AIDS RESEARCH AND HUMAN RETROVIRUSES Volume 16, Number 1, 2000, pp. 19–25 Mary Ann Liebert, Inc.
Short Communication Influenza Virus Upregulates CXCR4 Expression in CD4 1 Cells ANU PURI,1 JAMES L. RILEY,2 DANIEL KIM, 3 DAVID W. RITCHEY, 3 PETER HUG,1 KRISTINE JERNIGAN,1 PATRICK ROSE,1 ROBERT BLUMENTHAL, 1 and RICHARD G. CARROLL 3,4
ABSTRACT We examined the effect of prior influenza virus infection on the susceptibility of CD4 1 cells to HIV-1 infection. Influenza virus infection of HeLa-CD4 cells resulted in a marked increase in susceptibility to infection by CXCR4-dependent but not CCR5-dependent HIV isolates. Influenza virus infection resulted in an increase in the steady state level of CXCR4 transcripts and an increase in cell surface CXCR4 expression. Our observations suggest that infectious agents such as influenza may contribute to HIV disease progression by modulating coreceptor availability.
H
HIV-1N L4-3 INFECTION OF HeLa-CD4 CELLS IS ENHANCED BY PRIOR INFECTION WITH INFLUENZA VIRUS
disease progression is characterized by declining immune function, which renders infected individuals susceptible to a variety of opportunistic infections. 1 We undertook this study to examine how other infectious agents can modulate the susceptibility of cells to subsequent HIV infection. In this article we exam ine the effect of a common pathogen, influenza virus, on the replicative ability of HIV-1. HeLa-CD4 cells were first infected with influenza virus, and then infected with either a CCR5-dependent (R5) or a CXCR4dependent (X4) HIV isolate. R5 HIV isolates are implicated in transmission of HIV-12 ,3 ; they primarily use the b -chemokine receptor CCR5 to infect CD41 T cells. 4–8 X4 HIV isolates are obtained from later stage individuals; they employ the a chemokine receptor CXCR4 as a coreceptor. 9 We report that after influenza virus infection, there is a marked boost in replication of X4 HIV isolates; this increased X4 susceptibility correlates the upregulation of cellular CXCR4 expression. Therefore, our results suggest that infectious agents such as influenza virus may impact HIV disease progression by increasing the susceptibility of cells to HIV-1 infection. U M A N IM M U N O D EFICIEN C Y V IR U S
The effect of influenza virus infection on subsequent HIV1 susceptibility was assayed by first infecting HeLa-CD4 cells with influenza virus strain A/PR/8 for 8–16 hr. Uncleaved influenza hemagglutinin (HA) precursor (HA0) was then converted to fusion active HA by a brief exposure to trypsin. 10 Forty to 60% of HeLa-CD4 cells became infected with influenza virus (data not shown), as determined by monitoring the binding of human erythrocytes to cell surface-expressed influenza HA.1 1 After influenza infection, HeLa-CD4 cells were infected with the X4 isolate HIV N L4-3 12 and the progress of infection was monitored with a polymerase chain reaction (PCR)based assay that detects nearly full-length reverse-transcribe d (gag) HIV DNA.13,14 Infected cell supernatants were also monitored for the presence of HIV p24 gag antigen by enzym e-linked immunosorbe nt assay (ELISA) (Coulter, Miami, FL). HeLa-CD4 cells are susceptible to HIV N L4-3 infection in the absence of influenza virus infection (Fig. 1A). However, prior
1 NCI-FCRDC,
Frederick, Maryland 21702. of Retrovirology, Walter Reed Army Institute for Research, Rockville, Maryland 20850. 3 Henry M. Jackson Foundation for the Advancement of Military Medicine, U.S. Military HIV Research Program, Bethesda, Maryland 20889. 4 Present address: Stellar Chance Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania 19104. 2 Division
19
20
PURI ET AL.
