Analysis of the human serological response to proteins of Chlamydia trachomatis

Chlamydia-Specific IgA Secretion in the Female Reproductive Tract Induced via Per-Oral Immunization Confers Protection against Primary Chlamydia Challenge

Chlamydia trachomatis is an obligate intracellular pathogen that causes sexually transmitted disease. In women, chlamydial infections may cause pelvic inflammatory disease (PID), ectopic pregnancy, and infertility. The role of antibodies in protection against a primary Chlamydia infection is unclear and was a focus of this work. Using the C. muridarum mouse infection model, we show that intestinal mucosa is infected via intranasal (i.n.) or per-oral (p.o.) Chlamydia inoculation and that unlike the female reproductive tract (FRT) mucosa, it halts systemic Chlamydia dissemination. Moreover, p.o. immunization or infection with Chlamydia confers protection against per-vaginal (p.v.) challenge, resulting in significantly decreased bacterial burden in the FRT, accelerated Chlamydia clearance, and reduced hydrosalpinx pathology. In contrast, subcutaneous (s.c.) immunization conferred no protection against the p.v. challenge. Both p.o. and s.c. immunizations induced Chlamydia-specific serum IgA. However, IgA was found only in the vaginal washes and fecal extracts of p.o.-immunized animals. Following a p.v. challenge, unimmunized control and s.c.-s.c.-immunized animals developed Chlamydia-specific intestinal IgA yet failed to develop IgA in the FRT, indicating that IgA response in the FRT relies on the FRT to gastrointestinal tract (GIT) antigen transport. Vaginal secretions of p.o.-immunized animals neutralize Chlamydia in vivo, resulting in significantly lower Chlamydia burden in the FRT and Chlamydia transport to the GIT. We also show that infection of the GIT is not necessary for induction of protective immunity in the FRT, a finding that is important for the development of p.o. subunit vaccines to target Chlamydia and possibly other sexually transmitted pathogens.

Seroprevalence of antibodies against Pkn1, a novel potential immunogen, in Chlamydia trachomatis-infected Macaca nemestrina and human patients

Chlamydia trachomatis (CT) is an important cause of sexually transmitted genital tract infections (STIs) and trachoma. Despite major research into chlamydial pathogenesis and host immune responses, immunoprotection has been hampered by the incomplete understanding of protective immunity in the genital tract. Characterized vaccine candidates have shown variable efficacy ranging from no protection to partial protection in vivo. It is therefore a research priority to identify novel chlamydial antigens that may elicit protective immune responses against CT infection. In the present study we assessed the seroprevalence of antibodies against protein kinase1 (Pkn1), DNA ligaseA (LigA), and major outer membrane protein A (OmpA) following natural CT infection in humans and in experimentally induced CT infection in Macaca nemestrina. Antigenic stretches of Pkn1, LigA, and OmpA were identified using bioinformatic tools. Pkn1, LigA, and OmpA genes were cloned in bacterial expression vector and purified by affinity chromatography. Our results demonstrate significantly high seroprevalence of antibodies against purified Pkn1 and OmpA in sera obtained from the macaque animal model and human patients infected with CT. In contrast no significant seroreactivity was observed for LigA. The seroprevalence of antibodies against Pkn1 suggest that nonsurface chlamydial proteins could also be important for developing vaccines for C. trachomatis.

Impact of Chlamydia trachomatis in the reproductive setting: British Fertility Society Guidelines for practice

Chlamydia trachomatis infection of the genital tract is the most common sexually transmitted infection and has a world-wide distribution. The consequences of infection have an adverse effect on the reproductive health of women and are a common cause of infertility. Recent evidence also suggests an adverse effect on male reproduction. There is a need to standardise the approach in managing the impact of C. trachomatis infection on reproductive health. We have surveyed current UK practice towards screening and management of Chlamydia infections in the fertility setting. We found that at least 90% of clinicians surveyed offered screening. The literature on this topic was examined and revealed a paucity of solid evidence for estimating the risks of long-term reproductive sequelae following lower genital tract infection with C. trachomatis. The mechanism for the damage that occurs after Chlamydial infections is uncertain. However, instrumentation of the uterus in women with C. trachomatis infection is associated with a high risk of pelvic inflammatory disease, which can be prevented by appropriate antibiotic treatment and may prevent infected women from being at increased risk of the adverse sequelae, such as ectopic pregnancy and tubal factor infertility. Recommendations for practice have been proposed and the need for further studies is identified.

Deep sequencing-based discovery of the Chlamydia trachomatis transcriptome

Chlamydia trachomatis is an obligate intracellular pathogenic bacterium that has been refractory to genetic manipulations. Although the genomes of several strains have been sequenced, very little information is available on the gene structure of these bacteria. We used deep sequencing to define the transcriptome of purified elementary bodies (EB) and reticulate bodies (RB) of C. trachomatis L2b, respectively. Using an RNA-seq approach, we have mapped 363 transcriptional start sites (TSS) of annotated genes. Semi-quantitative analysis of mapped cDNA reads revealed differences in the RNA levels of 84 genes isolated from EB and RB, respectively. We have identified and in part confirmed 42 genome- and 1 plasmid-derived novel non-coding RNAs. The genome encoded non-coding RNA, ctrR0332 was one of the most abundantly and differentially expressed RNA in EB and RB, implying an important role in the developmental cycle of C. trachomatis. The detailed map of TSS in a thus far unprecedented resolution as a complement to the genome sequence will help to understand the organization, control and function of genes of this important pathogen.

Pgp3 antibody enzyme-linked immunosorbent assay, a sensitive and specific assay for seroepidemiological analysis of Chlamydia trachomatis infection

Understanding of the burden of Chlamydia trachomatis infection and its clinical sequelae is hampered by the absence of accurate, well-characterized tests using serological methods to determine past exposure to infection. An "in-house" immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) based on the C. trachomatis-specific antigen Pgp3 was produced and evaluated against three commercial ELISAs derived from the major outer membrane protein: the Medac pELISA plus, the Savyon SeroCT-IgG ELISA, and the Ani Labsystems IgG enzyme immunoassay. Sensitivities and specificities were determined using sera from both male and female patients (n = 356) for whom C. trachomatis had been detected in the lower genital tract at least 1 month prior to the testing of the sample and from 722 Chlamydia-negative children aged 2 to 13 years. The Pgp3 ELISA was significantly more sensitive (57.9% [95% confidence interval {95% CI}, 52.7 to 62.9%]) than the Ani Labsystems (49.2% [95% CI, 44.0 to 54.3%]; P = 0.003), SeroCT (47.2% [95% CI, 42.1 to 52.4%]; P < 0.0005), and Medac (44.4% [95% CI, 39.3 to 49.6%]; P < 0.0005) ELISAs. The Pgp3, Ani Labsystems, and SeroCT assays, but not the Medac assay, had significantly higher sensitivity for female specimens than for male specimens (73.8 versus 44.2%, 59.8 versus 40.5%, 55.5 versus 40%, and 45.7 versus 43.7%, respectively). For female patients, the Pgp3 assay was 14.0% (95% CI, 5.5 to 22.5%) more sensitive than the next most sensitive ELISA, the Ani Labsystems assay (P = 0.001). There was no significant difference in specificity between the Pgp3 (97.6% [95% CI, 96.2 to 98.6%]), Ani Labsystems (99% [95% CI, 97.7 to 99.6%]), SeroCT (97.2% [95% CI, 95.7 to 98.2%]), and Medac (96% [95% CI, 94.3 to 97.2%]) ELISAs. None of the ELISAs showed evidence of cross-reactivity with antibodies to Chlamydia pneumoniae.

