Further characterization of an outer membrane protein of Chlamydia trachomatis with cytadherence properties

To further characterize the chlamydial cytadhesin (CCA), we have examined it for saturability of binding to HeLa cells that were grown as monolayers and in suspension. The CCA exhibited specific cytadherence properties of binding to HeLa cells that appeared to be saturable. The CCA showed a substantial decrease in binding to trypsin-treated HeLa cells in suspension. This finding, together with the fact that the CCA itself is known to be trypsin-sensitive, suggested a protein-protein type of interaction between CCA and HeLa cells. Periodate treatment of the CCA did not result in significant reduction in cytadherence, which implies that sugar moieties were probably not involved in CCA binding to HeLa cells. Whilst attempts to produce antibodies to the CCA in rabbits was unsuccessful, the CCA reacted with antibodies in a human serum known to contain high titer antibodies to Chlamydia trachomatis, suggesting it can be immunogenic, and is possibly expressed during human infection.