Examination of chlamydial glycolipid with monoclonal antibodies: cellular distribution and epitope binding

A chlamydial glycolipid antigen (GLXA) is shed into the medium of C. trachomatis-infected cell cultures. This study screened monoclonal antibodies (mAb), prepared in different laboratories by immunization with embryonated egg propagated elementary bodies (EB), for their ability to bind with infected cells and to react with purified GLXA isolated from supernatants of infected McCoy cells. The fluorescent antibody (FA) staining pattern exhibited by a number of mAb indicated that they bound antigen present within the inclusion and at the inner membrane surface of infected cells; the observed pattern differs significantly from the distribution seen when anti-lipopolysaccharide (LPS) (mAb) were used. The staining pattern observed by immunofluorescence was confirmed and extended by ultrastructure studies of immunogold-labelled, infected human endometrial gland epithelial cells (HEGEC) and a human endometrial carcinoma-derived cell line (RL95-2). Additionally, the immunoelectron microscope studies revealed binding within the inclusion and on reticulate bodies, within the cell cytoplasm and at the surface of infected cells. The specificity of the reactive mAb, examined by molecular shift chromatography and isolated, affinity-purified GLXA, indicated that two mAb of the IgG isotype recognized an antigen which had been purified from tissue culture supernatants by affinity chromatography using an IgM mAb. The results suggest that GLXA is an important determinant whose role and function during in vitro and in vivo infections deserves further analyses.