Evaluation of an in silico predicted specific and immunogenic antigen from the OmcB protein for the serodiagnosis of Chlamydia trachomatis infections

Background

The OmcB protein is one of the most immunogenic proteins in C. trachomatis and C. pneumoniae infections. This protein is highly conserved leading to serum cross reactivity between the various chlamydial species. Since previous studies based on recombinant proteins failed to identify a species specific immune response against the OmcB protein, this study evaluated an in silico predicted specific and immunogenic antigen from the OmcB protein for the serodiagnosis of C. trachomatis infections.

Results

Using the ClustalW and Antigenic programs, we have selected two predicted specific and immunogenic regions in the OmcB protein: the N-terminal (Nt) region containing three epitopes and the C-terminal (Ct) region containing two epitopes with high scores. These regions were cloned into the PinPoint Xa-1 and pGEX-6P-1 expression vectors, incorporating a biotin purification tag and a glutathione-S-transferase tag, respectively. These regions were then expressed in E. coli. Only the pGEX-6P-1 has been found suitable for serological studies as its tag showed less cross reactivity with human sera and was retained for the evaluation of the selected antigens. Only the Ct region of the protein has been found to be well expressed in E. coli and was evaluated for its ability to be recognized by human sera. 384 sera were tested for the presence of IgG antibodies to C. trachomatis by our in house microimmunofluorescence (MIF) and the developed ELISA test. Using the MIF as the reference method, the developed OmcB Ct ELISA has a high specificity (94.3%) but a low sensitivity (23.9). Our results indicate that the use of the sequence alignment tool might be useful for identifying specific regions in an immunodominant antigen. However, the two epitopes, located in the selected Ct region, of the 24 predicted in the full length OmcB protein account for approximately 25% of the serological response detected by MIF, which limits the use of the developed ELISA test when screening C. trachomatis infections.

Conclusion

The developed ELISA test might be used as a confirmatory test to assess the specificity of serological results found by MIF.

[Chlamydia trachomatis antibody in Fitz-Hugh-Curtis syndrome]

BACKGROUND

Fitz-Hugh-Curtis (FHC) syndrome is inflammation of the liver capsule associated with pelvic inflammatory disease. We measured Chlamydia trachomatis antibodies in 30 female patients with acute abdominal pain for diagnosis of FHC-syndrome, and the results were compared with other tests.

METHODS

A dual-polymerase chain reaction was used for the detection of C. trachomatis in the cervix, and a micro-immunofluorescence test was performed to measure the antibody to C. trachomatis in serum. Cervical specimens were stained with Gram stain and cultured on chocolate agar for detection of Neisseria gonorrhoeae, and abdominal computed tomography (CT) and pelvic examinations were performed.

RESULTS

Of the 30 patients examined, 19 were diagnosed as having FHC-syndromes and 11 abdominal pains without FHC-syndrome. C. trachomatis was detected from one of the five patients studied, and no N. gonorrhoeae was isolated from the patients with FHC-syndrome. High titers of IgG antibody (1:512-1:1,024) to C. trachomatis were demonstrated in all patients with FHC-syndrome. The CT scan revealed perihepatitis in 14 patients with FHC-syndrome.

CONCLUSIONS

All patients with FHC-syndrome are associated with C. trachomatis infections, and a high titer of C. trachomatis antibody (IgG) is a very useful marker for FHC-syndrome.

Production and characterization of monoclonal antibodies to Chlamydia trachomatis

In order to develop an indigenous and reliable immunodiagnostic assay for Chlamydia trachomatis in India, monoclonal antibodies (MAbs) were developed. Serovar D of C. trachomatis (which was previously isolated from the genital tract of infected women) was propagated, purified, and used for production of monoclonal antibody. A total of 12 murine hybrid clones producing immunoglobulin G (IgG) class monoclonal antibodies to C. trachomatis (species-specific, B serogroup-specific, and serovar-specific) were developed. Enzyme-linked immunosorbent assay (ELISA) was used to screen developed murine MAbs with C. trachomatis antigen. Dot-ELISA was used to check the specificity of clones and was used for selecting hybridomas that produced anti-C. trachomatis MAb. There was no cross-reactivity of species-specific, B serogroup-specific, and D serovar-specific anti-major outer membrane protein (MOMP) monoclonal antibodies with other species of Chlamydiae i.e., C. pneumoniae and C. psitacci. Immunoblotting was done for further characterization of six of these clones, i.e., B2.2 and D5.1 (B serogroup-specific), D10.4 and G1.5 (species-specific), and H5.6 and E4.2 (D serovar-specific). Three of these clones D10.4 (species-specific), B2.2 (B serogroup-specific), and H5.6 (D serovar-specific) which reacted with 40 kd MOMP protein in Immunoblotting were used for further screening to detect C. trachomatis in endocervical specimens. The percent positivity with these clones for detection of C. trachomatis antigen by enzyme immunoassay (EIA) was 45% with D10.4, 43% with H5.6, and 35% with B2.2, while 46% of the specimens were found positive by cell culture method. This indicates a high prevalence of C. trachomatis infection in the female genital tract. The sensitivity and specificity of developed anti- MOMP monoclonal antibody in EIA for chlamydial antigen detection was 91.3% and 94.4% for D10.4 clone (species-specific), 91.30% and 98.1% for H5.6 (D serovar-specific) and 75.00% and 99.07% for B2.2 (B serogroup-specific) compared to cell culture method.

Evaluation of a recombinant enzyme-linked immunosorbent assay for detecting Chlamydophila psittaci antibodies in turkey sera

Chlamydophila psittaci (formerly Chlamydia psittaci) is one of the major pathogens associated with turkey respiratory disease. Devastating outbreaks with high mortality rates, similar to those of 1950 to 1970 in the USA occasionally occur, but respiratory signs without or with low mortality mostly characterize outbreaks now a day. Accurate diagnostic methods should be made available. The present study examined the sensitivity and specificity of a recombinant ELISA (rMOMP ELISA) for detecting Cp. psittaci major outer membrane specific antibodies in turkey sera. Test results were compared to those of immunoblotting and of a competitive ELISA (Chlamydia-psittaci-AK-EIA, Röhm Pharma, Germany) and an indirect ELISA (LPS/LGP) detecting antibodies to the lipopolysaccharide/lipoglycoprotein complex. The rMOMP ELISA was most sensitive as determined on serial dilutions of positive control sera originating from experimentally infected SPF turkeys. The competitive ELISA gave false positives since three negative controls reacted positive. For conventional sera, the sensitivities of the competitive ELISA, immunoblotting and the indirect ELISA were found to be 99.4, 93.1 and 82.2%, respectively, as compared to the rMOMP ELISA (100%). The specificities of the rMOMP ELISA, immunoblotting and the indirect ELISA were found to be 100% while the specificity of the competitive ELISA was only 2.7%. The rMOMP ELISA was chosen to compare the prevalence of chlamydiosis in 2002 with the one from 1992. In 2002, 188 on 200 (94%) turkey sera reacted positive compared to 175 on 200 (87.5%) in 1992 and like 10 years ago all examined farms were seropositive at slaughter. Interestingly, Belgian as well as French farms were seropositive.

