The interaction of Chlamydia trachomatis with host cells: ultrastructural studies of the mechanism of release of a biovar II strain from HeLa 229 cells.

Serotypes of Chlamydia trachomatis classified as biovar II strains (immunotypes A, Ba, and B-K) are currently recognized as important human pathogens that produce disease characterized by a rather complex pathogenesis. We have studied some morphological phenomena in the interaction of C. trachomatis (strain UW3/Cx, serotype D) with HeLa 229 cells to define the mechanisms of release of these obligate intracellular parasites. Fluorescent-antibody staining of unfixed HeLa cells infected with chlamydiae suggested that this biotype of C. trachomatis can exit cells without concomitant death of the host cell. The mechanisms by which chlamydiae were released from cells were studied by scanning and transmission electron microscopy. Ultrastructural observations indicated that the chlamydial inclusion was segregated from host cytoplasm and transported to the host cell surface by a process similar to exocytosis. These observations of interactions between C. trachomatis and the host cell in vitro may be relevant for understanding the complex pathogenesis these organisms produce in vivo, specifically their ability to produce asymptomatic or latent infections.