Oligospecificity of the cellular adhesion receptor Mac-1 encompasses an inducible recognition specificity for fibrinogen

Mitogenesis, cellular aggregation, and motility follow upon the interaction of fibrinogen with certain defined cell surface receptors. In addition to circulating platelets and vascular endothelium, monocytes express what appears to be a receptor for fibrinogen. Evidence is presented here that the leukocyte adhesion receptor Mac-1 can be specifically induced to bind fibrinogen with characteristics immunochemically and functionally distinct from the established Arg-Gly-Asp-directed fibrinogen receptors. The competence of Mac-1 as a fibrinogen receptor is a general property of cells of monocyte and myeloid lineage acquired after maturational changes of some regions of the alpha subunit of Mac-1 during the process of cell differentiation. This ligand recognition specificity of Mac-1 is lacking for the resting cell. Rather, induction of fibrinogen binding capacity of Mac-1 is due to a cellular response to selected agonists characterized by inducing rapid transients of cytosolic Ca2+. Although different in activation pathways and recognition specificity, Mac-1 exhibits an oligospecific ligand versatility characteristic of other homologous Arg-Gly-Asp-directed adhesion receptors.