Immunoreactivity and differential developmental expression of known and putative Chlamydia trachomatis membrane proteins for biologically variant serovars representing distinct disease groups

Chlamydia trachomatis is an intracellular bacterium that causes ocular and urogenital diseases worldwide. Membrane proteins have only been partially characterized, and the discovery of a nine-member polymorphic membrane protein gene family has enhanced interest in defining their function. We previously reported two putative insertion sequence-like elements in pmpC for biovariant Ba and one each for G and L2, suggesting horizontal gene transfer. Because of this and the tissue tropism differences for these biovariants, we analyzed by quantitative real-time RT-PCR pmpC expression relative to immunogenic protein genes ompA, groEL and gseA throughout development. Sera from infected adolescents were reacted by immunoblot against recombinant (r)PmpC and rMOMP. ompA and groEL revealed different developmental transcriptome profiles among the biovariants. pmpC expression occurred at 2 h, peaked at 18 for L2 (at 24 for Ba and G), with the highest mRNA levels throughout development for L2. pmpC expression as a function of time paralleled ompA expression with higher mRNA levels compared with groEL later in development. Only sera from D-, E- and G-infected patients reacted to rPmpC; all infected patients reacted to rMOMP. pmpC expression during logarithmic growth suggests a role in membrane building and/or integrity, which is supported by the presence of a signal peptidase and C-terminal phenylalanine in PmpC. Because phylogenetic analyses of pmpC segregate serovars according to tissue tropism, we speculate that biovariant transcriptome differences may contribute to this tropism. The heterogeneous biovariant pmpC expression throughout development and differential PmpC immunoreactivity also suggest a role for pmpC in antigenic variation.

Immune response to the Chlamydia trachomatis outer membrane protein PorB

The antigenicity of the outer membrane protein PorB during exposure to Chlamydia trachomatis was evaluated in humans and its immunogenicity was tested in mice. Although natural human infection resulted in strong serological responses to the major outer membrane protein (OmpA), antibodies to PorB were low or absent. Analogous to the responses observed in humans, mice inoculated with EB or challenged with EB produced weak anti-PorB antibody responses. PorB immunization of mice previously exposed to EB elicited strong PorB antibody responses. These findings support the fact that OmpA antibodies dominate the humoral immune response during natural infections and demonstrate that immunization with PorB overcomes the lack of immune response to PorB elicited during natural infection.

Identification of an in vivo CD4+ T cell-mediated response to polymorphic membrane proteins of Chlamydia pneumoniae during experimental infection

Chlamydia pneumoniae is an obligate intracellular bacterium that causes upper and lower respiratory tract infection in humans. C. pneumoniae harbors the polymorphic membrane protein (Pmp) family with 21 different proteins with a molecular mass around 100 kDa. The Pmps are species-specific, abundant and, together with major outer membrane protein and outer membrane protein 2, the dominant proteins in the C. pneumoniae outer membrane complex. Nevertheless, it is unknown whether Pmps are recognized by the cell-mediated immune response. To address this issue, C57BL/6J mice were infected intranasally with C. pneumoniae and the immune response to primary infection was investigated. We demonstrate, as expected, that the primary response is of the Th1 type by IgG2a- and IgG1-specific sELISA (Medac) on serum. In vivo-primed spleen lymphocytes were found to be reactive to Pmp8, Pmp20 and Pmp21 in an interferon-gamma ELISpot assay. The responses were shown to be mediated by CD4(+) T cells. To our knowledge, this is the first identification of antigens recognized by CD4(+) T cells during murine C. pneumoniae infection.

Polymorphic membrane protein H has evolved in parallel with the three disease-causing groups of Chlamydia trachomatis

Chlamydia trachomatis is a human pathogen causing trachoma, urogenital disease, and lymphogranuloma venereum (LGV). A family of nine polymorphic membrane protein genes (pmpA to pmpI), resembling autotransporter proteins, has recently been discovered in C. trachomatis. pmp genes are large and predicted to be outer membrane proteins. We hypothesized that they would contain useful nucleotide sequence variability for epidemiologic studies. Since sequence information is available only for serovars D and L2, we sought to determine the amount of diversity within an individual pmp gene among serovars. We used restriction fragment length polymorphism (RFLP) analysis as a primary screen to assess the amount of sequence divergence among the pmp genes for serovars A to L3 of C. trachomatis. RFLP analysis showed little variation for some of the genes, such as pmpA, but substantial variation in others, such as pmpI. pmpH and pmpE yielded RFLP patterns that clustered the 15 serovars into ocular, urogenital, and LGV groups, and both proteins have been localized to the outer membrane. Therefore, we chose to sequence pmpE, pmpH, and pmpI from each of the 15 serovars. Evolutionary analysis showed three distinct divergence patterns. PmpI was least variable, resulting in an ambiguous evolutionary pattern. PmpE showed a high degree of diversity in the ocular strains compared to the other strains. Finally, the evolution of PmpH shows three groups that reflect disease groups, suggesting this protein may play a role in pathogenesis.

Characterization of the humoral immune response to Chlamydia outer membrane protein 2 in chlamydial infection

Detection of antibodies to an outer membrane protein 2 (OMP2) by enzyme-linked immunosorbent assay (ELISA) by using either the Chlamydia trachomatis- or the Chlamydia pneumoniae-specific protein was investigated. OMP2 is an immunodominant antigen giving rise to antibody responses in humans infected with different C. trachomatis serovars (A to C and D to K) or with C. pneumoniae, which could be detected by OMP2 ELISA. OMP2 ELISA is not species specific, but antibody titers were usually higher on the homologous protein. The sensitivity of this assay was high but varied according to the "gold standard" applied. Levels of antibody to C. pneumoniae OMP2 as detected by ELISA seem to return to background or near-background values within a shorter period of time compared to antibodies to C. pneumoniae detected by microimmunofluorescence (MIF), making it more likely that positive results in ELISA reflect recent infection. Thus, OMP2 ELISA has distinct advantages over MIF and commercially available ELISAs and might be a useful tool for the serodiagnosis of chlamydial infection.

Detection of Chlamydia pneumoniae antigenin PBMNCs of healthy blood donors

BACKGROUND

Because it has been increasingly recognized that Chlamydia pneumoniae may be linked to some chronic inflammatory diseases, including atherosclerosis, detection of this pathogen in blood from patients may be valuable in the diagnosis of such diseases. However, the prevalence of chlamydia in the blood of healthy donors has not yet been extensively studied.

STUDY DESIGN AND METHODS

The presence of C. pneumoniae in PBMNCs obtained from healthy persons who donated blood for blood transfusion was assessed by a PCR that was specific for the C. pneumoniae 16S rRNA gene and by the use of staining with FITC-conjugated chlamydia MoAb.

RESULTS

Twenty-one (8.9%) of 237 blood samples tested showed the presence of C. pneumoniae DNA and antigen in the PBMNCs. There was no significant difference in the presence of chlamydia in blood according to sex or to age between 20 and 59 years of age. However, a possible seasonal variation in the presence of chlamydia in blood from healthy donors was suggested by the results obtained.

CONCLUSION

A significant percentage of healthy donors carry C. pneumoniae, which may be a risk factor for some chronic diseases.

Use of a reverse dot blot procedure to identify the presence of multiple serovars in Chlamydia trachomatis urogenital infection

Epidemiologic research requires identification of Chlamydia trachomatis serovars and detection of mixed infection. Antibody-based serotyping is unworkable when specimens are urine or vaginal swabs. We developed a reverse dot blot (RDB) to screen for multiple serotypes in these specimens. RDB yielded the predicted results on all artificially mixed samples and on seven of eight clinically mixed samples.

