complex (MHC) class I on infected target cell is not as efficient.13,17,19–22 HSV infection of human keratinocytes in vitro induces the secretion of chemokines and cytokines in a defined sequence, which is similar to that in the vesicular lesion in vivo, that is, IFN-a and b-chemokines followed by interleukin (IL)-12 and then IL-1 and IL-6.23 The bchemokines initially attract monocytes and then, at a later stage, CD4 and CD8 lymphocytes into lesions. IFN-a and IL-12 induce a Th1 cytokine response from HSV antigen-stimulated CD4 (and CD8) lymphocytes. After HSV transmission from axon termini, IFN-a and IFN-g synergize to prevent or reduce infection of keratinocytes.24 HSV-1 or HSV-2 downregulate MHC class I expression by epidermal keratinocytes through the viral protein ICP47 interaction with cellular translocator-associated proteins in the endoplasmic reticulum.25,26 This is reversed by IFN-g mainly secreted by the CD4 lymphocytes infiltrating the lesion at early stages. The CD8 lymphocytes can recognize the infected keratinocytes after MHC I is restored on their surface by this IFN-g.11,13,17,20,27,28 IFN-g also stimulates MHC class II expression on keratinocytes in the lesion, allowing recognition by CD4+ lymphocytes. The later CD8 lymphocyte infiltrate seems to correlate with virus eradication from the skin. HSV infection of monocyte-derived DCs (MDDCs) in humans and bone marrow-derived DCs in mice has been described by our group and others. Although epidermal LCs are the obvious primary DCs to interact with HSV given their unique position in the epidermis in both humans and mice, the nature and consequence of this interaction

remains unclear. Recently, we have shown HSV structural antigens within epidermal LCs in initial murine recurrent HSV.29 One of the earliest studies on the role of LCs in anti-HSV responses showed that depletion of LCs from murine skin before footpad HSV-1 infection led to increased HSV virulence.30 Subsequently, LCs were reported to accumulate in the draining lymph nodes after subcutaneous administration of HSV-1, their numbers peaking at 3 days after infection. T lymphocytes from the lymph nodes of HSV-immunized mice responded to HSV antigen in vitro, but these responses declined after previous depletion of LCs from skin.31 Thus, these early studies suggested that LCs have a role in the induction of cellular immunity to HSV.32 One caveat of these early studies was that definitions of LCs may not have excluded other DC subsets in the skin, including dermal DC and the recently described langerin+dermal DC.9,11 However, in 2003, Allan et al.33 showed that in murine lymph nodes draining HSV lesions it was CD8 plus DCs and not LCs that presented HSV antigen to T cells. This paradox of initial HSV antigen uptake by LCs but presentation to T cells by another DC subtype could be explained by transfer of HSV antigens from one DC subtype to another.33 In view of the difficulty in obtaining sufficient numbers of immature human LCs, MDDCs have been used as a model. There is a dual interaction of HSV with MDDCs in humans34 and bone marrowderived DCs in mice:40 infection and antigen presentation. Both immature and mature MDDCs can be infected with HSV-1 and HSV-2 as they express the HSV receptors nectin-1, nectin-2 and herpesvirus entry mediator (HVEM). However, the infection is only productive in immature MDDCs, as mature DCs are only abortively infected.34–36 HSV infection of these DCs downregulates the key costimulatory molecules CD40, CD80, CD83 and CD86, and the adhesion molecule, CD54, thus preventing their maturation, even after exposure to the maturation stimuli, lipopolysaccharide, tumour necrosis factor-a or CD40L. Conversely, ultraviolet-inactivated HSV induces maturation.35,37,38 Unlike most other infected cells MHC class I is not downregulated by HSV,37 probably because the innately high levels of translocator-associated proteins in DCs overwhelm binding to the HSV ICP47. The earliest and most profound inhibition was observed with CD40 (and also CD54), which is important for the secretion of IL-12 by DCs.39,40 Furthermore HSV-1-infected DCs fail to produce IL-12 in response to lipopolysaccharide and CD40L.35,38 Preliminary experiments with immature LCs in vitro show a similar downregulation of costimulatory molecules (see below). As HSV induces such impairment of DC function, presumably infection is controlled by responses generated from uninfected DCs presenting cell debris and by cross-presentation of apoptotic HSV-infected DCs.33,34,41 Indeed, both HSV-1 and HSV-2 infections rapidly induce apoptosis of MDDCs (over 24 h) similar to their effects on monocytes and T cells, but in contrast to most other cell types in which HSV-1 is antiapoptotic.34,35,42,43 HSV-2 induces apoptosis more rapidly than HSV-1 in both human and murine bone marrow-derived DCs. These proapoptotic effects in haemopoietic cells are somewhat surprising as both HSV-1 and HSV-2 encode several gene products that effectively interfere with this pathway.44–50 These apoptotic cells can then be phagocytosed by uninfected bystander DCs, and the HSV antigens contained within them is cross-presented on MHC class I to CD8+ T cells.34 Other viral antigens have also been shown to be crosspresented in vitro similarly, including vaccinia virus, canarypox virus, HIV and human cytomegalovirus, among others.44,51–56 This type of cross-presentation may be the mechanism for the HSV antigen transfer between DC subtypes observed in murine models. Thus, the virus-induced immunoevasive mechanisms of impaired DC Immunology and Cell Biology


Figure 1 Postulated interactions between HSV and DCs in the epidermis and transport of antigen to lymph node. HSV infection of epidermis LCs induces apoptosis, followed by uptake by bystander LCs or dermal DCs moving into the area of inflammation. Cytokines/danger signals released from infected keratinocytes lead to maturation and migration of DCs to lymph nodes in which they activate CD4+ or CD8+ lymphocytes directly or through intermediate DCs (Modified with permission from Viral Immunol Ref. 115 r (2005) Mary Ann Liebert, Inc.).