influenza virus infection resulted in a marked increase (greater than 10-fold) in the amount of HIV gag DNA detected within HeLa-CD4 cells (Fig. 1A). DNA standards were run and the amount of template DNA was adjusted so that a linear dose–response relationship was maintained. 15 Furthermore, HIV p24 gag antigen production by HeLa-CD4 cells was strongly elevated by prior influenza infection, and the influenza-enhanced p24 gag production was maintained for 6 days after HIV infection (Fig. 1B). Neither HIV gag DNA nor p24 gag production was observed when HeLa cells lacking CD4 were HIV infected, either in the presence or absence of prior influenza infection (data not shown). These experiments demonstrate that influenza-infected HeLa-CD4 cells are highly susceptible to HIV-1 infection, and that expression of CD4 on the HeLa cell surface is required for enhanced infection.
We next examined early steps in the HIV replication cycle by monitoring reverse transcription in influenza-infected HeLaCD4 cells. HeLa-CD4 cells used in this study were only permissive to fusion mediated by HIV-1 (X4) envelope glycoprotein-expressing cells. These cells do not show any fusion with the cells expressing an R5 HIV-1 (Ba-L) envelope glycoprotein-expressing cells. PCR was performed with primers designed to detect early reverse transcription products synthesized before the first strand switch (“strong-stop” DNA).15,16 As shown in Fig. 2, enhanced synthesis of strong-stop DNA in influenza-infected cells was detected as early as 2 hr postinfection. Twenty-four hours after HIV infection, influenza-infected HeLa-CD4 cells contained greater than 10 times more HIV strong-stop DNA than the mock influenza-infected controls. The rapid increase in the copy number of early reverse transcription
A
B
FIG. 1. Prior influenza virus infection enhances susceptibility of HeLa-CD4 cells to HIV N L 4-3 . (A) Production of HIV reverse transcripts in influenza-infected HeLa-CD4 cells. HeLa-CD4 cells were infected with influenza virus strain A/PR/8 and incubated for 8–16 hr at 37°C. The cells were then infected with 3 3 10 4 TCID 50 (50% tissue culture infectious doses) of HIV N L4-3 for 2 hr. Cells were harvested immediately after virus addition (hour 0), postvirus washout (hour 2), and at designated time points thereafter. Cell lysates were analyzed by DNA PCR for the presence of HIV gag reverse transcripts. Lysates were also PCR amplified with hum an b -globin primers, to control for the cellular DNA input level. Amplified products were annealed with endlabeled oligonucleotide probes and separated on polyacrylamide gels. Products were visualized with a PhosphorImag er (model 445SI; Molecular Dynam ics, Sunnyvale, CA). Images were generated by ImageQuant software (Molecular Dynamics). Shown are representative results from one of five independent experiments. P.I., Postinfection. (B) Analysis of HIV p24 gag antigen production in influenza-infected HeLa-CD4 cells. HeLa-CD4 cells were infected with HIV N L4 -3 as described in (A). Supernatants were harvested at the indicated times after HIV infection, and p24 gag antigen levels were determined by ELISA. Filled sym bols denote cells previously infected with influenza virus, while open sym bols denote mock influenza-infected cells. Representative values from one of three experiments are depicted.
CXCR4 UPREGULATION BY INFLUENZA VIRUS
21 products in influenza-infected cells suggested that prior influenza infection acted to accelerate the process of HIV entry.
INFLUENZA VIRUS SELECTIVELY ENHANCES REPLICATION OF X4-UTILIZING HIV-1
FIG. 2. Early steps in HIV reverse transcription are enhanced in influenza virus-infected HeLa-CD4 cells. HeLa-CD4 cells were infected with influenza virus strain A/PR/8 or mock infected as described in the caption to Fig. 1. They were then infected with HIV N L4 -3 , and cells were harvested immediately after virus addition (hour 0), postvirus washout (hour 2), and 24 hr after HIV infection. Cell lysates were analyzed by DNA PCR for the presence of early (“strong stop”) HIV reverse transcripts. Lysates were also PCR amplified with hum an b -globin primers. Amplified products were detected as described in the caption to Fig. 1. Representative results from one of three experim ents are shown. P.I., Postinfection.