PCR-based method for isolation and detection of Chlamydia pneumoniae DNA in cerebrospinal fluids

Since current studies indicate the possible involvement of Chlamydia pneumoniae in the pathogenesis of multiple sclerosis (MS), demonstration of C. pneumoniae in the cerebrospinal fluid (CSF) of patients with MS is highly desirable. However, there is controversy concerning the detection of C. pneumoniae in CSFs from MS patients due to the lack of a standard protocol for extraction and detection of C. pneumoniae DNA. In this regard, we attempted to establish a highly effective extraction protocol for C. pneumoniae DNA from CSFs utilizing a commercial kit and a PCR detection method. The extraction and PCR detection protocol established in this study succeeded in detecting as few as 20 C. pneumoniae organisms in 200 microl of mock CSF. The use of this protocol to detect C. pneumoniae DNA in CSFs revealed that 68% of CSF samples obtained from patients with MS were positive (11 out of 16 samples) for chlamydia DNA. Thus, the protocol established here is sensitive enough to detect chlamydia DNA from CSFs and can be used by other laboratories for evaluation of the presence of chlamydiae in CSFs because the protocol is based on the use of a commercial kit.

Identification of polymorphic outer membrane proteins of Chlamydia psittaci 6BC

The genomes of Chlamydia spp. encode a family of putative outer membrane proteins, referred to as polymorphic outer membrane proteins (POMPs), which may play a role in the avoidance of host immune defenses. We analyzed avian strain 6BC of Chlamydia psittaci by polyacrylamide gel electrophoresis for the expression of POMPs. At least six putative POMPs were identified on the basis of their size (90 to 110 kDa) and labeling with an outer membrane-specific probe, 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine. Three of the putative POMPs reacted with antiserum raised against a recombinant ovine C. psittaci strain POMP, and two possessed surface-exposed, trypsin-sensitive sites. The POMPs were dependent on disulfide bonds for their maintenance in sodium lauryl sarcosine- and sodium dodecyl sulfate-insoluble complexes but did not appear to be interpeptide disulfide bond cross-linked. The putative POMPs were found to be synthesized during the late phase of the chlamydial developmental cycle, cotemporally with the cysteine-rich doublet periplasmic proteins.

Characterization of outer membrane proteins in Chlamydia trachomatis LGV serovar L2

We used a photoactivatable, lipophilic reagent, 3'-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine, to label proteins in the outer membrane of elementary bodies of Chlamydia trachomatis LGV serovar L2 and mass spectrometry to identify the labeled proteins. The identified proteins were polymorphic outer membrane proteins E, G, and H, which were made late in the developmental cycle, the major outer membrane protein, and a mixture of 46-kDa proteins consisting of the open reading frame 623 protein and possibly a modified form of the major outer membrane protein.

The use of serologic tests for the diagnosis of chlamydial infections

Serology is commonly used for the diagnosis of acute Chlamydia pneumoniae infections and also for the diagnosis of complicated Chlamydia trachomatis infections. Furthermore, recent sero-epidemiological studies have linked C. pneumoniae infection with several diseases traditionally considered non-infectious. The objectives of this mini-review are to critically review and discuss some selected analytical and methodological aspects, controversies and current problems in chlamydial serodiagnosis. To illustrate our views we present some original data of the comparison of current technologies. The review of the literature revealed high variability in methodologies applied to different studies. This observation was supported by our own data, which explains occasional conflicting clinical interpretation. Although the microimmunofluorescence (MIF) technique is generally considered as the gold standard for serodiagnosis of chlamydial infections, assay conditions are highly variable and hence pose a major problem in the interpretation of the results. For instance, many recent studies linking C. pneumoniae and atherosclerosis have utilized MIF techniques with variable threshold criteria for the positivity, in combination with selection bias of cases and controls possibly leading to conflicting results. Variability of assay conditions is also a common problem with Western blots, and interpretation is problematic when both anti-C. pneumoniae and anti-C. trachomatis antibodies are present. Furthermore, there is a lot of disagreement in serological criteria applied to recently emerged enzyme immunoassay (EIA) techniques when these assays are used for acute and non-acute clinical conditions and their association with Chlamydiae. In conclusion, standardization of serological techniques and the development of uniform criteria for interpretation of serologic findings is necessary to increase our knowledge of the biology of Chlamydiae, pathogenesis of any chlamydial infection and chronic infections in particular.

Analysis of the humoral immune response to Chlamydia pneumoniae by immunoblotting and immunoprecipitation

Chlamydia pneumoniae is a widely spread agent of respiratory tract infections in humans. A reliable serodiagnosis of the disease is hampered by the poor knowledge about immunodominant antigens in C. pneumoniae infections. We applied a novel strategy to identify immunogenic proteins of C. pneumoniae TW183 combining metabolic radiolabeling of de novo-synthesized chlamydial antigens with immunoprecipitation. By this technique C. pneumoniae antigens of approximately 160, 97 to 99, 60 to 62, 40, 27, and 15 kDa were detected in the vast majority of sera from patients with a current C. pneumoniae infection. By immunoblotting purified elementary bodies of C. pneumoniae TW183 with the same sera, only the 60- to 62-kDa antigen could be detected consistently. Sequential immunoprecipitation performed at different stages of the chlamydial developmental cycle revealed that the 60- to 62-kDa antigen is strongly upregulated after 24 to 48 h of host cell infection and is presented as a major immunogen in both C. pneumoniae-infected patients and mice. We conclude that, due to its high sensitivity and concurrent preservation of conformational epitopes, metabolic radiolabeling of chlamydial antigens combined with immunoprecipitation may be a useful method to reveal important immunogens in respiratory C. pneumoniae infection which might have been missed by immunoblot analysis.

Characterization and intracellular trafficking pattern of vacuoles containing Chlamydia pneumoniae in human epithelial cells

Chlamydiae are obligate intracellular pathogens that reside within a membrane-bound vacuole throughout their developmental cycle. In this study, the intraphagosomal pH of Chlamydia pneumoniae (Cpn) was qualitatively assessed, and the intracellular fate of the pathogen-containing vacuole and its interaction with endocytic organelles in human epithelial cells were analysed using conventional immunofluorescence and confocal microscopy. The pH-sensitive probes acridine orange (AO), LysoTracker (LyT) and DAMP did not accumulate in the bacterial inclusion. In addition, exposure of cells to bafilomycin A1(BafA1), a potent acidification inhibitor, did not inhibit or delay chlamydial growth. The chlamydial compartment was not accessible to the fluid-phase tracer Texas Red (TR)-dextran and did not exhibit any level of staining for the late endosomal marker cation-independent mannose-6-phosphate receptor (Ci-M6PR) or for the lysosomal-associated membrane proteins (LAMP-1 and -2) and CD63. In addition, transferrin receptor (TfR)-enriched vesicles were observed close to Cpn vacuoles, potentially indicating a specific translocation of these organelles through the cytoplasm to the vicinity of the vacuole. We conclude that Cpn, like other chlamydial spp., circumvents the host endocytic pathway and inhabits a non-acidic vacuole, which is dissociated from late endosomes and lysosomes, but selectively accumulates early endosomes.

Different humoral immune response to Chlamydia trachomatis major outer membrane protein variable domains I and IV in Chlamydia-infected patients with or without reactive arthritis

OBJECTIVE

The possibility that some bacterial-specific factor(s) may play a role in triggering Chlamydia trachomatis reactive arthritis was investigated.

METHODS

Since the variable domains of the major outer membrane protein (MOMP) contain the serovar-determining epitopes of C. trachomatis, the ability of serum IgG to recognize peptides mimicking these epitopes was determined in 2 groups of infected patients, one with and the other without reactive arthritis. Because asymptomatic C. trachomatis infections are frequent, and nonspecific reactions due to inflammation could be observed, this study was also performed with samples from healthy blood donors and from patients with inflammatory arthritis unrelated to C. trachomatis infection.

