Characterization of an Early Activation-Dependent Antigen on Lymphocytes Defined by the Monoclonal Antibody BL-Ac(F2)

A novel activation-dependent lymphocyte cell-surface antigen which is recognized by a MoAb, BL Ac(F2), is described. Although not found on resting lymphocytes the antigen is induced rapidly wiihin 2–4 h following stimulation of the cells using mitogens or antibodies against the T-eell CD3 antigen and sIgM on B cells, respectively. Immunopreeipitation and Western Blotting indicated that the MoAb recognizes a molecule in a range of 78 85 kDa. Beyond its activalion-dependent expression on lymphocytes the antigen was detected also on myelo-monocytic cells. Expression kinetics and cellular distribution of this molecule suggest that it is distinct from previously described activation-dependent cell-surface antigens sueh as CD69, CD25 and 4F2.