THE BETA-2 INTEGRIN MAC-1 BUT NOT P150,95 ASSOCIATES WITH FC-GAMMA-RIIA

In this study we have compared the ligand binding activity of the two closely related beta 2 integrins, Mac-1 and p150,95, which are express ed separately as receptors permanently transfected into K562 cells. Ma c-1 has previously been shown to associate with Fc gamma R, particular ly Fc gamma RIII, but K562 cells express only endogenous Fc gamma RIIA . We have, therefore, taken advantage of this situation to examine a p ossible relationship between Fc gamma RIIA with Mac-1 and p150,95 in t he absence of other Fc gamma R. The main finding is that anti-Fc gamma RII mAb have a profound inhibitory effect on cell adhesion mediated b y Mac-1. but not on the adhesion mediated by p150,95. Thus, in spite o f the fact that Mac-1 and p150,95 bind to the same or at least a very similar selection of ligands, their association with other receptors o n the cellular membrane. and therefore their mode of regulation may be different.