RESULTS

A predominant reactivity against peptides duplicating the J serovar-specific epitopes was only observed in the group of patients with reactive arthritis. For positive samples, differences between the two groups of C. trachomatis-infected patients were clearly observed. The mean numbers of positive responses obtained for each of the 7 peptides of the MOMP domain I or each of the 8 peptides of the MOMP domain IV were significantly higher for samples from patients with reactive arthritis (4.7 and 6) than for those from patients with only C. trachomatis urogenital infection (1.3 and 2.9).

CONCLUSION

Patients with reactive arthritis had a pattern of reactivities that was compatible with infection by several serotypes of bacteria. Repeated exposures to C. trachomatis might therefore be involved in the development of the disease.

Oxidative activity of turkey monocytes, following the inoculation with Chlamydia psittaci

Chemiluminescence (CL) was used to investigate the competence of turkey monocytes to mount a respiratory burst response upon interaction with Chlamydia psittaci. The oxidative activity of purified turkey monocytes, following inoculation with the avian C. psittaci serovar D strain 92/1293, was studied using luminol- and lucigenin-enhanced CL. Purified turkey monocytes were inoculated with C. psittaci at multiplicity of infection (MOI) of approximately 100, 10 and 1. In the presence of luminol, no detectable CL or only a weak CL response was obtained, and if present it increased with increasing MOI. Either sham inoculated monocytes, or monocyte-free control assays supplemented with C. psittaci, gave no detectable luminol-enhanced CL responses. In the lucigenin-enhanced assays, monocytes inoculated with C. psittaci demonstrated an immediate CL peak, the height of which was proportional to the MOI used. Following inoculations at a MOI 1, a faint second peak was observed, when applying high concentrations of lucigenin. Sham inoculated monocytes gave no detectable lucigenin-enhanced CL responses. However, in the presence of lucigenin, the addition of C psittaci to monocyte-free controls also resulted in an immediate CL peak, though no second peak was detected. This immediate lucigenin-dependent CL peak induced by C. psittaci was similar to the one observed in the presence of monocytes, and was not inhibited by superoxide dismutase. We demonstrated that this avian C. psittaci strain induces only a very weak respiratory burst response in turkey monocytes. In contrast, C. psittaci itself elicited an intense non-superoxide mediated lucigenin-dependent CL, indicating that in chlamydial research the detection of superoxide, using lucigenin, should be confirmed with a specific superoxide inhibitor.

Identification of two novel genes encoding 97- to 99-kilodalton outer membrane proteins of Chlamydia pneumoniae

Two genes encoding 97- to 99-kDa Chlamydia pneumoniae VR1310 outer membrane proteins (Omp4 and Omp5) with mutual similarity were cloned and sequenced. The proteins were shown to be constituents of the C. pneumoniae outer membrane complex, and the deduced amino acid sequences were similar to those of putative outer membrane proteins encoded by the Chlamydia psittaci and Chlamydia trachomatis gene families. By use of a monospecific polyclonal antibody against purified recombinant Omp4, it was shown that without heating, the protein migrated at 65 to 75 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Immunoelectron microscopy showed that epitopes of Omp4 were exposed on the surface of C. pneumoniae elementary bodies, reticulate bodies, and outer membrane complex. Proteins encoded by the C. pneumoniae gene family seem to be dominant antigens in experimentally infected mice.

Prevalence of specific antibodies to Chlamydia pneumoniae in Korea

To clarify the endemic status of Chlamydia pneumoniae in Korea, the incidence of antibodies in 564 serum samples from healthy individuals, patients with respiratory infection, and cord blood specimens was evaluated. We conclude that C. pneumoniae infection is highly endemic in Korea and that this infection is associated with acute respiratory diseases.

Immunoelectron microscopic localisation of the OMP90 family on the outer membrane surface of Chlamydia psittaci

The putative outer membrane location of the OMP90 (formerly POMP) family from the ovine abortion strain of Chlamydia psittaci was investigated by immunoelectron microscopy. Using a non-embedding technique, antigens were shown to be localised on the outer membrane surface of both elementary and reticulate bodies, the infectious and non-infectious forms of Chlamydiae respectively. Antibodies affinity-purified against the expressed amino- and carboxy-terminal halves of one of the family members. OMP90A, demonstrated that the amino half is surface-exposed while the carboxyl half is most probably localised internally. Surface localisation on elementary bodies indicates the importance of these proteins as protective antigen candidates.

Analysis of the humoral immune response to Chlamydia outer membrane protein 2

The humoral immune response to Chlamydia outer membrane protein 2 (Omp2) was studied. Omp2 is a highly genus-conserved structural protein of all Chlamydia species, containing a variable N-terminal fragment. To analyze where the immunogenic parts were localized, seven highly purified truncated fusion proteins constituting different regions of the protein were produced (Chlamydia pneumoniae-Omp2aa23-aa93, Chlamydia psittaci-Omp2aa23-aa94, and Chlamydia trachomatis-Omp2aa23-aa84, aa87-aa547, aa23-aa182, aa167-aa434, aa420-aa547). By an enzyme-linked immunosorbent assay with serologically defined patient sera, Omp2 was found to be a major immunogen of both C. pneumoniae and C. trachomatis infections (P < 0.0001). The humoral immune responses were not confined to any particular region of the Omp2 protein, and no species-specific anti-Omp2 immunoglobulins were detected.

Use of DNA purification kits for polymerase chain reaction testing of Gen-Probe Chlamydia trachomatis PACE 2 specimens

BACKGROUND AND OBJECTIVES

Confirmation testing using nucleic acid amplification has been shown to improve the sensitivity and specificity of screening tests for Chlamydia trachomatis. However, no critical information on the use of these techniques as an adjunct to Gen-Probe hybridization testing, one of the most common screening methods, has been reported to date. We examined the Roche AMPLICOR PCR C. trachomatis Test (Roche Diagnostic Systems, Branchburg, NJ) as a confirmatory test for the Gen-Probe PACE 2 C. trachomatis Test (San Diego, CA). Further, to mitigate the possible effect of interfering compounds in the Gen-Probe PACE 2 transport medium, we tested various DNA purification techniques.

STUDY DESIGN

C. trachomatis elementary bodies were used to spike PACE 2 Transport medium, which was serially diluted, then tested by polymerase chain reaction (PCR). Six parallel dilution series were conducted: (1) saline dilutions tested by the Syva Direct Specimen Test, (2) Roche AMPLICOR transport medium dilutions tested by PCR, and (3-6) dilutions in PACE 2 transport medium purified respectively by GENECLEAN II (BIO101, Vista, CA), Puregene (Gentra Systems, Inc., Research Triangle Park, NC), Microcon 100 (Amicon, Inc., Beverly, MA) DNA isolation kits, and no DNA purification, all tested by PCR. The system giving the best results by in vitro endpoint dilution trials was then used to confirm human specimens previously tested by the Gen-Probe method.

RESULTS

PCR detected C. trachomatis at 11 twofold dilutions greater than PACE 2 and equivalent to detection of single elementary body by Syva Direct Specimen Test. DNA purification of spiked PACE 2 transport medium by the Microcon 100 kit produced the most consistent PCR detection endpoints, equivalent to endpoints of spiked AMPLICOR transport medium. Endpoints with no DNA purification step were variable and lower. Of 78 endocervical specimens negative by PACE 2 and Gen-Probe Probe Competition Assay, 12 (15.3%) were positive by Microcon DNA purification/PCR testing.

CONCLUSIONS

PCR can be used as confirmation method for Gen-Probe PACE 2 testing, but testing must be performed with a DNA purification procedure.

