Chlamydial Lipopolysaccharide - Infection and Immunity - American ...

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for their help in establishing the hybridoma technology. This work was supported by the Bundesministerium fur Fors- chung und Technologie (grant 01 ZR 8604 ...

Vol. 58, No. 1

INFECTION AND IMMUNITY, Jan. 1990, p. 205-213 0019-9567/90/010205-09$02.00/0 Copyright © 1990, American Society for Microbiology

Characterization of Murine Monoclonal and Murine, Rabbit, and Human Polyclonal Antibodies against Chlamydial Lipopolysaccharide LORE BRADE,' OTTO HOLST,1 PAUL KOSMA,2 YOU-XUN ZHANG,3t HANS PAULSEN,4 REA KRAUSSE,5 AND HELMUT BRADE1* Division of Biochemical Microbiology, Institut fur Experimentelle Biologie und Medizin, Forschungsinstitut Borstel, Parkallee 22, D-2061 Borstel, Federal Republic of Germany1; Institut fur Chemie der Universitat fur Bodenkultur, A-i 180 Vienna, Austria2; Laboratory of Microbial Structure and Function, Rocky Mountain Laboratory, Hamilton, Montana 598403; Institut fur Organische Chemie der Universitat, D-2000 Hamburg, Federal Republic of Germany 4; and Abteilung fur Medizinische Mikrobiologie der Universitat, D-2100 Kiel, Federal Republic of Germany5 Received 10 July 1989/Accepted 19 September 1989 Murine monoclonal and rabbit, murine, and human polyclonal antibodies against chlamydial lipopolysaccharide (LPS) were characterized by the passive hemolysis and passive hemolysis inhibition assays and by absorption experiments with LPSs of Chlamydia psittaci, Chlamydia trachomatis, and a recombinant strain of Salmonella minnesota Re (r595-207) expressing the chlamydia-specific LPS epitope, as well as natural and synthetic partial structures of chlamydial LPS. Eleven monoclonal antibodies of the immunoglobulin M and G classes were characterized as chlamydia-specific by their failure to react with Re-type LPS, binding to a similar epitope for which the trisaccharide a-3-deoxy-D-manno-2-octulosonic acid (KDO)-(2-8)-a-KDO-(2-4)-CL-KDO was an absolute prerequisite. For optimal binding, parts of the lipid A moiety were also involved; however, phosphoryl and ester-linked acyl groups and the reducing glucosamine residue of lipid A were dispensable. A similar antibody specificity was detected in lapine and murine hyperimmune sera after immunization with chlamydia, in addition to those recognizing more complex (e.g., those requiring the presence of phosphoryl residues) and less complex epitopes. Among the latter were those cross-reacting with Re-type LPS, which could be removed by absorption. The titers of different antibody specificities, in particular the ratio of chlamydiaspecific to cross-reactive antibodies, present in murine polyclonal antisera depended on the immunization protocol. The preferential formation of chlamydia-specific antibodies was observed after immunization with liposome-incorporated immunogens. Human sera from patients with suspected genital chlamydial infections were also found to contain chlamydia-specific and cross-reactive antibodies, the latter of which could be removed by absorption with Re-type LPS.

Such antibodies also react with chlamydial LPS (1) and are obviously present in polyclonal anti-chlamydia antisera, thus causing their cross-reaction with Re-type LPS. In addition, monoclonal and polyclonal antibodies which recognize the chlamydia-specific LPS epitope and do not cross-react with Re-type LPS have been described (7, 9, 10, 20). We found that chlamydial LPS contains a linear KDO trisaccharide of the sequence (x-KDO-(2-8)-a-KDO-(2-4)KDO, in which the oa-2,8-linked disaccharide portion was assumed to represent the immunodominant region of the genus-specific epitope (1, 16). In the meantime, we have prepared a variety of synthetic compounds and chemically defined partial structures of LPS which can be used as antigens to characterize chlamydial LPS antibodies. Here we report on our results obtained with murine monoclonal antibodies and polyclonal antisera from mice, rabbits, and