HIV disease progression is often accompanied by a shift in the phenotype of the infecting viruses. R5 isolates predominate during the early stages of disease, while X4 isolates are detected only during later disease stages. 2,3 We wished to determine whether the influenza-mediat ed increase in permissiveness to infection with the X4 isolate HIV N L 4-3 could also be observed with an R5 HIV-1 isolate. Accordingly, HeLa-CD4 cells were first infected with influenza virus as described above, and then infected with the R5 HIV-1 isolate HIV U S 1 .17 HIV U S 1 , a patient isolate, was originally characterized by Mascola et al. 17 HeLa-CD4 cells, which express CXCR4 but not CCR5 on their surface, are susceptible only to X4-utilizing HIV-1 isolates. When HeLa-CD4 cells were infected with HIV U S 1 , no HIV gag DNA was detected (Fig. 3). Furtherm ore, previous influenza infection of HeLa-CD4 cells, which greatly increased
FIG. 3. Influenza-media ted enhancement of HIV infection is restricted to X4 HIV-1 isolates. HeLa-CD4 cells were either mock influenza virus infected (A) or infected with influenza virus strain A/PR/8 (B). Subsequently, the cells were mock infected (—), or infected with 3 3 10 4 TCID 50 of the X4 isolate HIV N L4-3 or the R5 HIV isolate HIV U S 1 . Cells were harvested immediately after virus addition (hour 0), immediately postinfection (hour 2), and at indicated time points thereafter. HIV gag DNA levels in cell lysates were analyzed by PCR. All cell lysates were also PCR amplified with human b -globin primers. Shown are representative results from one of three independent experim ents. P.I., Postinfection.
22
PURI ET AL.
their susceptibility to the X4 isolate HIV N L4-3 , failed to render HeLa-CD4 cells perm issive for infection with the R5 isolate HIV U S 1 . These observations suggest that, at least in HeLa-CD4 cells, the influenza-mediat ed enhancement of HIV infection is restricted to X4 isolates of HIV-1.
INFLUENZA VIRUS INFECTION UPREGULATES CXCR4 EXPRESSION The X4 isolate-restricted enhancement of HIV infection by influenza virus suggested that in HeLa-CD4 cells, influenza
virus infection altered expression of coreceptors required for use by X4 viruses, but did not alter coreceptor expression for R5 isolates. Accordingly, expression of the X4 coreceptor CXCR4 and the R5 coreceptor CCR5 was examined in influenza-infected HeLa-CD4 cells. RNA was prepared from mock influenza-infected HeLa-CD4 cells and HeLa-CD4 cells at 8- and 24-hr intervals after influenza infection, and transcripts encoding CXCR4 and CCR5 were analyzed by a previously described reverse transcriptase (RT)-PCR technique 1 8,19 (Fig. 4A). CXCR4 transcripts were detectable in HeLa-CD4 cells in the absence of influenza detection, and their level increased ap-
A
B
FIG. 4. Influenza virus infection increases levels of CXCR4 expression. HeLa-CD4 cells were infected with influenza virus A/PR/8 as described in the caption to Fig. 1, and the infected cells were analyzed for expression of HIV coreceptors. (A) Measurement of HIV coreceptor transcript levels. At the designated hour after influenza infection, RNA was isolated and cDNA was prepared by reverse transcription. The cDNA products were diluted to predetermined optim al levels, and twofold serial dilutions (2.5, 5, and 10 m l) of the cDNA product were used for PCR amplification with primer pairs specific for CCR5, CXCR4, and glyceraldehyde-3-p hosphate dehydrogenase (GAPDH). M, PCR amplifications from mock influenzainfected cultures; 2 , reactions in which 10- m l aliquots from control cDNA synthesis reactions performed in the absence of reverse transcriptase were PCR amplified. Data shown are representative of two experiments. (B) Measurement of CXCR4 cell surface expression. Mock-infected or influenza-infected HeLa-CD4 cells were stained with influenza HA MAb and PEconjugated CXCR4 MAb. Flow cytometric analysis was performed with a FACScan (Becton Dickinson). Solid lines depict mock influenza-infected cells, while dotted lines represent influenza-infected cells. Filled curves indicate staining with isotype control antibodies.