Differences in the association of Chlamydia trachomatis serovar E and serovar L2 with epithelial cells in vitro may reflect biological differences in vivo

Chlamydia trachomatis serovar E is one of the most common bacterial sexually transmitted pathogens. Since it is an obligate intracellular bacterium, efficient colonization of genital mucosal epithelial cells is crucial to the infectious process. Serovar E elementary bodies (EB) metabolically radiolabeled with 35S-Cys-Met and harvested from microcarrier bead cultures, which significantly improves the infectious EB-to-particle ratio, provided a more accurate picture of the parameters of attachment of EB to human endometrial epithelial cells (HEC-1B) than did less infectious 14C-EB harvested from flask cultures. Binding of serovar E EB was (i) equivalent at 35 and 4 degrees C, (ii) decreased by preexposure of EB to heat or the topical microbicide C31G, (iii) comparable among common eukaryotic cell lines (HeLa, McCoy), and (iv) significantly increased to the apical surfaces of polarized cells versus nonpolarized cells. In parallel experiments with C. trachomatis serovar L2, serovar E attachment was not affected by heparin or heparan sulfate whereas these glucosaminoglycans dramatically reduced serovar L2 attachment. These data were confirmed by competitive inhibition of serovar E binding and infectivity by excess unlabeled live and UV-inactivated serovar E EB but not by excess serovar L2 EB. The noninvasive serovar E strains in the lumen of the genital tract enter and exit the apical domains of target columnar epithelial cells to spread canalicularly in an ascending fashion from the lower to the upper genital tract. In contrast, the invasive serovar L2 strains are primarily submucosal pathogens and likely use the glucosaminoglycans concentrated in the extracellular matrix to colonize the basolateral domains of mucosal epithelia to perpetuate the infectious process.

The presence of serum antibody to the chlamydial heat shock protein (CHSP60) as a diagnostic test for tubal factor infertility

OBJECTIVE

To study the utility of testing for heat shock protein 60 (CHSP60) antibodies in the diagnosis of tubal factor infertility.

DESIGN

Prospective case control.

SETTING

Canadian university hospital infertility clinic.

PATIENT(S)

Women presenting for infertility investigation.

INTERVENTION(S)

Sera were collected from 77 patients.

MAIN OUTCOME MEASURE(S)

The relationship between tubal factor infertility and the presence of antibodies to Chlamydia trachomatis and CHSP60 was assessed.

RESULT(S)

There were no significant differences between antibodies to C. trachomatis in women with tubal factor infertility (63%) and other causes of infertility (46%). However, more women with tubal factor infertility (44%) had anti-CHSP60 antibodies compared with other causes of infertility (8%). Antibody testing for C. trachomatis has only a 63% sensitivity and a 54% specificity for detecting tubal factor infertility. In contrast, the CHSP60 antibody test has a 44% sensitivity and a 92% specificity for detecting tubal factor infertility. There is a good positive likelihood ratio of 5.5 for CHSP60 antibody testing detecting the presence of tubal factor infertility. Combining CHSP60 antibody with antibody testing for C. trachomatis has an excellent positive likelihood ratio of 10 for the detection of C. trachomatis-associated tubal factor infertility.

CONCLUSION(S)

CHSP60 antibody testing is a more accurate test than antibody testing for C. trachomatis for predicting chlamydia-associated tubal factor infertility. These tests, when used in combination at initial infertility evaluation, would provide a rapid noninterventive means of diagnosing tubal factor infertility.

Antigenic and molecular analyses of different Chlamydia pneumoniae strains

Chlamydia pneumoniae is an important human respiratory pathogen. Classification of C. pneumoniae isolates into distinguishable serovars or genotypes has not yet been reported. To determine whether antigenic or molecular variants among C. pneumoniae isolates exist, six strains were studied via immunoblot analysis and DNA sequence determination of the entire major outer membrane protein (MOMP) gene omp1. The strains included four prototype strains and two clinical isolates from our laboratory. Immunoblot analysis of sera from patients infected with C. pneumoniae revealed antigenic differences between the C. pneumoniae strains. Strong reactivity of one serum sample with a 65-kDa protein in two C. pneumoniae strains which was not observed with the other strains was the most prominent finding. All sera reacted with the 40-kDa MOMP. Comparison of the omp1 DNA sequences revealed that the omp1 genes of all strains were identical and were 100% identical to the sequence of the omp1 gene of C. pneumoniae AR-39. The results of this study demonstrate that unlike C. trachomatis, the omp1 gene is conserved in C. pneumoniae. Furthermore, it was shown that C. pneumoniae strains are antigenically different. This finding indicates that more than one serovar of C. pneumoniae exist.

Oral immunization with an anti-idiotypic antibody to the exoglycolipid antigen protects against experimental Chlamydia trachomatis infection

Chlamydia trachomatis is the leading cause worldwide of preventable infectious blindness (trachoma) and sexually transmitted disease, including nongonoccocal urethritis and pelvic inflammatory disease. To date, no effective vaccine against C. trachomatis infection has been identified. A monoclonal anti-idiotypic antibody (anti-Id) to the chlamydial exoglycolipid antigen (GLXA) was tested in a murine model of ocular chlamydial infection for its ability to induce systemic immunity, which reduces microbiologic and clinical disease. The anti-Id to GLXA, delivered either systemically in soluble form or orally after encapsulation in poly(lactide) microspheres, induced significant protective immunity against ocular challenge of mice with a human biovar of C. trachomatis. Protection was associated with induction of anti-GLXA antibody and anti-chlamydial neutralizing antibody.

Species-, serogroup-, and serovar-specific epitopes are juxtaposed in variable sequence region 4 of the major outer membrane proteins of some Chlamydia trachomatis serovars

Synthetic peptides and murine monoclonal antibodies were used to map cross-reactive chlamydial epitopes. A species-specific epitope in the central region of variable sequence region 4 abuts the amino-terminal end of a B-serogroup-specific or F/G-serogroup-specific epitope, which in turn abuts known serovar-specific epitopes. The carboxyl-terminal portion of variable sequence region 4 (residues 297 to 314) comprises a region of end-to-end B-cell epitopes in some serovars of the B and F/G serogroups.

Development of a simplified polymerase chain reaction-enzyme immunoassay for the detection of Chlamydia pneumoniae

The 16S rRNA genes of two Chlamydia pneumoniae and two C. psittaci strains of different serovars were sequenced then compared to previously reported Chlamydia 16S rRNA gene sequences. Chlamydia pneumoniae-specific regions were identified and specific primers for nested PCR were synthesized. Nested PCR reactions were performed, in a single tube, by varying the annealing temperature of the amplification cycles. The initial thermal cycles were selected to allow annealing and extension of only the outer primer pair, whilst in later cycles a temperature that allowed inner primer annealing was employed. The inner primers were labelled, one with biotin and the other with fluorescein and consequently the dual labelled amplicon could be immobilized onto antibiotin-coated microtitre plates and detected colorimetrically via an antifluorescein-enzyme conjugate. The assay was found to be sensitive and specific. No cross reactions were observed with C. trachomatis, C. psittaci or other common respiratory pathogens.

