Interference of Staphylococcus aureus lipase with human granulocyte function.

The influence of purified Staphylococcus aureus lipase on granulocyte function and morphology was studied. The lipase itself was strongly chemotactic; in addition preincubation of granulocytes with low concentrations of lipase enhanced the directed movement, as assayed in the agarose system. Higher concentrations of lipase, in contrast, gave a progressive reduction of granulocyte chemotaxis; at 12 micrograms lipase per ml, cells were almost immobilized. Phagocytic killing of Staphylococcus aureus by granulocytes preincubated with lipase was reduced in a dose-dependent manner. At 12 micrograms lipase per ml almost no staphylococcal killing occurred. This was mainly accounted for by a reduction of bacterial uptake, but some decrease in intragranulocytic killing was also noted. These functional alterations, which can all be ascribed to an interference with membrane functions, were associated with marked changes of the granulocyte surface structure, which was denuded and lacked normal microvilli. The effects of lipase were partly retained after heat inactivation of lipase activity, indicating that the effects of staphylococcal lipase on granulocyte function are not due to enzymatic activity alone. These effects of lipase may be an important virulence factor and contribute to the preferential location of lipase-producing Staphylococcus aureus strains at deep sites of infection.