Chlamydia trachomatis is an obligate intracellular pathogen.
Infection of susceptible individuals with this bacterium can trigger the development of
reactive arthritis, an acute
inflammation that is associated with the expression of the
class I major histocompatibility antigen,
HLA-B27. Other facultative intracellular pathogens, such as Yersinia and Salmonella spp., are also known triggers of
reactive arthritis. Previous studies report conflicting results concerning whether the presence of
HLA-B27 modulates the
infection of cells with these enteric pathogens. In the present study, we have examined whether the expression of
HLA-B27 can influence the
infection of cell lines with C. trachomatis and also whether the replication of these bacteria is altered in HLA-B27-expressing cell lines. To do this, we have used a sensitive flow cytometric approach. We fixed and permeabilized cells and used
fluorescein isothiocyanate-conjugated
monoclonal antibody specific for chlamydia
lipopolysaccharide to detect intracellular bacteria. The staining pattern obtained closely resembled the intracellular life cycle of chlamydia, with the appearance of brightly staining cells correlating to the microscopic detection of mature inclusion bodies. Moreover, since the percentage of cells that stained with the antibody was proportional to the infectious inoculum used, we were able to use the technique to quantitate the number of infectious organisms recoverable from infected cell lines. An important component of our study was the use of
heparin to prevent
reinfection of cells and thus enable the
infection to be followed from a discrete time point. Our results suggest that
HLA-B27 influences neither the
infection nor replication of C. trachomatis serovar L2 within cell lines. Consequently, the role of
HLA-B27 in the pathogenesis of
reactive arthritis may lie downstream of the invasion and replication stages of the triggering pathogenic
infection.