CXCR4 UPREGULATION BY INFLUENZA VIRUS proximately sevenfold 8 hr after influenza infection. This increase in CXCR4 transcript level was transient. Twenty-four hours after influenza infection, the level of CXCR4 transcripts declined substantially, although it was still approximately threefold higher than the baseline level observed in uninfected HeLaCD4 cells. In contrast to these observations, we failed to detect CCR5 transcripts in either influenza-infected or uninfected HeLa-CD4 cells. CXCR4 surface expression after influenza virus infection was monitored by fluorescence-activ ated cell sorting (FACS) analysis and immunostaini ng. For FACS analysis, influenza-infected or mock-infected HeLa-CD4 cells were first incubated with an anti-influenza HA monoclonal antibody (MAb) (type A, H1N1 subtype, 1:50 dilution; Advanced Immuno Chemical, Long Beach, CA) followed by incubation with fluorescein isothiocyanate (FITC)-conju gated mouse MAb (Sigma, St. Louis, MO). Unbound antibody was rem oved and cells were incubated with R-phycoerythrin (R-PE)-conju gated CXCR4 MAb 12G5 20 (1:50 dilution; PharM ingen, San Diego, CA). Flow cytometric analysis was perform ed on fixed cells with a FACScan (Becton Dickinson, San Jose, CA). As shown in Fig. 4B, influenza infection resulted in a strong upregulation of CXCR4 expression, compared with mock influenza-infected cells. CXCR4 upregulation was further examined by immunostaining (Fig. 5). Influenza-infected or mock-infected HeLa-CD4 cells were stained with anti-HA MAb and antiCXCR4 MAb, essentially as described above. Phase and fluorescence images were captured with a X60 oil objective and an Olympus (Norwood, MA) 1X70 inverted microscope attached to a cooled charge-coupled device (CCD) camera (Princeton Instruments, Trenton, NJ). U-MNG filter cube and a U-MNIBA filter cube were used to visualize PE and FITC fluorescence, respectively. CXCR4 expression on the surface of influenza-infected HeLa-CD4 cells was significantly enhanced compared with mock-infected controls. It is interesting that CXCR4 upregulation was observed only in cells that expressed influenza HA (indicated by arrow, Fig. 5), indicating that influenza virus
23 infection was required in cis for the observed upregulation to occur. These observations indicate that influenza virus specifically upregulates CXCR4 expression, providing a mechanism for the observed increased susceptibility of influenza-infected HeLa-CD4 cells to X4 HIV-1 isolates. Influenza infection is characterized by strong shifts in cytokine and b -chemokine production. 21–25 It is tempting to speculate that the altered levels of cytokines or chemokines engendered by influenza infection act to increase CXCR4 expression. Indeed, CXCR4 surface expression is increased by interleukin 4 (IL-4) addition, 26,27 and b -chem okines increase X4 HIV isolate entry and replication in CD41 T cells. 28 However, we have dem onstrated (Fig. 5) that CXCR4 expression increases only in cells that coexpress influenza proteins. This argues against a trans-acting, diffusible cytokine/ chemokine-depe ndent mechanism, and suggests that a more direct influenza-m ediated mechanism may be responsible for increased CXCR4 expression. In this light, it is noteworthy that expression of the influenza HA gene product activates NF-k B in HeLa cells. 29 A rapidly accumulating body of evidence indicates that a complex series of interactions between coinfecting pathogens may modify the outcome of HIV infection. Since optimal HIV infection requires activated CD41 lymphocytes, 30 it is conceivable that any event that results in increased immune activation increases the number of potential HIV target cells and hence may indirectly accelerate virus spread. Alternatively, coinfecting agents may directly alter the susceptibility of target cells to HIV infection, and any agent that triggers increased coreceptor expression could be viewed as a potential accelerator of HIV pathogenesis. In macrophages, Mycobacterium avium infection induces high-level CCR5 surface expression, 31 and exposure to bacterial cell wall products enhances their susceptibility to X4 HIV-1 isolates. 32 In addition, HTLV-I-triggered b -chemokine production increases the sensitivity of CD41 T cells to X4 HIV1 isolates. 33 The data presented herein demonstrate that influenza virus, by increasing CXCR4 expression (in cis), significantly enhances subsequent HIV-1 infection.
