Interaction of chlamydiae with host cells and mucous surfaces.

For chlamydiae, as obligate intracellular parasites, attachment to and ingestion by host cells are essential steps in reproduction. Their attachment site appears to be heat-sensitive; it has not been correlated with any morphological entity. Antibody blocks chlamydial attachment to cells and, for certain chlamydia psittaci and chlamydia trachomatis strains which are highly infective for cell cultures, N-acetylglucosamine appears to contribute to cell receptor specificity. Sialic acid residues have been suggested as receptors for other C. trachomatis strains. The guinea-pig inclusion conjunctivitis strain of C. psittaci becomes associated with the conjunctiva during incubation of inoculated tissue fragments in vitro. However, although antibody from tears neutralizes infectivity of this strain in vivo, association of the organism with tissue fragments is not inhibited, suggesting that antibody neutralization in vivo is not mediated by prevention of attachment to cells. Chlamydial infectivity for cell monolayers is greatly increased by centrifugation. The process is temperature-dependent and involves cooperative interactions between direction force and the pressure generated during centrifugation. Enhanced infectivity appears to result from changes induced in the cell surface. These changes may favour nonspecific interactions in attachment, since antibody inhibition of infectivity on static cell monolayers is overcome by centrifugation.