CD63 ASSOCIATES WITH TYROSINE KINASE-ACTIVITY AND CD11 CD18, AND TRANSMITS AN ACTIVATION SIGNAL IN NEUTROPHILS/

As a member of the tetraspan family, it has been hypothesized that CD6 3 may be associated with signal transduction; however, its role in leu kocyte function is unknown, To examine the potential ability of CD63 t o activate neutrophils, the effects of five CD63 mAbs, AHN-16, -16.1, -16.2, -16.3, and -16.5, were examined for their ability to alter neut rophil adhesion to HUVEC monolayers. These CD63 Abs increased neutroph il adhesion to resting and TNF-stimulated HUVEC monolayers. This incre ase in neutrophil adhesion caused by CD63 Abs was blocked by a CD18 Ab and was associated with up-regulation of CD11/CD18 and down-regulatio n of CD62L on the neutrophil surface. CD11/CD18 was also found to be a ssociated with CD63. This increase in neutrophil adhesion required phy siologic extracellular calcium concentrations at or near the time of C D63 Ab binding, The incubation of CD63 Abs with cells in the absence o f calcium for 10 min before repletion of calcium resulted in no increa se in neutrophil adhesion, Protein kinase activity was detected in neu trophils associated with CD63, Most of the protein kinase activity ass ociated with these Ags was tyrosine kinase activity, with a lesser amo unt of threonine and serine kinase activities, Src family kinases Lyn and Hck accounted for much of the associated tyrosine kinase activity. The data suggest that CD63 Ab binding to the neutrophil surface trigg ers a transient activation signal that requires extracellular calcium and regulates the adhesive activity of CD11/CD18. Associated protein k inase activity may play a role in signal transduction by CD63 to regul ate other cell functions.