maturation and subsequent apoptosis by HSV can be counteracted by HSV antigen uptake by bystander DCs (Figure 1). Murine models of HSV-infected skin have recently provided supportive evidence for these hypotheses. Using a model of in vitrocultured full-thickness ear skin to study the effects of HSV on LC emigration from the skin, we have observed HSV structural antigens within epidermal LCs in murine skin explants after primary infection (Putter FK et al., unpublished data).We have also observed that human LCs can be directly infected with HSV in studies with skin from biopsies of recurrent herpes simplex vesicles (L Bosnjak et al., unpublished data). It has also been observed that HIV-infected murine cutaneous LCs undergo apoptosis similar to HSV-infected MDDCs and bone marrow-derived DCs. Already however, the mechanism, timing and site of HSV antigen transfer to other DC subsets remain to be elucidated. In vivo models of HSV using a flank murine model of infection, in which keratin is removed by a drill to induce uniform high levels of infection, suggest that migratory and resident DC subsets have distinct roles in the induction of protective immunity to HSV.12,33,57 At early stages in murine lymph node, resident CD8 and DCs are the only DC subsets presenting HSV antigen to T cells. The zosteriform model examines cutaneous infection after a neural loop to the dorsal root ganglion, and is more akin to recurrent than initial infection as viruses re-enter the skin from nerve terminals, although there is no true latency or reactivation. Recent work using this model suggests that although LCs are capable of activating naive T cells, they are not the major subset to do so and that langerin expressing CD103+DC are the main migratory subset to present HSV antigens to CD8+ T cells in lymph nodes,33,56,58 and they might also be the dermal DCs presenting HSV antigen to CD4+ T cells after murine vaginal HSV infection.11 These murine and human data suggest a complex in vivo scenario in acute HSV infection. Initial infection of epidermal cells will result in infection of resident LCs as they come into direct contact with the incoming virus. Such infected LCs may resist further maturation Immunology and Cell Biology

stimuli provided by tumour necrosis factor-a and IL-1b from infected keratinocytes and may undergo apoptosis at the site of infection or the dermis as they migrate towards the lymphatics. Thus, apoptotic LC fragments may be phagocytosed by bystander uninfected LCs or by (langerin+) dermal DCs for cross-presentation. Murine studies suggest that at least some of this transfer also occurs within the draining lymph node as the CD8+ DC population responsible for the activation of HSV-specific CD8+ T cells resides in lymph nodes.33,57 In addition, it remains possible that virus or viral antigen may ‘leak’ into the lymphoid compartment, allowing uptake by (or even infection) of lymph node-resident DCs—although attenuation of T cell priming by inhibiting skin DC migration argues that this may not be a dominant mechanism of lymph node access.33 Although not disputing the above hypothesis, other studies indicate that the antigen transfer may also occur adjacent to the site of infection and subsequently activate CD4+ T lymphocytes in the lymph node.11 Therefore, there may be different locations of antigen uptake/transfer to DCs for stimulation of CD4+ or CD8+ T lymphocytes. The precise sequence of events of HSV antigen transfer from keratinocytes and LCs to other cutaneous DC subsets and the site of demise of infected LCs still need to be elucidated. The role of LCs in varicella-zoster disease VZV causes varicella (chickenpox) and herpes zoster (shingles). During primary infection causing varicella characterized by a generalized vesiculopustular rash, VZV establishes latent infection of the sensory ganglia, from which virus may reactivate years later to cause herpes zoster. The characteristic vesiculopustular rash of herpes zoster only differs from that of varicella in that the distribution of the lesions is typically unilateral and covers only 1to 2 dermatomes.58,59 DCs of the respiratory mucosa may be among the first cells to encounter VZV during primary infection and are capable of viral transport to human tonsillar CD4+ T lymphocytes. These T lymphocytes express skin homing markers that may allow them to transport VZV directly from


the lymph node to the skin during the primary viraemia.60,61 Once the virus reaches the skin, it infects cutaneous epithelial cells resulting in distinctive vesiculopustular lesions.58,62,63 There is extensive cytopathic effect on keratinocytes resulting in vesicles containing abundant IFNs and other cytokines, similar to herpes simplex lesions. In both the rashes of varicella and herpes zoster, VZV antigens are detectable in the epidermis and dermis.63–67 The type and distribution of changes in DC subsets that occur in the skin of humans suffering from varicella or herpes zoster has recently been studied and compared with herpes simplex lesions. The proportions of DC-SIGN+dermal DCs were not significantly altered in HSV, VZV or HZ lesional skin. However, unlike HSV, epidermal LCs are strikingly depleted.67,68 The presence of structural and nonstructural VZV proteins in these cells was consistent with replicating virus, suggesting that some of these DCs become infected in vivo. Similar to HSV, plasmacytoid DCs, the potent secretors of type I IFN, infiltrate the lesions. Some of the LCs and plasmacytoid DCs were VZV antigen positive and both were closely associated with VZV antigen-positive keratinocytes or fibroblasts, respectively. In vitro plasmacytoid DCs isolated from human blood and model LCs derived from MUTZ-3 cells as well as MDDCs were permissive to VZV infection. In VZV infected plasmacytoid DC IFN-a was not induced, indicating that viral infection inhibits its secretion. In addition, infected plasmacytoid DC remained refactory to IFN-a induction even when stimulated with a TLR9 agonist that stimulates IFN-a production by plasmacytoid DC. Further work will be required to define the inhibitous mechanism and identify viral gene(s) that encode this function. The marked depletion of epidermal LCs during VZV infection was not due to loss of expression of the surface markers, CD1a and langerin, on LCs that remain in the skin, as langerin staining remained abundant on both infected and uninfected LCs.69 VZV-infected MUTZ3-derived LCs also did not lose langerin expression. Furthermore, there was no significant level of apoptosis in VZV-infected MUTZ3-derived LCs by TUNEL (TdT-mediated dUTP nick end labeling) staining.69 Thus, the depletion is probably due to LC emigration to lymph nodes, in which additional T lymphocyte priming may occur. In view of the marked depletion, bystander LCs with or without VZV antigen must also emigrate. Infected LCs could also be having a role in virus spread. Thus, LCs in both the skin and the respiratory mucosa may be involved in the early stages of VZV pathogenesis.61 LCs present in the respiratory mucosa may be the first cells to become infected with VZV and travel to the lymph nodes in which they then infect T lymphocytes. VZV-infected T lymphocytes then migrate to the skin as part of the inflammatory infiltrate,67–69 in which they are among the cells responsible for spreading VZV to cutaneous cells. The development of lesions in the typical course of varicella occurs in crops over several days,58 and hence after initial infiltration of VZV-infected immune cells, infected cutaneous LCs emigrating to draining lymph nodes may infect additional T lymphocytes that then migrate back to the skin to cause additional skin lesions. A more recent study has shown CD14+ monocytes within varicella lesions that express T lymphocyte costimulatory molecules. It was shown in vitro that monocytes can be induced by IFN-a to express T-lymphocyte costimulatory molecules and can then present VZV antigen to T lymphocytes.70 However, the infiltrating plasmacytoid DCs do not express the key maturation marker, CD83, suggesting that plasmacytoid DCs may not mature in VZV-infected skin in vivo. In recurrent genital herpes lesions, plasmacytoid DCs also infiltrate the dermis and at the dermo–epidermal junction in close proximity to

