REGULATED EXPRESSION AND FUNCTION OF CD11C/CD18 INTEGRIN ON HUMAN LYMPHOCYTES-B - RELATION BETWEEN ATTACHMENT TO FIBRINOGEN AND TRIGGERING OF PROLIFERATION THROUGH CD11C/CD18

CD11c/CD18 (p150,95) is a beta-2 integrin expressed by myeloid, natural killer and certain lymphoid cells such as some cytotoxic T cell clones and B cell malignancies. We have studied the expression and function of CD11c on resting and activated B lymphocytes. Flow cytometry, immunoprecipitation, and mRNA analyses showed that cell activation with phorbol esters or with a variety of stimuli such as Staphylococcus aureus or anti-mu-antibodies in combination with cytokines induced de novo CD11c/CD18 cell surface expression on most B cells while CD11b expression was not affected. Functional analysis of CD11c/CD18 on B cells revealed that it plays a dual role. First, CD11c/CD18 is implicated in B cell proliferation, as demonstrated by the ability of several anti-CD11c monoclonal antibodies to trigger comitogenic signals; and second, the newly expressed CD11c/CD18 mediates B cell binding to fibrinogen. Our data conclusively demonstrate the role of CD11c/CD18 on both B cell activation and adhesion processes.