Figure 6.

Activated platelets are essential for recombinant Staphylococcus aureus α-hemolysin (rSa-AH)–mediated platelet-neutrophil aggregate (PNA) formation. To examine the relative contribution of each cell type to PNA formation, isolated, gel-filtered platelets were exposed to rSa-HA (2.5 hemolytic units [HU]) for 8 minutes and then combined with unstimulated isolated polymorphonuclear leukocytes (PMNLs) for 2 min, or vice versa, and PNA formation was assessed as described in Figure 1. As controls, isolated cells were incubated together in the presence of rSa-HA for the indicated times. PNA formation above baseline only occurred when platelets were preactivated with α-hemolysin; preactivation of PMNLs with rSa-HA for 8 minutes did not stimulate aggregate formation. *P < .05, by the Student t test. Abbreviation: DPBS, Dulbecco's phosphate-buffered saline.