FIG. 5. CXCR4 upregulation is confined to influenza-infected cells. HeLa-CD4 cells were mock influenza infected or infected with influenza virus. The cells were then incubated with anti-influenza HA antibodies and anti-CXCR4 antibodies as described in Fig. 4B. Phase and fluorescence images (60 3 oil objective) are depicted. Cells expressing influenza HA are indicated by arrows in phase pictures.
24
PURI ET AL.
ACKNOWLEDGMENTS HeLa-CD4 cells were the kind gift of Dr. John Silver (NIAID, Bethesda, MD). This study was supported in part by Army Contract DAMD17-93-V-300 4 and by the Henry M. Jackson Foundation, and by the Intramural AIDS Targeted Antiviral Program.
REFERENCES 1. Pantaleo G and Fauci A: New concepts in the immunopathogen esis of HIV infection. Annu Rev Immunol 1995;13:487– 512. 2. Connor RI, Sheridan KE, Ceradini D, Choe S, and Landau NR: Change in coreceptor use correlates with disease progression in HIV-1-infected individuals. J Exp Med 1997;185:621– 628. 3. Scarlatti G, Tresoldi A, Bjorndal A, Fredriksson R, Colognesi C, Deng H, Malnatti MS, Plebani A, Siccardi AG, Littman DR, Fenyo EM, and Lusso P: In vivo evolution of HIV-1 coreceptor usage and sensitivity to chemokine-me diated suppression. Nature Med 1997; 3:1259– 1265. 4. Alkhatib G, Combadiere C, Broder CC, Feng Y, Kennedy PE, Murphy PM, and Berger EA: CC CKR5:ARANTES, MIP-1alpha, MIP-1beta receptor as a fusion cofactor for macrophage-t ropic HIV-1. Science 1996;272:1955– 1958. 5. Choe H, Farzan M, Sun Y, Sullivan N, Rollins B, Ponath PD, Wu L, Mackay CR, LaRosa G, Newman W, Gerard N, Gerard C, and Sodroski J: The beta-chemokine receptors CCR3 and CCR5 facilitate infection by primary HIV-1 isolates. Cell 1996;85:1135– 1148. 6. Deng H, Liu R, Ellmeier W, Choe S, Unutmaz D, Burkhart M, Di Marzio P, Marmon S, Sutton RE, Hill CM, Davis CB, Peiper SC, Schall TJ, Littman DR, and Landau NR: Identification of a major co-receptor for primary isolates of HIV-1. Nature (London) 1996; 381:661– 666. 7. Doranz BJ, Rucker J, Yi Y, Smyth RJ, Samson M, Peiper SC, Parmentier M, Collman RG, and Doms RW: A dual-tropic primary HIV-1 isolate that uses fusin and the beta-chemokine receptors CKR-5, CKR-3, and CKR-2b as fusion cofactors. Cell 1996;85: 1149– 1158. 8. Dragic T, Litwin V, Allaway GP, Martin SR, Huang Y, Nagashima KA, Cayanan C, Maddon PJ, Koup RA, Moore JP, and Paxton WA: HIV-1 entry into CD41 cells is mediated by the chemokine receptor CC-CKR-5. Nature (London) 1996;381:667– 673. 9. Feng Y, Broder CC, Kennedy PE, and Berger EA: HIV-1 entry cofactor: Functional cDNA cloning of a seven-transmembrane, G protein-coupled receptor. Science 1996;272:872– 877. 10. Pak CC, Krumbiegel M, Blumenthal R, and Raviv Y: Detection of influenza hemagglutinin interaction and biological membranes by photosensitized activation of [125 I]iodonaphthylaz ide. J Biol Chem 1994;269:14614– 14619. 