Functional Analysis of the Polymorphic Membrane Protein Family of Chlamydia

Abstract

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen and the leading cause of infectious blindness. It is an obligate intracellular pathogen that has a biphasic lifecycle encompassing infectious elementary bodies (EBs) and metabolically active reticulate bodies (RBs). C. trachomatis encodes a polymorphic membrane protein (Pmp) gene family whose nine members are differentially expressed under in vitro growth conditions. The observed "phase-variation-like" phenotype of the autotransported Pmps is consistent with observed variable Pmp subtype-specific antibody profiles in patients infected with C. trachomatis. The autotransported Pmps display repeated, often alternating motifs GGA(I,L,V) and FXXN within the predicted "passenger" domain that have been proposed to mediate adhesion of Chlamydia pneumoniae to susceptible cells. The identification of a "magic bullet" adhesin responsible for attachment and subsequent internalization by epithelial cells has eluded researchers for several decades, owing to the inherent difficulties of the Chlamydia system, in particular the genetic intractability of these organisms. Others have established that Pmps of C. pneumoniae and PmpD of C. trachomatis function as adhesins and that PmpD-specific antibodies block attachment. I hypothesize that antibodies against each of the six Pmp subtypes (A, B/C, D, E/F, G/I & H) can neutralize a C. trachomatis infection, and that the application of multiple Pmp subtype-specific antibodies will have a cumulative negative impact on infection. I additionally hypothesize that Pmps of C. trachomatis facilitate adhesion to epithelial cells. For Aim 1, I will investigate the neutralizing effects of single Pmp subtype-specific antibodies by infecting epithelial cells with C. trachomatis serovar E EBs that have been preincubated with antibodies against each of the Pmp subtypes. The inclusions will be visualized using immunofluorescence. For Aim 2, I will investigate Pmp-mediated adherence to epithelial cells using a Pmp-coated latex bead-binding assay. The neutralization assay results cast doubt on the ability of Pmp-specific antibodies to neutralize a chlamydial infection on their own. It is possible that the Pmp-specific antibodies are necessary for complete neutralization, but are not sufficient. Additionally, the adhesion assay results suggest that other functions of Pmps should still be considered, however, their role in adhesion should not be ruled out.