DIFFERENCES IN THE EXPRESSION OF LY-6C ON NEUTROPHILS AND MONOCYTES FOLLOWING PI-PLC HYDROLYSIS AND CELLULAR ACTIVATION

All leukocytes, except some subsets of lymphocytes, express Ly-6C. However, virtually all of the regulation studies of this antigen have been done on lymphocytes only. Recently we showed that monocytes and neutrophils express 10-100 times the level of Ly-6C expressed by lymphoid cells. We compared Ly-6C expression on neutrophils and monocytes following short-term cell activation induced by C5a or phorbol esters or treatment with phosphatidylinositol-specific phospholipase-C (PI-PLC). Activation of the neutrophil led to a rapid (< 30 min) increase in surface expression of Ly-6C, but similar treatment had little effect on or slightly diminished the expression of the monocyte molecule. Prolonged treatment of the monocyte with IFN-gamma (24 h) led to increased Ly-6C expression. Low doses of TNF-alpha inhibited the up-regulation of Ly-6C induced by IFN-gamma. Similar to what has been described for the lymphocyte, the monocyte form of Ly-6C was hydrolyzed by PI-PLC treatment within 30 min. In contrast, the neutrophil molecule was unaffected by PI-PLC for up to 2 h. SDS-PAGE Western blot analysis demonstrated that the neutrophil and monocyte molecules were in the same molecular weight range (14-18 kDa Mr). Our results clearly show differences in the regulation of Ly-6C expression on monocytes versus neutrophils. Thus, it is likely that the potential function of Ly-6C will be unique for each cell.