Mode of entry and release of chlamydiae in infections of intestinal epithelial cells.

The uptake and release of chlamydiae in infections of highly specialized intestinal, absorptive epithelial cells of the ileum of newborn calves were studied. Infection occurred only through the brush border of the enterocytes. The chlamydial elementary bodies were adsorbed onto the microvilli, a process that induced pinocytosis of the elementary bodies and formation of endosomes containing one dense-centered chlamydial form. The endosomes moved towards the supranuclear region of the enterocytes, and the cell membrane entrapping the chlamydial agent gradually dissolved so that inclusions with reticulate and dense-centered forms appeared to be free in the cytoplasm. After replication, chlamydiae were shed into the intestinal lumen in three different ways. Some infected enterocytes ruptured and liberated their contents into the lumen. In other instances, entire infected cells were extruded into the lumen, where their membranes degenerated to release chlamydial forms. In the third mode of release, chlamydiae were liberated in cytoplasmic fragments surrounded by cell membranes.