['The objective of this study was to examine the role of protein kinase C zeta (PKCzeta) in interleukin (IL)-8-mediated activation of Mac-1 (CD11b/CD18) in human neutrophils.', 'Neutrophils were stimulated with IL-8 in the presence or absence of pharmacologic inhibitors of PKC or a myristoylated PKCzeta 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 PKCzeta was also probed using IE 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', 'PKCzeta and Mac-1 colocalized following stimulation with IL-8. Blocking PKCzeta 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 PKCzeta prevented neutrophil adhesion, despite increased affinity of Mac-1.'] Does the atypical zeta ( zeta ) isoform of protein kinase C regulate CD11b/CD18 activation in human neutrophils?