Delivery of azithromycin to Chlamydia trachomatis-infected polarized human endometrial epithelial cells by polymorphonuclear leucocytes

An in-vitro model was designed to evaluate whether polymorphonuclear leucocytes (PMN) loaded with azithromycin could migrate and deliver the antibiotic in a bioactive form to chlamydia inclusions in polarized human endometrial epithelial (HEC-1B) cells infected with Chlamydia trachomatis. PMN chemotaxis through the extracellular matrix and between infected epithelial cells was readily observed if the HEC-1B cells had been infected with chlamydiae for 36 or 48 h. Inclusions in infected epithelial cells exposed to PMN loaded with azithromycin were initially distinguished by deformed reticulate bodies and an excessive amount of chlamydial outer membrane vesicles. As the amount of PMN-delivered antibiotic increased, chlamydial inclusions were filled with large cell envelope 'ghosts' which were the remnants of lysed reticulate bodies. The lethal effect of azithromycin was confirmed by a reduction in the viability of infectious progeny. Our results demonstrate that the damage to chlamydiae was due to transport and delivery of azithromycin by PMN to infected genital epithelial cells. When infected HEC-1B cells were exposed to PMN not loaded with the antibiotic, chlamydial morphology was not obviously affected yet few viable progeny could be recovered. In this case, PMN-induced damage to host epithelial cells probably interrupted chlamydial nutrient acquisition and subsequent maturation and formation of infectious progeny.