T lymphocytes, particularly CD69+ activated T lymphocytes.71 In contrast to VZV blood plasmacytoid DCs do not become infected with HSV-2, but plasmacytoid DCs exposed to HSV-2 were able to mature and also stimulate virus-specific autologous T-lymphocyte proliferation.68,71,72 Furthermore, VZV-infected plasmacytoid DCs did not secrete significant amounts of IFN-a, yet plasmacytoid DCs exposed to HSV-1 or HSV-2 produced large amounts of IFN-a.73,74 Thus, there are fundamental differences between human a-herpesviruses in their interactions with LCs and other DCs in the skin. VZV and HSV have clearly evolved different strategies to cause disease in the human host. Further definition of the precise role of LCs and other interacting DCs in epithelial viral infections in vivo is critical to the development of topical microbicides and mucosal vaccines against HSV, VZV and vaccinia. INTERACTIONS OF HIV WITH LCS The majority of global HIV transmission is through male-to-female or female-to-male sexual intercourse with or without accompanying sexually transmitted infections. Genital ulcerative diseases such as genital herpes may enhance HIV acquisition three- to fourfold not only by facilitating infection through epithelial breaches, but also through provision of the appropriate target cells in the inflammatory infiltrate.75 The mechanisms of HIV entry into the normal uninflamed female genital tract is slowly being clarified but certain aspects remain controversial, including the importance of ‘microabrasions’ and the relative importance of resident LCs, CD4T lymphocytes and perhaps even macrophages.76–78 A practical aspect of their relative roles relates to development of second-generation vaginal microbicides to prevent heterosexual HIV-1 transmission. If successful, this would contain the spread of the virus, especially in developing countries where condom use and roll-out of prophylactic antiretrovirals has proven inadequate. The first and second generation of physicochemical microbicides have failed in recent clinical trials.79–81 Although the first generation of detergent-based microbicides (for example, nonoxynol-9) enhanced HIV infection because of inflammation of the anogenital mucosa, the reasons for failure of the second-generation polyanion-based microbicides seem to be more complex. The lessons learnt from the two trials is the need for more research on the mechanism of HIV-1 transmission and development of specific inhibitors.82 Furthermore, the role of LCs and other epithelial DCs is relevant to development of mucosal HIV vaccines.83 As LCs are the major resident cell type in the cervicovaginal and penile stratified squamous epithelium that are able to be infected by HIV or simian immunodeficiency virus in macaque models, their role in initial HIV/simian immunodeficiency virus acquisition has long been suspected and is now supported by in vivo and ex vivo data, with some still unpublished.84,85 Vaginal simian immunodeficiency virus infection of Rhesus macaques resulted in infected LCs within the first day of infection and studies with biopsies of human cervical and skin of primate foreskin tissue explants show that LCs can be infected.85 LCs and resting T lymphocytes were also the major cell types expressing HIV antigen after topical infection of human vaginal epithelial explants. After emigration from the explants often as doublets, both cell types expressed HIV antigen, which was often concentrated at their contact region,84 suggesting transfer of HIV from LCs to CD4 lymphocytes (see below). These LCs may also provide protected intracellular transport of HIV to CD4 lymphocytes, firstly in the submucosal lymphoid tissue and then to draining lymph nodes.12,78,84,85 Immunology and Cell Biology


Comparison of HIV interactions with monocyte-derived DCs and LCs Studies on HIV infection of primary LCs are difficult because they comprise only 1–2% of cells in stratified squamous epithelium, and keratinocytes are strongly adherent to them and each other, thus resisting dissociation. In vitro models that closely resemble LCs have been difficult to develop and are still being refined. Nevertheless, LCs can be isolated from human skin in vitro by two main methods: emigration from split skin explants or enzymatic (trypsin/collagenase) digestion and flow sorting or magnetic-activated cell sorting bead technology. The latter offers better preservation of the immature phenotype but is labour intensive, technically difficult and care must be taken that the enzymatic treatment does not remove cellsurface proteins such as CD4 or alter the final LC phenotype.86 Therefore, many preliminary studies have been conducted in human model MDDCs in vitro. However, such DCs more closely resemble dermal or lamina propria DCs, particularly in the types of C-type lectin receptors expressed. MDDCs capture HIV predominantly through the C-type lectin receptor DC-SIGN87,88 and also, mannose receptor and to a lesser degree through heparin sulphate proteoglycan syndecan3.86,88,89 HIV-1 is then either endocytosed or transferred directly to CD4 and CCR5, resulting in viral-cell membrane fusion and infection.87,88 Immature DCs and LCs express high levels of CCR5 but on maturation CCR5 is downregulated and CXCR4 upregulated, resulting in reduced infectability by R5 (CCR5 using) viral strains, the strains shown to be predominant during sexual transmission.90 In immature LCs and DCs, HIV binding to langerin or DC-SIGN leads to viral endocytosis and then almost complete degradation.88,91,92 However, there is residual long-term viral survival in MDDCs and how this occurs is the subject of much conjecture. For instance, is this small proportion of virus internalized through a different intracellular route or alternatively have they ‘escaped’ from degradation through an unknown mechanism to enter a ‘protected vesicle’? Further studies on the latter vesicle have now shown that it is not a closed structure, but an invagination of the plasma membrane rich in tetraspanins such as CD81.93 One apparent difference between immature DCs and LCs in HIV trafficking seems to be the relative effects of DC-SIGN and langerin binding on HIV replication, although this is still very controversial (see van der Vlist and Geijtenbeck,94 this issue). Although it is clear that DC-SIGN binding of HIV enhances viral-cell membrane fusion and infection of immature DCs,87,88,93 little data are available to suggest the same for langerin. In contrast, one research group reports no role of langerin in LC infection,95 whereas another reports that blocking enhances LC infection, which is the opposite of DC-SIGN.91 However, viral infusion and HIV infection in LCs/DCs after CD4/ CCR5 binding leads to de novo productive infection, first detectable at 24–48 h with a plateau at 96–120 h in vitro.92 Recent studies suggest that this de novo-produced virus can re-enter the same or adjacent DCs by endocytosis and this creates two distinct viral pools within the same cell. Contact between DCs that have captured HIV with activated or non-activated CD4 lymphocytes leads to efficient transfer of virus to lymphocytes.92,96–98 The mechanism of this transfer depends on the particular pool of virus in any one DC. For instance, DCs that contact T cells o24 h after HIV exposure would have only a vesicular pool of virus and thus transfer virus through a ‘first phase viral synapse (VS)’ at the contact region between the two cell types. After DCs are infected they contain two pools of virus, one from newly forming virions originating from the cytosol and the second from previously budding virions that have now recirculated back into the DCs as a vesicular Immunology and Cell Biology