Characterization of two conformational epitopes of the Chlamydia trachomatis serovar L2 DnaK immunogen

Chlamydia trachomatis DnaK is an important immunogen in chlamydial infections. DnaK is composed of a conserved N-terminal ATP-binding domain and a variable C-terminal peptide-binding domain. To locate the immunogenic part of C. trachomatis Dnak, we generated monoclonal antibodies (MAbs) against this protein. By use of recombinant DNA techniques, we located the epitopes for two MAbs in the C-terminal variable part. Although the antibodies reacted in an immunoblot assay, it was not possible to map the epitopes completely by use of 16-mer synthetic peptides displaced by one amino acid corresponding to the C-terminal part of C. trachomatis DnaK. To determine the limits of the epitopes, C. trachomatis DnaK and glutatione S-transferase fusion proteins were constructed and affinity purified. The purified DnaK fusion proteins were used for a fluid-phase inhibition enzyme-linked immunosorbent assay with the two antibodies. The epitopes were found not to overlap. To obtain DnaK fragments recognized by the antibodies with the same affinity as native C. trachomatis DnaK, it was necessary to express, respectively, regions of 127 and 77 amino acids. The MAbs described in this study thus recognized conformational epitopes of C. trachomatis DnaK.

Immune Protection Against Chlamydia trachomatis in Females

Despite significant advances in our understanding of the biology and antigenic structure of Chlamydia trachomatis, and the epidemiology and clinical spectrum of chlamydial disease, the magnitude of morbidity from human chlamydial infections remains an important public health concern. Control of chlamydial disease will likely depend on a multidisciplinary approach, including the development of immunoprophylactic or immunotherapeutic strategies. Reasonable progress has been made in understanding specific immune mechanisms that contribute to host immunity in experimental models of chlamydial infection. However, studies of human immunity have not been so successful. This is particularly evident in that studies to address the development and role of mucosal immune responses to urogenital chlamydial infections have not been forthcoming. The following review is a brief summary of our current knowledge of protective immunity to chlamydial urogenital infections of females. It is not meant to be exhaustive, but instead to touch upon aspects of protective immunity that have been described in both human and experimental animal models of chlamydial infection.

Serologic evidence of Chlamydia trachomatis infection and risk of preterm birth

OBJECTIVE

To determine whether serologic evidence of Chlamydia trachomatis during pregnancy is a risk factor for preterm delivery (before 37 weeks' gestation).

DESIGN

Chart review.

SETTING

Antenatal clinics associated with a teaching hospital.

PATIENTS

A group of 103 unselected consecutive patients presenting for routine prenatal care.

OUTCOME MEASURES

Pregnancy outcome and C. trachomatis serologic status.

RESULTS

A total of 21 women (20%) were found to be seropositive for IgG antibodies to C. trachomatis. They were similar to the seronegative women with respect to maternal age, parity, history of preterm birth, obstetric or medical problems, smoking status, history of drug abuse, educational status and psychosocial stressors. The seropositive women were significantly more likely than the seronegative women to have a preterm birth (24% [5/21] v. 7% [6/82]i p = 0.029, odds ratio 3.96, 95% confidence interval 1.08 to 14.57), an infant with a lower mean gestational age at birth (262 [standard deviation (SD) 19] days v. 273 [SD 15] days; p = 0.0052) and an infant with a lower mean birth weight (3125 [SD 692] g v. 3473 [SD 696] g; p = 0.0434). The positive predictive value of a seropositive result for preterm birth was 31% (5/16); the negative predictive value of a seronegative result for preterm birth was 8% (6/76).

CONCLUSION

Women with serologic evidence of C. trachomatis may be at risk for preterm birth. Further study is required to determine whether serologic testing for C. trachomatis should be a routine part of prenatal care.

Deviation of immune response to Chlamydia psittaci outer membrane protein in lipopolysaccharide-hyporesponsive mice

The outcome of infection is determined by both the quantity and the quality of an induced immune response. In particular, it has been demonstrated for selected pathogens that induction of TH1 or TH2 type helper T-cell subsets determines whether an immune response gives rise to protective immunity or disease-associated immunopathology. The nature of the antigen and the type of antigen-presenting cells recruited in the induction of a response are critical factors that influence the quality of the immune response. Of particular interest in this respect is the immune response to bacterial particles and the impact of cell wall-associated lipopolysaccharide (LPS) on that response. Nonspecific activation of macrophages and B lymphocytes by LPS could skew the phenotype of activated antigen-presenting cells and selectively alter the immunoglobulin isotypes and helper T-cell subsets that are induced following infection. In an initial attempt to detect immune deviation associated with LPS stimulation, we have compared the immunoglobulin isotypes of antibodies specific for the cysteine-rich outer membrane protein Omp2 induced in normal and LPS-hyporesponsive mice following immunization with Chlamydia psittaci strain guinea pig inclusion conjunctivitis whole elementary bodies. We report that there is a dramatic shift of Omp2-specific antibody from predominantly immunoglobulin G2a (IgG2a) isotype in LPS-hyporesponsive mice to high levels of IgG1 isotype in LPS-responder strains. The dependence of the IgG1 isotype shift on the LPS responder status is linked to the structure of the antigen and its natural processing pathway since LPS-hyporesponsive mice are not, in general, deficient in IgG1 antibody production. In particular, the antibody response to purified recombinant Omp2 is predominantly of the IgG1 isotype even in LPS-hyporesponsive mice.

Dissociation of immune determinants of outer membrane proteins of Chlamydia psittaci strain guinea pig inclusion conjunctivitis

Chlamydia trachomatis is an important human pathogen. Research to develop a Chlamydia vaccine has focused on the major outer membrane protein (MOMP). Determinants of this protein elicit serovar-specific neutralizing antibodies which are thought to play a critical role in protective immunity. MOMP-specific antibody responses are highly variable in the polymorphic population. Genetic factors which might influence the MOMP-specific immune response are consequently of particular interest. The C. psittaci strain guinea pig inclusion conjunctivitis (GPIC) is a natural pathogen of the guinea pig that causes both ocular and genital tract infections that closely resemble those caused by C. trachomatis in humans. As such, it provides an excellent model for disease. In this report, we explore the influence of major histocompatibility complex-linked genes on the MOMP-specific antibody response in mice immunized with either whole GPIC elementary bodies or recombinant GPIC MOMP. Our results indicate that the MOMP-specific antibody response is major histocompatibility complex linked such that mice of the H-2d haplotype are high responders while mice of the H-2k haplotype are low responders. We demonstrate that MOMP-specific B cells are present in H-2k strains which are, however, deficient in MOMP-specific helper T cells. Although immunization of low-MOMP-responder strains with whole chlamydial elementary bodies induces high levels of immunoglobulin G antibody specific for Omp2, the cysteine-rich outer membrane protein, MOMP-specific B cells are unable to receive help from Omp2-specific T cells. The failure of intermolecular help from Omp2-specific T cells and related observations raise important issues regarding the processing and presentation of chlamydial antigens and the design of optimal subunit vaccines.

Trachoma and LGV biovars of Chlamydia trachomatis share the same glycosaminoglycan-dependent mechanism for infection of eukaryotic cells

A sulphated glycosaminoglycan-dependent mechanism of microbial infection for mammalian cells was characterized for the Chlamydia trachomatis trachoma and lymphogranuloma venereum (LGV) biovars. We demonstrated that the trachoma and LGV biovars compete for the same receptor(s) on host cells and that their infectivity was inhibited by heparin or heparan sulphate. Using a specific heparan sulphate lyase (heparitinase) to treat organisms, the infectivity of both biovars was abolished. Furthermore, exogenous heparan sulphate rescued chlamydial infectivity following treatment with heparitinase and the restored infectivity was neutralized by an anti-heparan sulphate monoclonal antibody. These data suggest that heparan sulphate-like-mediated interactions between C. trachomatis and eukaryotic cells are essential for infectivity.

