Cell Wall Components and Antigenic Structure - Chlamydia trachomatis

Cell Wall Components and Antigenic Structure

Chlamydiae possess three types of major antigens: (a) genus-specific antigens, (b) species-specific antigens, and (c) serotype-specific antigen.

◗ Genus-specific antigen

This is a heat-stable, complement-fixing, and genus-specific antigen. It is an LPS–protein complex resembling the LPS of Gram-negative bacilli. It is present in EBs and RBs. The antigen can be extracted by ether, chloroform, or methanol. The anti-gen is identified by CFT.

◗ Species-specific antigen

This antigen is present at the envelope surface and is species specific. This antigen is present in all the strains of Chlamydia.

◗ Serotype-specific antigen

This antigen is present only in a few species of chlamydiae. They are located in the major outer membrane proteins (MOMPs) and are useful for intraspecies typing of Chlamydia species.

◗ Typing of species

On the basis of these antigens, Chlamydia species are classi-fied into various serovars and serologic variants. C. trachomatis has been subdivided into three biological variants known as biovars: (a) trachoma biovar causing trachoma and inclusion conjunctivitis (TRIC), (b) lymphogranuloma venereum (LGV) biovar causing LGV, and (c) serovars causing mouse pneumo-nitis. These biovars on the basis of antigenic differences in the MOMPs have been further classified into 20 serotypes. The trachoma biovar consists of 13 serotypes (A, B, Ba, C, D, Da, E, F, G, H, I, Ia, J, Ja and K). The LGV biovar consists of only five serotypes (L1, L2, L2a, L2b, and L3).