Figure 2 Schematic summary of viral transfer from infected DCs to CD4 T cells over time. Phases of DC viral transfer are indicated over time. Each phase is labeled at the top of each panel, with schematic DC–T-cell viral transfer drawn above. Note that phase III is a mechanistic combination of phases I and II.

reservoir. Thus, with two distinct pools of virus, there must be two further forms of VS for viral transfer, a ‘second phase VS’ for de novo forming virus and, for virus taken up again within vesicles, a ‘third phase VS’. This is summarized in Figure 2. In LCs the relative importance of these two stages is still debated. Several studies have shown that LC infection with R5-tropic HIV-1 is essential to its role in transmission.90,95 However, recently it was shown that mature CD34+-derived LC-like cells can transmit HIV-1 without infection, and in vaginal LCs HIV can be transferred in a first phase VS in a very similar manner to MDDCs.84,99 Another difference in LCs from MDDCs with respect to HIV infection occurs after the process of maturation. In MDDCs, maturation leads to two quite distinct differences in viral handling. As opposed to immature DCs, mature DCs have sequester a greater number of virions within vesicular compartments for longer periods of time.100,101 Indeed, mature MDDCs are more potent than immature MDDCs in first phase transfer.102,103 but how they conserve a greater proportion of virions is unknown. One hypothesis is that as several members of the tetraspanin family (including CD81, CD82 and CD9) are observed within the vesicle that sequesters the virus, they may be involved in positively regulating virion survival by preventing endolysosomal fusion.94,104,105 Another difference in mature versus immature DCs is the lower rate of de novo (productive) infection,106 possibly because of lower viral-cell fusion, increased levels of the anti-HIV restriction factor active Apobec3107 and additional transcription blocks, resulting in less transfer to T cells through second phase VS.92 LCs do not seem to follow this paradigm, but rather seem to be more susceptible to HIV when exposed to various maturation stimuli. For instance, tumour necrosis factor-a and TLR-3 agonists can increase LC infection,108 whereas Gram-positive bacteria also stimulate HIV replication through TLR1/2 and TLR2/6.109 Given the recent observations of maturing LCs becoming more permissive to HIV infection, this may explain, to some extent, the reported discrepancies in the effects of langerin inhibition. For instance, the process of epidermal cell dissociation, followed by LC isolation in vitro may render them more permissive (as this would be a form of ‘tissue trauma’ and thus a primary stimulus to commence LC maturation) to HIV infection after langerin binding.


The effect of HIV on LC function, especially on the anti-HIV immune response, is yet to be shown. HIV containing DCs can present antigen to HIV-specific CD4 lymphocytes as well as transfer HIV to them, thus resulting in their death. Thus, there is now evidence for selective depletion of HIV-specific CD4 lymphocytes through this mechanism.110,111 HIV infection markedly affects the function of CD4 lymphocytes even before inducing lysis or apoptosis. Similarly, HIV infection of DCs also affects their function in multiple but more subtle ways. In MDDCs there are two phases of altered gene expression corresponding to endocytosis and de novo infection that are therefore likely to affect two phases of transfer in different ways. Recent studies show that when a substantial proportion of DCs or LCs are infected they undergo partial maturation and enhanced migration.96,112–114 The partial maturation is sufficient to enhance T-cell stimulation and might also enhance DC–T-cell adhesion, reduce endosomal degradation and maintain productive DC infection, thus culminating in increased viral transfer and, in vivo, enhance overall viral spread and impair antiviral immunity. However, infection of MDDCs also inhibits lysosomal enzyme expression and function, especially those cathepsins involved in acid-proteolytic endosomal digestion of virus and also in the processing of viral and other antigens. These changes are likely to enhance virus survival in endosomes and increase the infectious vesicular pool of virus that is transferred at a later time to CD4 T cells (see phase III of viral transfer in Figure 2) and also to inhibit antigen presentation, perhaps contributing to HIV-induced immunosuppression. Whether HIV also induces such changes in LCs is yet to be determined, but is a subject of continuing investigation.

2

3 4 5

6

7 8

9 10

11

12 13 14

15 16

CONCLUSIONS Thus, although HIV, VZV and HSV interact with LCs during initial infection of the female genital tract, the effects are quite different, reflecting differences in biology and pathogenesis. After LCs capture HIV this is followed by degradation or de novo infection and under specific conditions, HIV probably uses LCs for transfer to CD4 lymphocytes in the submucosa and subsequent dissemination. Whether langerin has a key role in (inhibiting) infection requires resolution. HSV infects LCs, which probably facilitates transfer to another type of DC in lymph node responsible for subsequent antigen presentation to CD8 T cells. Whether dermal LCs or another similar subset have any role in HSV (antigen) transport to lymph nodes requires further work. VZV is the most complex as it induces marked emigration of (uninfected and infected) LCs from the epidermis, induces plasmacytoid DC immigration into lesions and is able to infect LCs, plasmacytoid DCs and probably dermal DCs. The exact role of these DC subsets in transfer of virus to T cells, VZV antigen presentation to T cells and impairment of their function by infection requires much future work.

17

CONFLICT OF INTEREST The authors declare no conflict of interest.

27

18 19 20

21

22

23

24

25

26

28

ACKNOWLEDGEMENTS We acknowledge the intellectual input from Andrew Harman and Heather Donaghy. ALC, CJ, AA and ST are supported by program and project grants from the National Health and Medical Research Council of Australia. We thank Ivy Shih for the amendment and adaptation of Figure 1.

29

30 31

1

Romani N, Clausen BE, Stoitzner P. Langerhans cells and more: langerin-expressing dendritic cell subsets in the skin. Immunol Rev 2010; 234: 120–141.

