Antigens of Chlamydia trachomatis

Chlamydia trachomatis is an obligate intracellular parasite that elaborates antigens on its surface. These antigens are divided into genus-, species-, subspecies-, and serovar-specific determinants. The genus, or group antigen(s), are lipopolysaccharides similar to those found in gram-negative bacteria and a glycolipid that is secreted by infected cell cultures. Species-specific antigens differentiate Chlamydia trachomatis from Chlamydia psittaci and are expressed on the outer membrane. These proteins range in molecular weight from 155,000 to approximately 40,000. Monoclonal antibodies to outer-membrane proteins have demonstrated the presence of subspecies-reactive antigenic determinants. Type-specific antigens are associated with the major outer-membrane protein and are secreted from infected cells as well. The molecular weights of these proteins range from 30,000 to 40,000. These antigens may participate in the binding of the organism to target cells and in an enzymatic process of some type that initiates endocytosis. The significance of the soluble antigens detected in the microenvironment in vitro may suggest immune-complex formation, a process that could contribute to the immunopathology of the disease.