Phospholipase A and the interaction of Rickettsia prowazekii and mouse fibroblasts (L-929 cells).

L-929 cells were killed when approximately 50 viable Rickettsia prowazekii organisms per L-cell were centrifuged onto a monolayer. The glycerophospholipids of the L-cell were hydrolyzed to lysophosphatides and free fatty acids. Concomitantly, there was a loss of membrane integrity as shown by release of lactate dehydrogenase and 86Rb and permeability to trypan blue dye. No glycerophospholipid hydrolysis or cytotoxicity occurred when the rickettsiae were inactivated by heat, UV irradiation, N-ethylmaleimide, or metabolic inhibitors before their addition to the L-929 cells. On the other hand, treatment of the L929 cells with the cytoskeleton agents colchicine or cytochalasin B or with N-ethylmaleimide inhibited neither the phospholipase A activity nor the loss of membrane integrity. Cytochalasin B-treated cells could be damaged by even small numbers of rickettsiae. We suggest that this phospholipase A activity is used by the rickettsiae to escape from the phagosomes into the cytoplasm of host cells.