The Atypical Zeta (ζ) Isoform of Protein Kinase C Regulates CD11b/CD18 Activation in Human Neutrophils

Objective: The objective of this study was to examine the role of protein kinase C zeta (PKCζ) in interleukin (IL)‐8‐mediated activation of Mac‐1 (CD11b/CD18) in human neutrophils. Materials and Methods: Neutrophils were stimulated with IL‐8 in the presence or absence of pharmacologic inhibitors of PKC or a myristoylated PKCζ pseudosubstrate. The resulting changes in Mac‐1 surface expression, affinity, and avidity, as measured by clustering, were determined by using a combination of flow cytometry and immunofluorescence (IF). Colocalization of Mac‐1 with PKCζ was also probed using IF. Finally, neutrophil adhesion to matrix proteins was examined under static conditions and adhesion to tumor necrosis factor‐alpha‐stimulated human umbilical vein endothelial cells was examined under flow conditions, using a parallel‐plate flow chamber. Results: PKCζ and Mac‐1 colocalized following stimulation with IL‐8. Blocking PKCζ prevented IL‐8‐induced Mac‐1 clustering while simultaneously increasing Mac‐1 affinity. To determine the relative contribution of affinity versus avidity in neutrophil adhesion, we examined adhesion under both static and flow conditions, and found that blocking PKCζ prevented neutrophil adhesion, despite increased affinity of Mac‐1. Conclusions: These data suggest that PKCζ is a negative regulator of Mac‐1 affinity and a positive regulator of Mac‐1 avidity. Further, Mac‐1 avidity is more important than increased affinity alone in regulating neutrophil firm adhesion.