32

Mayerova D, Parke EA, Bursch LS, Odumade OA, Hogquist KA. Langerhans cells activate naive self-antigen-specific CD8 T cells in the steady state. Immunity 2004; 21: 391–400. Zaba LC, Krueger JG, Lowes MA. Resident and ‘inflammatory’ dendritic cells in human skin. J Invest Dermatol 2009; 129: 302–308. Cumberbatch M, Singh M, Dearman RJ, Young HS, Kimber I, Griffiths CE. Impaired Langerhans cell migration in psoriasis. J Exp Med 2006; 203: 953–960. Jiang A, Bloom O, Ono S, Cui W, Unternaehrer J, Jiang S et al. Disruption of Ecadherin-mediated adhesion induces a functionally distinct pathway of dendritic cell maturation. Immunity 2007; 27: 610–624. Kaplan DH, Jenison MC, Saeland S, Shlomchik WD, Shlomchik MJ. Epidermal Langerhans cell-deficient mice develop enhanced contact hypersensitivity. Immunity 2005; 23: 611–620. Loser K, Beissert S. Dendritic cells and T cells in the regulation of cutaneous immunity. Adv Dermatol 2007; 23: 307–333. Bursch LS, Wang L, Igyarto B, Kissenpfennig A, Malissen B, Kaplan DH et al. Identification of a novel population of Langerin+ dendritic cells. J Exp Med 2007; 204: 3147–3156. Merad M, Ginhoux F, Collin M. Origin, homeostasis and function of Langerhans cells and other langerin-expressing dendritic cells. Nat Rev Immunol 2008; 8: 935–947. Poulin LF, Henri S, de Bovis B, Devilard E, Kissenpfennig A, Malissen B. The dermis contains langerin+ dendritic cells that develop and function independently of epidermal Langerhans cells. J Exp Med 2007; 204: 3119–3131. Zhao X, Deak E, Soderberg K, Linehan M, Spezzano D, Zhu J et al. Vaginal submucosal dendritic cells, but not Langerhans cells, induce protective Th1 responses to herpes simplex virus-2. J Exp Med 2003; 197: 153–162. Cunningham AL, Carbone F, Geijtenbeek TB. Langerhans cells and viral immunity. Eur J Immunol 2008; 38: 2377–2385. Cunningham AL, Turner RR, Miller AC, Para MF, Merigan TC. Evolution of recurrent herpes simplex lesions. An immunohistologic study. J Clin Invest 1985; 75: 226–233. Nikkels AF, Debrus S, Sadzot-Delvaux C, Piette J, Delvenne P, Rentier B et al. Comparative immunohistochemical study of herpes simplex and varicella-zoster infections. Virchows Arch A Pathol Anat Histopathol 1993; 422: 121–126. Wald A, Link K. Risk of human immunodeficiency virus infection in herpes simplex virus type 2-seropositive persons: a meta-analysis. J Infect Dis 2002; 185: 45–52. Cunningham AL, Diefenbach RJ, Miranda-Saksena M, Bosnjak L, Kim M, Jones C et al. The cycle of human herpes simplex virus infection: virus transport and immune control. J Infect Dis 2006; 194 (Suppl 1): S11–S18. Koelle DM, Corey L. Herpes simplex: insights on pathogenesis and possible vaccines. Annu Rev Med 2008; 59: 381–395. Divito S, Cherpes TL, Hendricks RL. A triple entente: virus, neurons, and CD8+ T cells maintain HSV-1 latency. Immunol Res 2006; 36: 119–126. Khanna KM, Lepisto AJ, Decman V, Hendricks RL. Immune control of herpes simplex virus during latency. Curr Opin Immunol 2004; 16: 463–469. Koelle DM, Frank JM, Johnson ML, Kwok WW. Recognition of herpes simplex virus type 2 tegument proteins by CD4 T cells infiltrating human genital herpes lesions. J Virol 1998; 72: 7476–7483. Simmons A, Tscharke DC. Anti-CD8 impairs clearance of herpes simplex virus from the nervous system: implications for the fate of virally infected neurons. J Exp Med 1992; 175: 1337–1344. Verjans GM, Hintzen RQ, van Dun JM, Poot A, Milikan JC, Laman JD et al. Selective retention of herpes simplex virus-specific T cells in latently infected human trigeminal ganglia. Proc Natl Acad Sci USA 2007; 104: 3496–3501. Mikloska Z, Danis VA, Adams S, Lloyd AR, Adrian DL, Cunningham AL. In vivo production of cytokines and beta (C-C) chemokines in human recurrent herpes simplex lesions—do herpes simplex virus-infected keratinocytes contribute to their production? J Infect Dis 1998; 177: 827–838. Mikloska Z, Cunningham AL. Alpha and gamma interferons inhibit herpes simplex virus type 1 infection and spread in epidermal cells after axonal transmission. J Virol 2001; 75: 11821–11826. York IA, Roop C, Andrews DW, Riddell SR, Graham FL, Johnson DC. A cytosolic herpes simplex virus protein inhibits antigen presentation to CD8+ T lymphocytes. Cell 1994; 77: 525–535. York IA, Johnson DC. Direct contact with herpes simplex virus-infected cells results in inhibition of lymphokine-activated killer cells because of cell-to-cell spread of virus. J Infect Dis 1993; 168: 1127–1132. Mikloska Z, Kesson AM, Penfold ME, Cunningham AL. Herpes simplex virus protein targets for CD4 and CD8 lymphocyte cytotoxicity in cultured epidermal keratinocytes treated with interferon-gamma. J Infect Dis 1996; 173: 7–17. Koelle DM, Posavad CM, Barnum GR, Johnson ML, Frank JM, Corey L. Clearance of HSV-2 from recurrent genital lesions correlates with infiltration of HSV-specific cytotoxic T lymphocytes. J Clin Invest 1998; 101: 1500–1508. Putter FK, Fernandez MA, Cunningham AL, Jones CA. Epidermal Langerhans cells (LC) are targets for herpes simplex virus (HSV) infection in vitro and in vivo, and undergo apoptosis upon infection. Proceedings of the 10th International Symposium on Dendritic Cells, Kobe, Japan, Kobe, Japan. Abstract no. P6–16: 23 2008. Sprecher E, Becker Y. Skin Langerhans cells play an essential role in the defense against HSV-1 infection. Arch Virol 1986; 91: 341–349. Sprecher E, Becker Y. Langerhans cell density and activity in mouse skin and lymph nodes affect herpes simplex type 1 (HSV-1) pathogenicity. Arch Virol 1989; 107: 191–205. Sprecher E, Becker Y. Detection of IL-1 beta, TNF-alpha, and IL-6 gene transcription by the polymerase chain reaction in keratinocytes, Langerhans cells and peritoneal

