Differences in susceptibilities of the lymphogranuloma venereum and trachoma biovars of Chlamydia trachomatis to neutralization by immune sera

Chlamydia trachomatis L2c Infection in a Porcine Model Produced Urogenital Pathology and Failed to Induce Protective Immune Responses Against Re-Infection

The current study was designed to evaluate the pathogenesis, pathology and immune response of female genital tract infection with Chlamydia trachomatis L2c, the most recently discovered lymphogranuloma venereum strain, using a porcine model of sexually transmitted infections. Pigs were mock infected, infected once or infected and re-infected intravaginally, and samples were obtained for chlamydial culture, gross and microscopic pathology, and humoral and cell-mediated immunity. Intravaginal inoculation of pigs with this bacterium resulted in an infection that was confined to the urogenital tract, where inflammation and pathology were caused that resembled what is seen in human infection. Re-infection resulted in more severe gross pathology than primary infection, and chlamydial colonization of the urogenital tract was similar for primary infected and re-infected pigs. This indicates that primary infection failed to induce protective immune responses against re-infection. Indeed, the proliferative responses of mononuclear cells from blood and lymphoid tissues to C. trachomatis strain L2c were never statistically different among groups, suggesting that C. trachomatis-specific lymphocytes were not generated following infection or re-infection. Nevertheless, anti-chlamydial antibodies were elicited in sera and vaginal secretions after primary infection and re-infection, clearly resulting in a secondary systemic and mucosal antibody response. While primary infection did not protect against reinfection, the porcine model is relevant for evaluating immune and pathogenic responses for emerging and known C. trachomatis strains to advance drug and/or vaccine development in humans.

Specific-pathogen-free pigs as an animal model for studying Chlamydia trachomatis genital infection

The purpose of the present study was to evaluate pigs as a large-animal model for female genital infection with two Chlamydia trachomatis human serovar E strains. Sixteen-week-old specific-pathogen-free female pigs (gilts) were intravaginally infected with the trachoma type E reference strain Bour or the urogenital serovar E strain 468. Several conclusions can be drawn from our findings on the pathogenicity of a primary C. trachomatis genital infection in gilts. First of all, we demonstrated that the serovar E strains Bour and 468 could ascend in the genital tract of gilts. The serovar E strains could replicate in the superficial columnar cervical epithelium and in the superficial epithelial layer of the uterus, which are known to be the specific target sites for a C. trachomatis genital infection in women. Second, inflammation and pathology occurred at the replication sites. Third, the organisms could trigger a humoral immune response, as demonstrated by the presence of immunoglobulin M (IgM), IgG, and IgA in both serum and genital secretion samples. Our findings imply that the pig model might be useful for studying the pathology, pathogenesis, and immune response to a C. trachomatis infection of the genital system.

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.

Some aspects of the immune response of koalas (Phascolarctos cinereus) and in vitro neutralization of Chlamydia psittaci (koala strains)

Western-blot analysis was used to study the reaction of koala antisera, two specific polyclonal antibodies and one monoclonal antibody, with chlamydial antigens in koalas infected with Chlamydia psittaci. The koala sera recognized four C. psittaci surface antigens, corresponding to the major outer membrane protein (39.5 kDa), 31 kDa protein, 18 kDa protein and lipopolysaccharide. The S25-23 LPS specific monoclonal antibody inhibited chlamydial infection (55-67%) with both koala strains (type I and type II). Both koala antiserum and rabbit polyclonal antibodies against either type of chlamydia significantly reduced the number of infected cells resulting from type II infections at a dilution of 1 in 20. Rabbit antiserum against type II was effective in neutralizing infection by type II elementary bodies, but was less effective against type I infection. In addition, no koala antiserum was effective in neutralizing type I infection.

Characterization of the humoral response induced by a peptide corresponding to variable domain IV of the major outer membrane protein of Chlamydia trachomatis serovar E

A 30-amino-acid peptide corresponding to variable domain IV (VD IV) of the major outer membrane protein of Chlamydia trachomatis serovar E was conjugated to keyhole limpet hemocyanin (KLH) and used to immunize mice. The resulting antisera (anti-KLH-VD IV sera) recognized all 15 serovars of C. trachomatis when assayed by indirect immunofluorescence and Western blotting. Probing of overlapping hexameric peptides representing VD IV with mouse anti-KLH-VD IV sera revealed that two main regions of the peptide were recognized by the antisera, the N terminus of the peptide, which contains B-complex-specific epitopes, and the middle region of the peptide, which contains a species-conserved domain. When used in an in vitro neutralization assay, these antisera were able to neutralize mainly serovars in the B complex. These data provide evidence that a linear peptide corresponding to VD IV can induce in vitro protection from C. trachomatis infectivity that is subspecies specific.

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.