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 r esting lymphocytes the antigen is induced rapidly within 2-4 h followi ng stimulation of the cells using mitogens or antibodies against the T -cell CD3 antigen and sIgM on B cells, respectively. Immunoprecipitati on and Western Blotting indicated that the MoAb recognizes a molecule in a range of 78-85 kDa. Beyond its activation-dependent expression on lymphocytes the antigen was detected also on myelo-monocytic cells. E xpression kinetics and cellular distribution of this molecule suggest that it is distinct from previously described activation-dependent cel l-surface antigens such as CD69, CD25 and 4F2.