Chlamydiae are pathogenic, obligatory intracellular parasites causing a variety of diseases in animals and humans. Little is known about molecular mechanisms of pathogenicity of these unique microorganisms and the host defense mechanisms against them. Surface structures of chlamydiae are involved in the early steps during infection (adhesion and penetration), and these at the same time are surface antigens against which antibodies are raised during infection. It is known that chlamydiae possess a surface glycolipid antigen which harbors a genus-specific epitope containing an immunodominant sugar chemically related to 3-deoxy-Dmanno-2-octulosonic acid (KDO) (11, 12). Chemical studies on this antigen have shown that it contains typical chemotaxonomical markers for lipopolysaccharide (LPS), such as KDO, D-glucosamine, phosphorus, and long-chain 3-hydroxy fatty acids (9, 19). This composition is similar to that of LPS from enterobacterial Re mutants (8) and thus provides a basis to understand cross-reactions between chlamydiae and other bacterial species on the molecular level. Studies on monoclonal antibodies against the Re-type LPS, containing an a-2,4-linked KDO disaccharide in its saccharide portion, have shown that antibodies which recognize the KDO (5) or lipid A region (3) or both (22) can be selected.

humans. MATERIALS AND METHODS Bacteria and bacterial LPS. The Re mutant of Salmonella minnesota (strain R595) was transformed with plasmid pFEN207 (17) and propagated as described previously (6). LPS was extracted by the phenol-chloroform-petroleum ether method (14) and purified by repeated ultracentrifugation, followed by conversion to the uniform triethylammonium salt after electrodialysis (13). This LPS has been shown to contain the genus-specific epitope of chlamydial LPS (1);

* Corresponding author. t Permanent address: Beijing Institute of Ophthalmology, Beijing 100005, People's Republic of China.

205

206

INFECT. IMMUN.

BRADE ET AL. CONH2

CONH2

I I H-[(CH2-CH)x-CH2-CH-(CH2-CH)y]n-H CH20 - R

Compound

Nature of substituent

Amt (nmol) of ligand/

R =

mg of copolymerisate

(abbreviated) KDO-PA

KDO-(2 -e

323

2.4-KDO 2-PA

KD0-(2-.4)-KD0-(2--e

338

2.8-KDO 2-PA

KDO-(2- 8)-KDO-(2--"

295

2.8.4-KD03-PA KDO-(2--_8)-KDO-(2-e4)-KDO-(2-.,

106

FIG. 1. Synthetic copolymerization products used as antigens in this study. KDO-PA, KDO-polyacrylamide. Values were determined by the thiobarbiturate assay.

it will be referred to as r595-207 LPS. LPS was prepared in a similar way from an Escherichia coli Re mutant (strain F515). Chlamydial LPS of Chlamydia psittaci PK 5082 (23) and Chlamydia trachomatis serotype L2 were prepared as reported previously (9, 19). Preparation of LPS partial structures. Alkali-treated LPS (LPS-OH); de-O-acylated and dephosphorylated LPS (LPSHF); and de-O-acylated, dephosphorylated, and reduced LPS (LPS-HFr) were prepared as reported previously (22). Synthetic antigens. The copolymerization products listed in Fig. 1 were synthesized as described previously (15, 16). Sodium 3-deoxy-at-D-manno-2-octulopyranosylonate-(2---6)2 - deoxy - 2 - [(R) - 3 - hydroxytetradecanamido] - , - D- glucopyr-

anosyl-(1---6)-2-deoxy-2-[(R)-3-hydroxytetradecanamido]-Dglucose and disodium [3-deoxy-ot-D-manno-2-octulopyranosylonate - (2-*4) - 3 - deoxy - a - D - manno - 2 - octulopyranosylonate] - (2-6) - 2 - deoxy - 2 - [(R) - 3 - hydroxytetradecanamido] ,1- D-glucopyranoanosyl] -(1-+6)-2-deoxy-2- [(R) -3 -hydroxytetradecanamido]-D-glucose were synthesized as previously described (C. Krogmann, Ph.D. thesis, University of Hamburg, Hamburg, Federal Republic of Germany, 1989; 21). These compounds are partial structures of Re-type LPS containing the glucosamine backbone of lipid A with two amide-linked 3-hydroxymyristic acid residues and one or two KDO residues and will be abbreviated as KDOGlcNhm2 and KDO2-GlcNhm2, respectively. Preparation of immunogens. Liposome-incorporated immunogens were prepared as previously described (3). Heatkilled bacteria were prepared by boiling an overnight culture at 100°C for 1 h. Sheep erythrocyte (SRBC)-coated immunogens were prepared as described below by using 200 ,ug of antigen per 200 ,ul of SRBCs. Animal antisera. Rabbit antisera against heat-killed bacteria were prepared as described previously (6). Mouse antisera from female, 8- to 10-week-old BALB/c mice in groups of four were used. Antisera against heat-killed bacteria were prepared as described for rabbits; however, injections were done intraperitoneally. Sera against SRBC-coated and liposome-incorporated immunogens were obtained after five intraperitoneal injections of increasing amounts (20 to 50 ,ug) of antigen in a total volume of 200 ,ul of SRBCs or liposome suspension, respectively, over a 2-month period. The animals were then tested for the presence of antibodies against chlamydial LPS. The one with the highest titer was used for the preparation of monoclonal antibodies, whereas the oth-