Immunology and Cell Biology


33

34

35

36

37

38 39

40 41

42

43

44

45 46

47

48

49

50

51

52

53

54

55

56

57

58 59

exudate cells during infection with herpes simplex virus-1. Arch Virol 1992; 126: 253–269. Allan RS, Smith CM, Belz GT, van Lint AL, Wakim LM, Heath WR et al. Epidermal viral immunity induced by CD8alpha+ dendritic cells but not by Langerhans cells. Science 2003; 301: 1925–1928. Bosnjak L, Miranda-Saksena M, Koelle DM, Boadle RA, Jones CA, Cunningham AL. Herpes simplex virus infection of human dendritic cells induces apoptosis and allows cross-presentation via uninfected dendritic cells. J Immunol 2005; 174: 2220–2227. Jones CA, Fernandez M, Herc K, Bosnjak L, Miranda-Saksena M, Boadle RA et al. Herpes simplex virus type 2 induces rapid cell death and functional impairment of murine dendritic cells in vitro. J Virol 2003; 77: 11139–11149. Kruse M, Rosorius O, Kratzer F, Stelz G, Kuhnt C, Schuler G et al. Mature dendritic cells infected with herpes simplex virus type 1 exhibit inhibited T-cell stimulatory capacity. J Virol 2000; 74: 7127–7136. Mikloska Z, Bosnjak L, Cunningham AL. Immature monocyte-derived dendritic cells are productively infected with herpes simplex virus type 1. J Virol 2001; 75: 5958–5964. Salio M, Cella M, Suter M, Lanzavecchia A. Inhibition of dendritic cell maturation by herpes simplex virus. Eur J Immunol 1999; 29: 3245–3253. Cella M, Facchetti F, Lanzavecchia A, Colonna M. Plasmacytoid dendritic cells activated by influenza virus and CD40L drive a potent TH1 polarization. Nat Immunol 2000; 1: 305–310. Snijders A, Kalinski P, Hilkens CM, Kapsenberg ML. High-level IL-12 production by human dendritic cells requires two signals. Int Immunol 1998; 10: 1593–1598. Allan RS, Waithman J, Bedoui S, Jones CM, Villadangos JA, Zhan Y et al. Migratory dendritic cells transfer antigen to a lymph node-resident dendritic cell population for efficient CTL priming. Immunity 2006; 25: 153–162. Mastino A, Sciortino MT, Medici MA, Perri D, Ammendolia MG, Grelli S et al. Herpes simplex virus 2 causes apoptotic infection in monocytoid cells. Cell Death Differ 1997; 4: 629–638. Raftery MJ, Behrens CK, Muller A, Krammer PH, Walczak H, Schonrich G. Herpes simplex virus type 1 infection of activated cytotoxic T cells: induction of fratricide as a mechanism of viral immune evasion. J Exp Med 1999; 190: 1103–1114. Arrode G, Boccaccio C, Lule J, Allart S, Moinard N, Abastado JP et al. Incoming human cytomegalovirus pp65 (UL83) contained in apoptotic infected fibroblasts is cross-presented to CD8(+) T cells by dendritic cells. J Virol 2000; 74: 10018–10024. Aubert M, O’Toole J, Blaho JA. Induction and prevention of apoptosis in human HEp-2 cells by herpes simplex virus type 1. J Virol 1999; 73: 10359–10370. Aubert M, Rice SA, Blaho JA. Accumulation of herpes simplex virus type 1 early and leaky-late proteins correlates with apoptosis prevention in infected human HEp-2 cells. J Virol 2001; 75: 1013–1030. Galvan V, Roizman B. Herpes simplex virus 1 induces and blocks apoptosis at multiple steps during infection and protects cells from exogenous inducers in a cell-typedependent manner. Proc Natl Acad Sci USA 1998; 95: 3931–3936. Jerome KR, Fox R, Chen Z, Sears AE, Lee H, Corey L. Herpes simplex virus inhibits apoptosis through the action of two genes, Us5 and Us3. J Virol 1999; 73: 8950–8957. Perkins D, Pereira EF, Aurelian L. The herpes simplex virus type 2 R1 protein kinase (ICP10 PK) functions as a dominant regulator of apoptosis in hippocampal neurons involving activation of the ERK survival pathway and upregulation of the antiapoptotic protein Bag-1. J Virol 2003; 77: 1292–1305. Zhou G, Roizman B. The domains of glycoprotein D required to block apoptosis depend on whether glycoprotein D is present in the virions carrying herpes simplex virus 1 genome lacking the gene encoding the glycoprotein. J Virol 2001; 75: 6166–6172. Fonteneau JF, Gilliet M, Larsson M, Dasilva I, Munz C, Liu YJ et al. Activation of influenza virus-specific CD4+ and CD8+ T cells: a new role for plasmacytoid dendritic cells in adaptive immunity. Blood 2003; 101: 3520–3526. Larsson M, Fonteneau JF, Somersan S, Sanders C, Bickham K, Thomas EK et al. Efficiency of cross presentation of vaccinia virus-derived antigens by human dendritic cells. Eur J Immunol 2001; 31: 3432–3442. Motta I, Andre F, Lim A, Tartaglia J, Cox WI, Zitvogel L et al. Cross-presentation by dendritic cells of tumor antigen expressed in apoptotic recombinant canarypox virusinfected dendritic cells. J Immunol 2001; 167: 1795–1802. Larsson M, Fonteneau JF, Lirvall M, Haslett P, Lifson JD, Bhardwaj N. Activation of HIV-1 specific CD4 and CD8 T cells by human dendritic cells: roles for crosspresentation and non-infectious HIV-1 virus. AIDS 2002; 16: 1319–1329. Maranon C, Desoutter JF, Hoeffel G, Cohen W, Hanau D, Hosmalin A. Dendritic cells cross-present HIV antigens from live as well as apoptotic infected CD4+ T lymphocytes. Proc Natl Acad Sci USA 2004; 101: 6092–6097. Bedoui S, Whitney PG, Waithman J, Eidsmo L, Wakim L, Caminschi I et al. Crosspresentation of viral and self antigens by skin-derived CD103+ dendritic cells. Nat Immunol 2009; 10: 488–495. Belz GT, Smith CM, Eichner D, Shortman K, Karupiah G, Carbone FR et al. Cutting edge: conventional CD8 alpha+ dendritic cells are generally involved in priming CTL immunity to viruses. J Immunol 2004; 172: 1996–2000. Chen TM, George S, Woodruff CA, Hsu S. Clinical manifestations of varicella-zoster virus infection. Dermatol Clin 2002; 20: 267–282. Mahalingam R, Wellish M, Wolf W, Dueland AN, Cohrs R, Vafai A et al. Latent varicella-zoster viral DNA in human trigeminal and thoracic ganglia. N Engl J Med 1990; 323: 627–631.


