Interaction between Chlamydia spp. and human polymorphonuclear leukocytes in vitro

Chlamydia psittaci and Chlamydia trachomatis elementary bodies (EB) incubated in the presence of complement or specific antibody or both caused chemotaxis of human polymorphonuclear leukocytes (PMN) in vitro. Reticulate bodies and culture supernatants had no effect on these cells. The ability of chlamydiae to enter and survive in PMN under nonopsonizing conditions was investigated by measuring the association of 3H-labeled EB and of inclusion-forming units with these phagocytes. Both assays indicated that C. psittaci as well as C. trachomatis EB are efficiently internalized. The mechanism by which this is accomplished is distinct from classical phagocytosis in that it is not dependent upon the presence of complement or antibody. Furthermore, uptake of at least C. psittaci appeared to be rapid, with no additional increase occurring after 15 min. The majority of cell-associated chlamydiae were rendered acid soluble or noninfectious within 1 h. Subsequently, there was a small but steady loss of infectivity for up to 10 h, which may have been due to the conversion of EB to the noninfectious reticulate-body form of the organism. However, even at 10 h after entry a small percentage of bacteria was still capable of infecting a second target cell. This is noteworthy in that PMN are relatively short-lived cells, and after lysis, intracellular organisms may be free to infect adjacent tissue. Electron microscopic observations were consistent with the data on uptake and persistence. The ability of a small percentage of infecting chlamydiae to maintain infectivity in PMN for at least several hours may enable these organisms subsequently to establish productive infection in permissive host cells.