ers were given a booster 3 months later and were exsanguinated 1 week after the last injection. Serology. (i) Passive hemolysis and passive hemolysis inhibition assays. The hemolysis test was carried out in 96-well microdilution plates. SRBCs were washed three times in phosphate-buffered saline. Packed cells (0.2 ml) in 5 ml of phosphate-buffered saline were mixed with graded amounts (1 to 200 ,ug) of the respective antigen and incubated at 37°C for 30 min with occasional shaking. The antigen-coated cells were washed three times in phosphate-buffered saline and finally suspended in 40 ml of Veronal-buffered saline (VBS) to give a 0.5% suspension. Serial twofold dilutions of antibody in VBS (50 pI) were mixed with 50 pul of antigen-coated SRBCs and 25 pul of guinea pig serum (prechecked for the absence of chlamydial LPS antibodies and diluted 1:20 in VBS) as a source of complement, followed by incubation at 37°C for 1 h. After centrifugation, 50% endpoint titers were determined. One hemolytic unit is defined as the amount of antibody causing 50% of hemolysis under these test conditions. The passive hemolysis inhibition test was performed by preincubating 3 to 4 hemolytic units of antibody in 25 pI of VBS with serial twofold dilutions of inhibitor in 25 ,ul of VBS at 37°C for 15 min. After the addition of antigen-coated SRBCs (50 pul) and 25 pu1 of complement, the plates were incubated at 37°C for 1 h. Inhibition values are expressed as amount of inhibitor causing 50% inhibition of hemolysis. (ii) Enzyme immunosorbent assay. Polyvinyl plates (96well, type 3911; Falcon Plastics) were coated with 50 1.l of a solution of LPS (4 p,g/ml) in phosphate-buffered saline (PBS) at 37°C overnight, followed by blocking in PBS containing 10% defatted dry milk at 37°C for 1 h. The following steps were done according to standard procedures. (iii) Absorption. Absorption was carried out at 4°C for 1 h on 500-pA samples of prediluted antisera (1:10 in PBS) with 50 pI of packed SRBCs coated with the respective antigen. Absorption with uncoated SRBCs served as a control. Monoclonal antibodies. The following clones were obtained after immunization with purified elementary bodies of C. psittaci PK 5082 (23) (clones S5-10 and S10-3) and C. trachomatis serotype L2 (clone L21-6), serotype E (clone EVI-Hl), serotype G (clones GIII-C3 and GII-B3), and serotype F (clones FVI-A4 and FI-A6). Clones S15-1, S15-2, and S15-6 were obtained after immunization with recombinant r595-207 LPS-OH, and clone S19-3 was obtained after immunization with recombinant r595-207 LPS-HF, both

VOL. 58, 1990

ANTIBODIES AGAINST CHLAMYDIAL LPS

207

TABLE 1. Reactivity of monoclonal antibodies with chlamydial and recombinant LPSs and with partial structures from them Hemolytic titer against SRBCs coated with:

Antibody

S10-3 S15-1 S15-2 S15-6 S19-3 S5-10 L21-6 E VI-Hl G III-C3 G II-B3 F VI-A4 F I-A6

S. minnesota r595-207

Isotype

IgM IgM IgM IgM IgM IgG3 IgG3 IgG2a IgG3 IgG2b IgG3 IgG2b

C. trachomatis

C. psittaci

LPS (150)"

LPS-OH (150)

LPS-HFr (50)

LPS (200)

(100)

LPS-OH (200)

LPS (200)

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