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Neutrophils (PMN) and group IIA phospholipase A2 (gIIA PLA2) are components of the innate immune system mobilized to sites of invasion by microorganisms such as Staphylococcus aureus. Although accumulating coincidentally in vivo, the in vitro anti-staphylococcal activities of PMN and gIIA PLA2 have thus far been separately studied. The goal of this thesis was to study the collaborative activity of PMN and gIIA PLA2 against S. aureus.
We have identified and characterized the collaboration of PMN and gIIA PLA2 against S. aureus ingested by PMN. PMN induced conversion of bacterial phosphatidylglycerol into cardiolipin, but were unable to degrade S. aureus phospholipids without gIIA PLA2. PMN reduced by 10-fold the concentration of gIIA PLA2 needed to digest bacterial phospholipids alone.
In addition to increased phospholipid degradation, collaboration of PMN and gIIA PLA2 caused greater bacterial killing and greater loss of bacterial green fluorescent protein fluorescence. The collaboration of PMN and gIIA PLA2 against S. aureus is dependent on catalytic activity and is specific to gIIA PLA2 as related secretory PLA2, groups IB, V, and X, show little or no phospholipid degradation of S. aureus either alone or in the presence of PMN. Synergy of PMN and gIIA PLA2 requires a functional NADPH oxidase and phagocytosis. Although addition of gIIA PLA2 after phagocytosis causes some bacterial phospholipid degradation, the greatest effect is observed when gIIA PLA2 is added before phagocytosis.
An extracellular source of H2O2 can partially restore antibacterial activities to NADPH oxidase deficient PMN including the ability to collaborate with gIIA PLA2, supporting a role for reactive oxygen species in NADPH oxidase dependent antimicrobial functions of PMN. In contrast, iberiotoxin, an inhibitor of BK potassium channels had no effect of PMN antibacterial activities. Although H2O2 partially restored antibacterial activity to NADPH oxidase deficient PMN, extracellular H2O2 was not sufficient to increase S. aureus to gIIA PLA2 activity.
In summary, PMN and gIIA PLA2 collaborate against S. aureus. These findings revealed collaboration between cellular oxygen-dependent and extracellular oxygen-independent host defense systems that may be important in the ultimate resolution of S. aureus infections.