60 Ku CC, Padilla JA, Grose C, Butcher EC, Arvin AM. Tropism of varicella-zoster virus for human tonsillar CD4(+) T lymphocytes that express activation, memory, and skin homing markers. J Virol 2002; 76: 11425–11433. 61 Ku CC, Zerboni L, Ito H, Graham BS, Wallace M, Arvin AM. Varicella-zoster virus transfer to skin by T Cells and modulation of viral replication by epidermal cell interferon-alpha. J Exp Med 2004; 200: 917–925. 62 Arvin AM, Moffat JF, Redman R. Varicella-zoster virus: aspects of pathogenesis and host response to natural infection and varicella vaccine. Adv Virus Res 1996; 46: 263–309. 63 Muraki R, Baba T, Iwasaki T, Sata T, Kurata T. Immunohistochemical study of skin lesions in herpes zoster. Virchows Arch A Pathol Anat Histopathol 1992; 420: 71–76. 64 Muraki R, Iwasaki T, Sata T, Sato Y, Kurata T. Hair follicle involvement in herpes zoster: pathway of viral spread from ganglia to skin. Virchows Arch 1996; 428: 275–280. 65 Nikkels AF, Debrus S, Sadzot-Delvaux C, Piette J, Rentier B, Pierard GE. Localization of varicella-zoster virus nucleic acids and proteins in human skin. Neurology 1995; 45: S47–S49. 66 Nikkels AF, Delvenne P, Debrus S, Sadzot-Delvaux C, Piette J, Rentier B et al. Distribution of varicella-zoster virus gpI and gpII and corresponding genome sequences in the skin. J Med Virol 1995; 46: 91–96. 67 Nikkels AF, Sadzot-Delvaux C, Pierard GE. Absence of intercellular adhesion molecule 1 expression in varicella zoster virus-infected keratinocytes during herpes zoster: another immune evasion strategy? Am J Dermatopathol 2004; 26: 27–32. 68 Leinweber B, Kerl H, Cerroni L. Histopathologic features of cutaneous herpes virus infections (herpes simplex, herpes varicella/zoster): a broad spectrum of presentations with common pseudolymphomatous aspects. Am J Surg Pathol 2006; 30: 50–58. 69 Huch JH, Cunningham AL, Arvin AM, Nasr N, Santegoets SJ, Slobedman E et al. Impact of varicella zoster virus on dendritic cell subsets in human skin during natural infection. J Virol 2010; 84: 4060–4072. 70 Gerlini G, Mariotti G, Chiarugi A, Di Gennaro P, Caporale R, Parenti A et al. Induction of CD83+CD14+ nondendritic antigen-presenting cells by exposure of monocytes to IFN-alpha. J Immunol 2008; 181: 2999–3008. 71 Donaghy H, Bosnjak L, Harman AN, Marsden V, Tyring SK, Meng TC et al. Role for plasmacytoid dendritic cells in the immune control of recurrent human herpes simplex virus infection. J Virol 2009; 83: 1952–1961. 72 Gerlini G, Mariotti G, Bianchi B, Pimpinelli N. Massive recruitment of type I interferon producing plasmacytoid dendritic cells in varicella skin lesions. J Invest Dermatol 2006; 126: 507–509. 73 Fitzgerald-Bocarsly P. Human natural interferon-alpha producing cells. Pharmacol Ther 1993; 60: 39–62. 74 Siegal FP, Kadowaki N, Shodell M, Fitzgerald-Bocarsly PA, Shah K, Ho S et al. The nature of the principal type 1 interferon-producing cells in human blood. Science 1999; 284: 1835–1837. 75 Zhu J, Hladik F, Woodward A, Klock A, Peng T, Johnston C et al. Persistence of HIV-1 receptor-positive cells after HSV-2 reactivation is a potential mechanism for increased HIV-1 acquisition. Nat Med 2009; 15: 886–892. 76 Gupta P, Collins KB, Ratner D, Watkins S, Naus GJ, Landers DV et al. Memory CD4(+) T cells are the earliest detectable human immunodeficiency virus type 1 (HIV-1)infected cells in the female genital mucosal tissue during HIV-1 transmission in an organ culture system. J Virol 2002; 76: 9868–9876. 77 Shattock RJ, Moore JP. Inhibiting sexual transmission of HIV-1 infection. Nat Rev Microbiol 2003; 1: 25–34. 78 Zhang Z, Schuler T, Zupancic M, Wietgrefe S, Staskus KA, Reimann KA et al. Sexual transmission and propagation of SIV and HIV in resting and activated CD4+ T cells. Science 1999; 286: 1353–1357. 79 Turville SG, Aravantinou M, Miller T, Kenney J, Teitelbaum A, Hu L et al. Efficacy of Carraguard-based microbicides in vivo despite variable in vitro activity. PLoS ONE 2008; 3: e3162. 80 Van Damme L, Govinden R, Mirembe FM, Guedou F, Solomon S, Becker ML et al. Lack of effectiveness of cellulose sulfate gel for the prevention of vaginal HIV transmission. N Engl J Med 2008; 359: 463–472. 81 Wilkinson D. Nonoxynol-9 fails to prevents STDs, but microbicide research continues. Lancet 2002; 360: 962–963. 82 Moszynski P. Halt to microbicide trial sets back AIDS research. BMJ 2007; 334: 276. 83 Steinbrook R. One step forward, two steps back—will there ever be an AIDS vaccine? N Engl J Med 2007; 357: 2653–2655. 84 Hladik F, Sakchalathorn P, Ballweber L, Lentz G, Fialkow M, Eschenbach D et al. Initial events in establishing vaginal entry and infection by human immunodeficiency virus type-1. Immunity 2007; 26: 257–270. 85 Miller CJ, Hu J. T cell-tropic simian immunodeficiency virus (SIV) and simian-human immunodeficiency viruses are readily transmitted by vaginal inoculation of rhesus macaques, and Langerhans’ cells of the female genital tract are infected with SIV. J Infect Dis 1999; 179 (Suppl 3): S413–S417. 86 Turville SG, Cameron PU, Handley A, Lin G, Pohlmann S, Doms RW et al. Diversity of receptors binding HIV on dendritic cell subsets. Nat Immunol 2002; 3: 975–983. 87 Geijtenbeek TB, Kwon DS, Torensma R, van Vliet SJ, van Duijnhoven GC, Middel J et al. DC-SIGN, a dendritic cell-specific HIV-1-binding protein that enhances transinfection of T cells. Cell 2000; 100: 587–597. 88 Turville SG, Arthos J, Donald KM, Lynch G, Naif H, Clark G et al. HIV gp120 receptors on human dendritic cells. Blood 2001; 98: 2482–2488. 89 de Witte L, Bobardt M, Chatterji U, Degeest G, David G, Geijtenbeek TB et al. Syndecan-3 is a dendritic cell-specific attachment receptor for HIV-1. Proc Natl Acad Sci USA 2007; 104: 19464–19469.

