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

Abstract

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 L-929 cells with the cytoskeleton agents colchicine or cytochalasin B or with Nethylmaleimide 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.

Lipids in host–pathogen interactions: Pathogens exploit the complexity of the host cell lipidome

“…Also various Rickettsia species lyse their phagosomal compartment after entry into a host cell. The lysis of the vacuolar membrane has been attributed to the activity of rickettsia PLA 2 [57,58,73]. The failure to identify a rickettsia PLA 2 from the rickettsia genome, together with the identification of a PLD in R. prowazekii and R. conorii has led to the suggestion that a PLD is involved in the escape from the vacuole [74].…”

Some lessons fromRickettsiagenomics

“…This pathway is induced upon phagocytosis of some microorganisms in response to the nutrient starvation in the phagosome [26]. Rickettsiae rapidly escape from this compartment by dissolving the phagocytic vesicle surrounding them [27]. Thus, the utilization of this simple carbon source might not be necessary for these bacteria to survive in the host cell cytoplasm.…”

“…Uptake of Rickettsia also requires participation of the parasitized host as it is mediated by an induced phagocytosis process [92,93]. A rickettsial phospholipase A 2 (PLA 2 ) has been proposed to mediate escape from phagosomes [27,94]. PLA 2 activity was also associated in part with the hemolytic activity of R. prowazekii [95].…”

Rickettsioses of the Spotted Fever Group around the World

“…Host-mediated pathogenic mechanisms such as immunopathology and coagulation-mediated injury do not appear to be significant (26-28). Cell injury by rickettsiae has been associated with phospholipase A activity, protease activity, and free radical-induced lipid peroxidation (29)(30)(31)(32)(33). Which of these or other mechanisms are most important and whether some or all may be involved in a sequential series of pathogenic events remains to be determined.…”