Neutralization of Chlamydia psittaci with monoclonal antibodies

Neutralization of Chlamydia (C.) psittaci avian strain P-1041 was examined in vitro using monoclonal antibodies (MAbs). Of the 10 MAbs used, 6 were found to exhibit neutralizing capability. These include 3 against major outer membrane protein (MOMP), 1 against lipopolysaccharide (LPS) and 2 against other protein molecules [90 kilodalton (kDa) and 90/50 kDa]. Most neutralizing MAbs were dependent on complement for efficient neutralization, while a strain-specific MAb (2B5) against the 90 kDa protein displayed a different requirement for complement and neutralized the infectivity of the P-1041 at high concentrations without complement. By competitive inhibition enzyme-linked immunosorbent assay (competitive inhibition ELISA), all 3 neutralizing anti-MOMP MAbs were demonstrated to recognize different epitopes found in very close proximity to each other on the outer membrane.

Identification of T-cell stimulatory antigens of Chlamydia trachomatis using synovial fluid-derived T-cell clones

Chlamydia trachomatis is a major cause of sexually transmitted disease, infertility and reactive arthritis in the Western world, and of trachoma in the developing world. There is evidence that the chronic inflammatory reaction seen in diseases associated with chlamydiae represents a delayed-type hypersensitivity response to chlamydial antigens. Little is known about which chlamydial antigens elicit T-cell responses yet such information could have important implications in terms of both immunopathological understanding of these diseases and immunoprophylaxis design. In this study, 61 chlamydia-specific T-cell clones have been produced from the synovial fluid of an individual with sexually acquired reactive arthritis (SARA). Ten clones have been characterized in detail and used to identify T-cell stimulatory antigens of chlamydiae by means of T-cell immunoblotting. Two distinct antigenic fractions have been identified, one recognized by three of the clones (molecular weight 18,000), the other recognized by six of the clones (molecular weight 30,000). The fractions are distinct from the major outer membrane protein, the 57,000 MW stress protein and the 60,000 MW cysteine-rich membrane protein of chlamydiae. The major histocompatibility complex (MHC) restriction of the response to these antigens differed: clones recognizing the 18,000 MW antigen required antigen-presenting cells expressing DR1 subtype DRB1*0101 or DRB1*0102 which only differ at amino acids 85 and 86 on the DR beta-chain; by contrast clones recognizing the 30,000 MW antigen were presented to only by antigen-presenting cells from DRB1*0101 individuals, reflecting extreme sensitivity of these clones to the polymorphism at positions 85 and 86 on the DR beta-chain.

Characterization of kinetics and target proteins for binding of human complement component C3 to the surface-exposed outer membrane of Chlamydia trachomatis serovar L2

In order to characterize the interaction of human complement with Chlamydia trachomatis, flow cytometry was used to quantitate binding of complement component C3 to elementary bodies of C. trachomatis serovar L2 preincubated in fresh serum in the presence or absence of human polyclonal chlamydial antibody. Isolation of each of the complement activation pathways revealed that C3 was activated most effectively by the alternative pathway. The degree of binding by the classical pathway was proportional to the concentration of antibody, but dual-pathway-mediated binding was not greater than antibody-independent alternative pathway binding. Electrophoresis and immunoblotting of detergent-extracted outer membrane protein-C3b complexes indicated that the chlamydial major outer membrane protein was the primary cell surface moiety binding C3b in both the presence and absence of specific antibody. Hydroxylamine cleavage of outer membrane protein-C3b complexes provided evidence that the majority of C3b is bound to the major outer membrane protein by hydroxyl ester bonds. This result was also unchanged by the presence of specific antibody. An unexpected finding was the apparent binding of anti-C3 antibody to a 40-kDa protein of the chlamydial outer membrane complex, perhaps indicating C3 mimicry on the part of the chlamydial major outer membrane protein.

An intermolecular mechanism of T cell help for the production of antibodies to the bacterial pathogen, Chlamydia trachomatis

Antibodies that neutralize infectivity are directed at the antigenically variant major outer membrane protein (MOMP) of Chlamydia trachomatis. A vaccine for chlamydia will need to include T cell determinants that elicit T helper (Th) cells which provide help to MOMP-specific B cells. A limited number of determinants on MOMP are able to elicit Th cells and sequence diversity in the MOMP molecule may alter T cell recognition of these determinants. We investigated whether two sequence invariant proteins of C. trachomatis that are both abundant and immunogenic could elicit T cell help for the production of antibody to MOMP. We found that outer membrane protein 2 (OMP2) but not outer membrane protein 3 (OMP3) was able to prime BALB/c mice for an anamnestic anti-MOMP response following boost with the intact organism. This demonstration of an intermolecular mechanism of T cell help in a bacterial system has important implications for the development of a chlamydial vaccine as well as the design of vaccines for other antigenically variant non-viral pathogens.

Early complement components enhance neutralization of Chlamydia trachomatis infectivity by human sera

Immunoglobulin G in human serum neutralizes chlamydial infectivity in vitro. Complement-intact, C5-depleted, and C8-depleted human serum all have significantly more neutralizing activity than serum heated to inactivate early components of complement. Cobra venom factor, an analog of human C3b, enhances neutralization of antichlamydial immunoglobulin G in the absence of early complement components.

Immunoelectron microscopy of Chlamydia psittaci with monoclonal antibodies

An immunoelectron microscopic study was performed to determine the distribution of antigenic components on particles of Chlamydia psittaci and infected cells using a number of monoclonal antibodies (MAbs). Of three anti-lipopolysaccharide (LPS) antibodies (4D5, A2 and 4G5), two antibodies (4D5 and A2) reacted with the surface of reticulate bodies (RBs) but not with that of elementary bodies (EBs). The other antibody (4G5) reacted with both EBs and RBs. Examination of infected cells in thin sections revealed that 4D5 and A2 combined with the membranes of both EBs and RBs. These results indicate that each LPS epitope localized at a different position in the chlamydial membrane. Most MAbs directed to protein antigens reacted on the surface of both EBs and RBs though 3E9 specific for the 90 kDa and 50 kDa protein components combined with RBs only.

Functional and structural mapping of Chlamydia trachomatis species-specific major outer membrane protein epitopes by use of neutralizing monoclonal antibodies

Three monoclonal antibodies (MAbs), E4, L1-4, and L1-24, to the major outer membrane protein (MOMP) of Chlamydia trachomatis were identified that neutralized in vitro the infectivity of members of the B- and C-related complex as well as the mouse pneumonitis strain. MAbs L1-4, L1-24, and E4 gave a strong signal in an indirect immunofluorescence assay and/or Western immunoblot with all serovars of the lymphogranuloma venereum and trachoma biovars and a weak signal with the mouse biovar. In addition, C. psittaci and C. pneumoniae were also weakly recognized by MAbs L1-4 and L1-24. As determined by the technique of pneumoniae were also weakly recognized by MAbs L1-4 and L1-24. As determined by by the technique of overlapping peptides, all three MAbs showed reactivity to variable domain (VD) IV of MOMP. While all three MAbs had different recognition patterns, all strongly bound to the peptides TLNPTI and LNPTIA within the species-conserved region of VD IV. MAb E4 also recognized the peptide SATAIF in the subspecies region of VD IV. Peptides corresponding to VD IV of MOMP were synthesized and used in competitive inhibition experiments to determine the functional location of the epitope recognized by these three MAbs. Both the serological and neutralizing activities of MAb E4 were inhibited by the peptides ATAIFDTTTLNPTIAG and FDTTTLNPTIAG; however, none of the peptides made to the VD IV region blocked the neutralizing activity of MAbs L1-4 and L1-24. Therefore, the neutralizable domain of the epitope recognized by MAb E4 is contiguous and may be an important candidate for inclusion in a subunit vaccine.