Cross-linking of Fc gamma receptor IIa and Fc gamma receptor IIIb induces different proadhesive phenotypes on human neutrophils.

Activation of polymorphonuclear leukocytes (PMN) plays an important role in vascular injury associated with systemic vasculitis and in models of autoantibody- and immune complex-mediated disease. The potential role of intravascular activation of PMN, however, is confounded by the observation that some stimuli injected i.v. (e.g., IL-8 and C5a) lead to L-selectin shedding by PMN, which inhibits attachment to endothelium and may be functionally anti-inflammatory. To explore the impact of Fc gamma receptor (Fc gamma R)-mediated activation on the PMN adhesive phenotype, Fc gamma RIIa (CD32) and Fc gamma RIIIb (Cd16) were targeted with receptor-specific reagents, and the expression of adhesion molecules-mediating rolling (L-selectin) and firm adhesion (CD11b/CD18) was measured. Engagement of either Fc gamma RIIa or Fc gamma RIIIb leads to activation, demonstrated by degranulation (upregulation of CD66b), and to increased expression of total CD11b/CD18 and functional CD11b/CD18 (I-domain). In contrast, L-selectin shedding induced by PMN Fc gamma R was divergent. Despite the 5- to 10-fold greater expression and engagement at saturation, activation via Fc gamma RIIIb led to little or no change in L-selectin expression. Stimulation of PMN with intact murine anti-receptor IgG1 showed a contribution of Fc gamma RIIa receptor polymorphisms, underscoring the direct influences of Fc gamma R allotypes on receptor function. These observations suggest that Fc gamma RIIIb-mediated activation of circulating PMN may lead to a proadhesive phenotype likely to promote systemic vascular damage. This Fc gamma R-mediated adhesive phenotype will vary with the receptors engaged and their allotypes, which, in turn, reflect properties of the immune complex and the genetics of the host.