Viruses and Langerhans cells AL Cunningham et al 423 90 Kawamura T, Gulden FO, Sugaya M, McNamara DT, Borris DL, Lederman MM et al. R5 HIV productively infects Langerhans cells, and infection levels are regulated by compound CCR5 polymorphisms. Proc Natl Acad Sci USA 2003; 100: 8401–8406. 91 de Witte L, Nabatov A, Pion M, Fluitsma D, de Jong MA, de Gruijl T et al. Langerin is a natural barrier to HIV-1 transmission by Langerhans cells. Nat Med 2007; 13: 367–371. 92 Turville SG, Santos JJ, Frank I, Cameron PU, Wilkinson J, Miranda-Saksena M et al. Immunodeficiency virus uptake, turnover, and 2-phase transfer in human dendritic cells. Blood 2004; 103: 2170–2179. 93 Yu HJ, Reuter MA, McDonald D. HIV traffics through a specialized, surface-accessible intracellular compartment during trans-infection of T cells by mature dendritic cells. PLoS Pathog 2008; 4: e1000134. 94 van der Vlist M, Geijtenbeek TBH. Langerin fuctions as an antiviral receptor on Langerhans cells. Immunol and Cell Biol 2010; 88: 410–415. 95 Kawamura T, Koyanagi Y, Nakamura Y, Ogawa Y, Yamashita A, Iwamoto T et al. Significant virus replication in Langerhans cells following application of HIV to abraded skin: relevance to occupational transmission of HIV. J Immunol 2008; 180: 3297–3304. 96 Cunningham AL, Harman AN, Donaghy H. DC-SIGN ‘AIDS’ HIV immune evasion and infection. Nat Immunol 2007; 8: 556–558. 97 McDonald D, Wu L, Bohks SM, KewalRamani VN, Unutmaz D, Hope TJ. Recruitment of HIV and its receptors to dendritic cell-T cell junctions. Science 2003; 300: 1295–1297. 98 Turville SG, Aravantinou M, Stossel H, Romani N, Robbiani M. Resolution of de novo HIV production and trafficking in immature dendritic cells. Nat Methods 2008; 5: 75–85. 99 Fahrbach KM, Barry SM, Ayehunie S, Lamore S, Klausner M, Hope TJ. Activated CD34-derived Langerhans cells mediate transinfection with human immunodeficiency virus. J Virol 2007; 81: 6858–6868. 100 Frank I, Piatak Jr M, Stoessel H, Romani N, Bonnyay D, Lifson JD et al. Infectious and whole inactivated simian immunodeficiency viruses interact similarly with primate dendritic cells (DCs): differential intracellular fate of virions in mature and immature DCs. J Virol 2002; 76: 2936–2951. 101 Frank I, Stossel H, Gettie A, Turville SG, Bess Jr JW, Lifson JD et al. A fusion inhibitor prevents spread of immunodeficiency viruses, but not activation of virus-specific T cells, by dendritic cells. J Virol 2008; 82: 5329–5339. 102 Garcia E, Pion M, Pelchen-Matthews A, Collinson L, Arrighi JF, Blot G et al. HIV-1 trafficking to the dendritic cell-T-cell infectious synapse uses a

103

104 105

106

107

108

109

110 111

112

113

114

115

pathway of tetraspanin sorting to the immunological synapse. Traffic 2005; 6: 488–501. Wang JH, Janas AM, Olson WJ, Wu L. Functionally distinct transmission of human immunodeficiency virus type 1 mediated by immature and mature dendritic cells. J Virol 2007; 81: 8933–8943. Krementsov DN, Weng J, Lambele M, Roy NH, Thali M. Tetraspanins regulate cell-tocell transmission of HIV-1. Retrovirology 2009; 6: 64. Weng J, Krementsov DN, Khurana S, Roy NH, Thali M. Formation of syncytia is repressed by tetraspanins in human immunodeficiency virus type 1-producing cells. J Virol 2009; 83: 7467–7474. Cavrois M, Neidleman J, Kreisberg JF, Fenard D, Callebaut C, Greene WC. Human immunodeficiency virus fusion to dendritic cells declines as cells mature. J Virol 2006; 80: 1992–1999. Peng G, Greenwell-Wild T, Nares S, Jin W, Lei KJ, Rangel ZG et al. Myeloid differentiation and susceptibility to HIV-1 are linked to APOBEC3 expression. Blood 2007; 110: 393–400. de Jong MA, de Witte L, Oudhoff MJ, Gringhuis SI, Gallay P, Geijtenbeek TB. TNFalpha and TLR agonists increase susceptibility to HIV-1 transmission by human Langerhans cells ex vivo. J Clin Invest 2008; 118: 3440–3452. Ogawa Y, Kawamura T, Kimura T, Ito M, Blauvelt A, Shimada S. Gram-positive bacteria enhance HIV-1 susceptibility in Langerhans cells, but not in dendritic cells, via Tolllike receptor activation. Blood 2009; 113: 5157–5166. Douek DC, Brenchley JM, Betts MR, Ambrozak DR, Hill BJ, Okamoto Y et al. HIV preferentially infects HIV-specific CD4+ T cells. Nature 2002; 417: 95–98. Lore K, Smed-Sorensen A, Vasudevan J, Mascola JR, Koup RA. Myeloid and plasmacytoid dendritic cells transfer HIV-1 preferentially to antigen-specific CD4+ T cells. J Exp Med 2005; 201: 2023–2033. Harman AN, Wilkinson J, Bye CR, Bosnjak L, Stern JL, Nicholle M et al. HIV induces maturation of monocyte-derived dendritic cells and Langerhans cells. J Immunol 2006; 177: 7103–7113. Smed-Sorensen A, Lore K, Vasudevan J, Louder MK, Andersson J, Mascola JR et al. Differential susceptibility to human immunodeficiency virus type 1 infection of myeloid and plasmacytoid dendritic cells. J Virol 2005; 79: 8861–8869. Wilflingseder D, Mullauer B, Schramek H, Banki Z, Pruenster M, Dierich MP et al. HIV-1-induced migration of monocyte-derived dendritic cells is associated with differential activation of MAPK pathways. J Immunol 2004; 173: 7497–7505. Bosnjak L, Jones CA, Abendroth A, Cunningham AL. Dendritic cell biology in herpesvirus infections. Viral Immunol 2005; 18: 419–433.
