Human genital antibody-mediated inhibition of Chlamydia trachomatis infection and evidence for ompA genotype-specific neutralization

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.

Human antibody signatures towards the Chlamydia trachomatis major outer membrane protein after natural infection and vaccination

“…Ardizzone et al. determined the NT 50 levels against SvD and SvIa in infected women using the A2EN cell line, 13 and Gupta et al. using Hep2 cells.…”

“…determined neutralisation titres in serum samples from 57 women diagnosed with genital CT infection of different genotypes and observed strong correlation between serum anti-elementary body (EB) IgG titres and neutralisation titres for SvD. 13 …”

A systems serology approach to the investigation of infection-induced antibody responses and protection in trachoma

“…Here, we found that antibody-dependent phagocytosis was somewhat higher in susceptible individuals, albeit only in the small subgroup for which this assay was performed. Furthermore, serum IgG from women with a recent urogenital C. trachomatis infection, or monoclonal antibodies against C. trachomatis , can, in some cases, enhance in vitro uptake of EBs, presumably via an Fc receptor on target cells ( 46 ). On the other hand, we found neutralizing antibodies to also be higher in susceptible individuals, and there was no evidence of increased C. trachomatis burden in secondary infections.…”

A Systems Serology Approach to the Investigation of Infection-Induced Antibody Responses and Protection in Trachoma

“…Like dengue, C. trachomatis is an intracellular pathogen with multiple circulating serovars, and here antibody-dependent phagocytosis was somewhat higher in susceptible individuals. Serum IgG from women with a recent urogenital C. trachomatis infection, or monoclonal antibodies against C. trachomatis , can in some cases enhance in vitro uptake of EBs, presumably via an Fc receptor on target cells (Ardizzone et al ., 2021). On the other hand, we found neutralizing antibodies to also be higher in susceptible individuals, and there was no evidence of increased C. trachomatis burden in secondary infections.…”