DISTRIBUTION OF ENDOSOMAL, LYSOSOMAL, AND MAJOR HISTOCOMPATIBILITY COMPLEX MARKERS IN A MONOCYTIC CELL-LINE INFECTED WITH CHLAMYDIA-PSITTACI

The intracellular fate of Chlamydia psittaci during infection of a mon ocytic cell line, THP1, was characterized. Cytochalasin D inhibited ph agocytosis of latex beads but had no effect on infection by C. psittac i, and vacuoles expressed the transferrin receptor, suggesting accessi bility to the endocytic pathway, Early Chlamydia-containing vacuoles e xpressed major histocompatibility complex (MHC) class I molecules, and most vacuoles fused with host cell lysosomes, since they expressed LA MP-1 and had acidic pHs. In cells prestimulated with gamma interferon, vacuoles also expressed MHC class II molecules, suggesting that the m onocytes might effectively process Chlamydia-derived antigens for pres entation by MHC class I and class II molecules.