Chlamydia Trachomatis Infection Elicits Distinct Profiles of T Cell Phenotypes in Systemic Versus Mucosal Sites

Background:  Our understanding of the immune responses and immune cells in Chlamydia trachomatis (CT) infection primarily comes from animal models. However, these immune mechanisms have yet to be fully elucidated in humans. There are sparse human studies on chemokine receptor expression during CT infection. In this study, our objective is to phenotypically delineate systemic and mucosal T cell subsets from a uniquely characterized cohort of healthy women with CT infection. 

Methods:  Using flow cytometry, we evaluated T cell subsets in samples from 3 patient groups: 1) peripheral blood mononuclear cells (PBMCs) from 96 CT-infected women (NAAT positive), 2) PBMCs from 6 CT seronegative healthy controls, and 3) matched mucosal mononuclear cells (MMCs) and PBMCs from 13 CT-infected women. T cell phenotype comparisons from unpaired PBMC samples were evaluated using the Wilcoxon rank-sum test. T cell phenotypes in paired MMCs and PBMCs were analyzed using the Wilcoxon sign-rank test. 

Results:  We found higher homing receptor expression (CXCR3, CCR5, CCR4 and CCR7) on peripheral blood and mucosal T cells (CD4+ and CD8+) in CT infected women compared with CT seronegative controls. Among CT infected women, mucosal T cells expressed higher CD38 and HLA-DR levels as well as CXCR3 levels when compared to peripheral blood T cells.

Conclusions:  Higher homing receptor expression in CT infected women compared with CT seronegative controls suggests active migration of T cells towards the mucosal site of infection. There was a higher expression of T cell activation markers in the genital mucosa compared with peripheral blood, likely in part because this is the site of active infection.