11. Puri A, Booy F, Doms RW, White JM, and Blumenthal R: Conformational changes and fusion activity of influenza hemagglutinin of the H2 and H3 subtypes: Effects of acid pretreatment. J Virol 1990;64:3824– 3832. 12. Adachi A, Gendelman HE, Koenig S, Folks T, Willey R, Rabson A, and Martin MA: Production of acquired immunodeficie ncy syndrome-associated retrovirus in human and nonhuman cells transfected with an infectious molecular clone. J Virol 1986;59:284– 291. 13. Vahey MT and Wong MT: Quantitative liquid hybridization PCR method employing storage phosphor technology. In: PCR Primer: A Laboratory Manual (Dieffenbach CW and Dveksler GS, eds.). Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, 1995, pp. 313–338.
14. Levine BL, Mosca J, Riley JL, Carroll RG, Vahey MT, Jagodzinski KF, Wagner KF, Mayers DL, Burke DS, Weislow OS, St Louis DC, and June CH: Antiviral effect and ex vivo CD4 1 T cell proliferation in HIV-positive patients as a result of CD28 costimulation. Science 1996;272:1939– 1943. 15. Carroll RG, Riley JL, Levine BL, Feng Y, Kaushal S, Richey DW, Bernstein W, Weislow OS, Brown CR, Berger EA, June CH, and St Louis, DC: Differential regulation of HIV-1 fusion cofactor expression by CD28 costimulation of CD4 1 T cells. Science 1997; 276:273– 276. 16. Zack JA, Arringo SJ, Weitsman SR, Go AS, Haislip A, and Chen IS: HIV-1 entry into quiescent primary lymphocytes: Molecular analysis reveals a labile, latent viral structure. Cell 1990;61:213– 222. 17. Mascola JR, Louwagie J, McCutchan FE, Fischer CL, Hegerich PA, Wagner KF, Flower AK, McNeil JG, and Burke DS: Two antigenically distinct subtypes of human immunodeficie ncy virus type 1: Viral genotype predicts neutralization serotype. J Infect Dis 1994;169:48– 54. 18. Riley JL, Levine BL, Craighead N, Francomano T, Kim D, Carroll RG, and June CH: Naive and memory CD4 T cells differ in their susceptibilities to human immunodeficie ncy virus type 1 infection follow ing CD28 costimulation: Implications for transmission and pathogenesis. J Virol 1998;72:8273– 8280. 19. Riley JL and Carroll RG: Quantitation of HIV-1 entry cofactor expression. In: HIV Protocols (Michael NL and Kim JH, eds.). Humana Press, Totowa, New Jersey, 1998. 20. Endres MJ, Clapham PR, Marsh M, Ahuja M, Turner JD, McKnight A, Thomas JF, Stoebenau-Ha ggarty B, Choe S, Vance PJ, Wells TN, Power CA, Sutterwala SS, Doms RW, Landau NR, and Hoxie JA: CD4-independe nt infection by HIV-2 is mediated by fusin/CXCR4. Cell 1996;87:745– 756. 21. Hayden FG, Fritz RS, Lobo WG, Alvord WG, Strober W, and Straus SE: Local and systemic cytokine responses during experimental human influenza A virus infection. Relation to symptom formation and host defense. J Clin Invest 1998;101:643– 649. 