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.

Fig 1. Mucosal antibodies isolated from the genital tract of women diagnosed with Ct infection inhibit C. trachomatis infection in vitro.

Percent inhibition of infection of C. trachomatis D/UW-3/Cx in A2EN cells following incubation with IgG or IgA isolated from serum or CVL of patients diagnosed with C. trachomatis infection. IgG and IgA were tested at 5 ng/ml concentrations of anti-Ct antibody. Horizontal bars represent mean percent inhibition of infection. Kruskal-Wallis test followed by Dunn’s post-test, *p<0.05; **p<0.01; ***p<0.001.

Fig 2. Genital antibody-dependent inhibition of C. trachomatis infection is influenced by the genotype and serogroup of the infecting strain.

(A) Relative abundance of ompA genotypes. (B) Consensus phylogenetic tree of aligned ompA gene sequences amplified from C. trachomatis clinical isolates. Numbers on tree represent individual patients. Letters on tree (Sv D-K, Da, Ia, Ja) indicate the genotype of each cluster of clinical isolates. (C-J) Percent inhibition of infection of C. trachomatis D/UW-3/Cx in A2EN cells following incubation with IgG or IgA purified from serum or CVL of patients diagnosed with C. trachomatis infection. (C, E, G, I) Patients grouped by genotype of infecting strain. (D, F, H, J) Patients grouped by serogroup of infecting strain. Points represent individual patients. Grey dots indicate isotype controls. Bars represent mean percent inhibition of infection. (C-J) Kruskal-Wallis test followed by Dunn’s post-test, *p<0.05; **p<0.01; ***p<0.001, ****p<0.0001.

Fig 3. Serum antibody-dependent inhibition of C. trachomatis infection is influenced by both EB-specific IgG concentration and ompA genotype of the infecting strain.

(A) Serum neutralizing antibody titers (ID₅₀) to D/UW-3/Cx with patients grouped by infecting serovar. (B) Serum neutralizing antibody titers to D/UW-3/Cx with patients grouped by serogroup of infecting strain. (C) Scatter plot of serum ID₅₀ values against D/UW-3/Cx plotted against concentrations of EB-specific IgG in patient serum. (D) Serum ID₅₀ values against Ia/LSU-56/Cx with patients grouped by serovar of infecting strain. (E) Serum ID₅₀ values against Ia/LSU-56/Cx with patients grouped by serogroup of infecting strain. (F) Scatter plot of serum ID₅₀ values against Ia/LSU-56/Cx plotted against concentrations of EB-specific IgG in patient sera. Points represent individual patients. Grey dots indicate patients that spontaneously cleared C. trachomatis infection. The point with an "X" denotes a patient for which the ompA genotype could not be determined. Dotted lines denote starting serum dilution. (A,B,D,E) Kruskal-Wallis test followed by Dunn’s post-test, *p<0.05; **p<0.01; ***p<0.001. (C,F) Spearman’s rank-order correlation.