Rickettsia rickettsii has proteins with cross-reacting epitopes to eukaryotic phospholipase A2 and phospholipase C

The entry, and possibly the exit, of rickettsiae from eukaryotic cells, as well as erythrocyte lysis by some members of this group of organisms, is thought to be mediated by a phospholipase A activity even though the enzyme has not been isolated from these organisms. Evidence for phospholipase C, on the other hand, has not been reported for the genus Rickettsia. In this study, in a preliminary attempt to demonstrate the presence of phospholipase A2 and phospholipase C in the virulent Sheila Smith strain of Rickettsia rickettsii, we performed immunoblotting and immuno-gold electron microscopy using anti-phospholipase A2 and anti-phospholipase C IgG antibodies (raised against mammalian enzymes). We provide evidence for cross-reactivity of the antibodies with proteins present in R. rickettsii. Western blots showed a higher staining intensity with anti-phospholipase C antibody than with anti-phospholipase A2. According to the results obtained with the immuno-gold labeling of phospholipase A2 and phospholipase C reactive epitopes, most of the phospholipase A2 cross-reactive material appears to be associated with the membrane of the organism while the phospholipase C cross-reactive material appears to be randomly distributed throughout the cell.