22. Peschke T, Bender A, Nain M, and Gemsa D: Role of macrophage cytokines in influenza A virus infections. Immunobiology 1993; 189:340– 355. 23. Sprenger H, Meyer RG, Kaufmann A, Bussfield D, Rischkowsky E, and Gemsa D: Selective induction of monocyte and not neutrophil-attractin g chemokines after influenza A virus infection. J Exp Med 1996;184:1191– 1196. 24. Matsukura S, Kokubu SF, Noda H, Tokunaga H, and Adachi M: Expression of IL-6, IL-8, and RANTES on human bronchial epithelial cells, NCI-H292, induced by influenza virus A. J Allergy Clin Immunol 1996;98:1080– 1087. 25. Matsukura S, Kokubu SF, Kubo H, Tromita T, Tokunaga H, Kadokura T, Yamamoto T, Kuroiwa Y, Ohno T, Suzaki H, and Adachi M: Expression of RANTES by normal airway epithelial cells after influenza virus A infection. Am J Respir Cell Mol Biol 1998;18:255– 264. 26. Jourdan P, Abbal C, Nora N, Hori T, Uchiyama T, Vendrell JP, Bousquet J, Taylor N, Pene J, and Yssel H: IL-4 induces functional cell-surface expression of CXCR4 on human T cells. J Immunol 1998;160:4153– 4157. 27. Valentin A, Lu W, Rosati M, Schneider R, Albert J, Karlsson A, and Pavlakis GN: Dual effect of interleukin 4 on HIV-1 expression: implications for viral phenotypic switch and disease progression. Proc Natl Acad Sci USA 1998;95:8886– 8891. 28. Kinter A, Catanzaro A, Monaco J, Ruiz M, Justement J, Moir S, Arthos J, Oliva A, Ehler L, Mizell S, Jackson R, Ostrowski M, Hoxie JA, Offord R, and Fauci A: CC-chemokine s enhance the replication of T-tropic strains of HIV-1 in CD4( 1 ) T cells: Role of signal transduction. Proc Natl Acad Sci USA 1998;95: 11880–11885.
CXCR4 UPREGULATION BY INFLUENZA VIRUS 29. Pahl HL and Baeuerle PA: Expression of influenza virus hemagglutinin activates transcription factor NF-kappa B. J Virol 1995; 69:1480– 1484. 30. Chou CS, Ramilio O, and Vitetta ES: Highly purified CD25- resting T cells cannot be infected de novo with HIV-1. Proc Natl Acad Sci USA 1997;94:1361– 1365. 31. Wahl SM, Greenwell-Wild T, Peng G, Hale-Donze H, Doherty TM, Mizel D, and Orenstein JM: Mycobacterium avium complex augments macrophage HIV-1 production and increases CCR5 expression. Proc Natl Acad Sci USA 1998;95:12574– 12579. 32. Moriuchi M, Moriuchi H, Turner W, and Fauci A: Exposure to bacterial products renders macrophages highly susceptible to Ttropic HIV-1. J Clin Invest 1998;102:1540– 1550. 33. Moriuchi H, Moriuchi M, and Fauci A: Factors secreted by human T lymphotropic virus type I (HTLV-I)-infected cells can enhance
25 or inhibit replication of HIV-1 in HTLV-I-uninfected cells: Implications for in vivo coinfection with HTLV-I and HIV-1. J Exp Med 1998;187:1689– 1697.
Address reprint requests to: Anu Puri Laboratory of Experimental and Computationa l Biology NCI-FCRDC P.O. Box B, Bldg. 469, Rm. 211 Miller Drive Frederick, Maryland 21702-1201 E-mail:
[email protected]. gov
