p150,95, the third member of the Mac-1, LFA-1 human leukocyte adhesion glycoprotein family

Abstract

Monoclonal antibodies specific for p150,95, a third member of the Mac-1 and lymphocyte function-associated antigen-1 (LFA-1) leukocyte adhesion protein family, have been identified and used to study the biochemistry and cellular expression of p150,95. p150,95 is a noncovalently associated heterodimer containing alpha X and beta subunits of Mr = 150,000 and 95,000 respectively. Findings suggest that the p150,95 alpha X beta complex shares a common beta subunit with the alpha L beta LFA-1 and alpha M beta Mac-1 complexes. Co-precipitation experiments demonstrated identity between the p150,95 molecule precipitated by anti-beta MAb and by p150,95-specific MAb. Patients with a previously demonstrated genetic deficiency in Mac-1 and LFA-1 fail to express p150,95. Deficiency of the Mac-1, LFA-1, and p150,95 alpha beta complexes on the surface of patient cells appears due to a defect in the common beta subunit. The lack of cross-reaction of p150,95-specific MAb with LFA-1 and Mac-1, which appear to utilize identical beta subunits, suggests that the determinant is specified by the alpha X rather than the beta subunit of p150,95. The data suggest that alpha X is yet a third member of a family of alpha subunit proteins that associate with a common beta subunit, are differentially regulated in leukocyte differentiation, and function in adhesion reactions. p150,95 is normally expressed on blood monocytes and granulocytes. Chemoattractants such as f-Met-Leu-Phe stimulate a rapid, fivefold increase in surface expression that is not dependent on protein synthesis and appears to reflect mobilization of an intracellular latent pool. The intimate relation between the lack of chemoattractant-stimulated upregulation of p150,95 and Mac-1 by patient granulocytes and their failure to upregulate adhesiveness to these same stimuli in vitro, or to diapedese and migrate into inflammatory sites in vivo, is discussed.