THE 175-ANTIGEN EXPRESSED ON MYELOID AND ERYTHROID-CELLS DURING DIFFERENTIATION IS ASSOCIATED WITH SERINE-PROTEASE ACTIVITY

Monoclonal antibody 175 recognizes a cell-surface antigen on more than 80% of nucleated ovine bone marrow cells (BMC). The distribution is u nusual, as the majority of differentiated myeloid and erythroid cells express the antigen (175 antigen), whereas mast cells, basophils, and the majority of lymphocytes do not. The level of 175 antigen expressio n has been shown to increase as BMC differentiate during hematopoiesis . Previous attempts to identify the 175 antigen have been unsuccessful . In this study, the 175 antigen was affinity-purified and shown to co ntain serine protease activity. Immunoblot analysis following sodium d odecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) of bone ma rrow cell lysates run under reducing or nonreducing conditions showed two closely adjacent protein bands (a doublet) of 28 to 30 kD molecula r weight. N-linked deglycosylation showed that the 30-kD band was a gl ycosylated form of the 28-kD protein. Both protein bands shared the sa me N-terminal amino acid sequence over 20 residues, with high homology with serine proteases. Affinity-purified 175 antigen was proteolytic in substrate gels, the activity being inhibited by the 175 monoclonal antibody (Mab) and the serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF), but not by metallo, thiol, or acid protease-specific inhibitors. The 175 antigen is therefore part of a growing family of c ell-surface proteases associated with hematopoietic cell differentiati on. (C) 1995 by The American Society of Hematology.