Abstract
The endocervix, the primary site of Chlamydia trachomatis (Ct) infection in women, has a unique repertoire of locally synthesized IgG and secretory IgA (SIgA) with contributions from serum IgG. Here, we assessed the ability of genital and serum-derived IgG and IgA from women with a recent positive Ct test to neutralize Ct elementary bodies (EBs) and inhibit inclusion formation in vitro in human endocervical epithelial cells. We also determined if neutralization was influenced by the major outer membrane protein (MOMP) of the infecting strain, as indicated by ompA gene sequencing and genotyping. At equivalent low concentrations of Ct EB (D/UW-3/Cx + E/UW-5/Cx)-specific antibody, genital-derived IgG and IgA and serum IgA, but not serum IgG, significantly inhibited inclusion formation, with genital IgA being most effective, followed by genital IgG, then serum IgA. The well-characterized Ct genotype D strain, D/UW-3/Cx, was neutralized by serum-derived IgG from patients infected with genotype D strains, genital IgG from patients infected with genotype D or E strains, and by genital IgA from patients infected with genotype D, E, or F strains. Additionally, inhibition of D/UW-3/Cx infection by whole serum, rather than purified immunoglobulin, was associated with levels of serum EB-specific IgG rather than the genotype of infecting strain. In contrast, a Ct genotype Ia clinical isolate, Ia/LSU-56/Cx, was neutralized by whole serum in a genotype and genogroup-specific manner, and inhibition also correlated with EB-specific IgG concentrations in serum. Taken together, these data suggest that (i) genital IgA most effectively inhibits Ct infection in vitro, (ii) human antibody-mediated inhibition of Ct infection is significantly influenced by the ompA genotype of the infecting strain, (iii) the genital antibody repertoire develops or matures differently compared to systemic antibody, and (iv) ompA genotype-specificity of inhibition of infection by whole serum can be overcome by high concentrations of Ct-specific IgG.
Highlights
With over 124 million annual global infections, Chlamydia trachomatis (Ct) remains the most common sexually transmitted bacterial infection [1]
This study utilized IgG and IgA purified from cervicovaginal lavage (CVL) and serum samples from a cohort of fifty-seven women who were recently diagnosed with genital Ct infection by a standard nucleic acid amplification test (NAAT) (Hologic1 APTIMA1) and were returning to the clinic for antibiotic treatment
EBspecific antibodies in the IgG and IgA preparations purified from CVL were not measured due to their limited amount
Summary
With over 124 million annual global infections, Chlamydia trachomatis (Ct) remains the most common sexually transmitted bacterial infection [1]. A vaccine is required for mass protection, but advances have been cautioned by the knowledge that pathology is immune-mediated [7]. We believe there is a great need for studies to define what constitutes both a safe and protective immune response to Ct. Animal models, while limited in recapitulating all elements of Ct infection in the human genital tract, have informed key immune responses likely required for immunity against Chlamydia spp. In vitro modeling has revealed potential mechanisms by which murine antibodies can inhibit Chlamydia infection, indicating that antibody isotype, in addition to antigen specificity, dictates functional outcomes. Uninfected A2EN cells and Ct infected cells without antibodies were performed in triplicate for each plate. Inclusions and nuclei were visualized at 20X using a Zeiss Observer.Z1 microscope, and triplicate pictures of each sample were captured using ZEN 2.3 Pro software. Nuclei were enumerated using CellProfiler 3.1.5, and inclusions were enumerated using ImageJ 2.0
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