B lymphocyte/carcinoma antigen (BLCa): functional study in B cells.

BLCa is an antigen expressed on the surface of B lymphocytes and certain carcinomas. In this study we have demonstrated that BLCa is distinct from known B cell antigens classified by 'clusters of differentiation' (CD). In particular, the monoclonal antibody MA6, which identifies BLCa, can be distinguished from antibodies of the CDw40 group, which detect an antigen of similar molecular weight expressed also on B cells and certain carcinomas. The expression of BLCa on B cells was measured as tonsil B cells were activated (by anti-Ig and interleukin-4 (IL-4)), induced to proliferate (by low molecular weight B Cell Growth Factor (LMW-BCGF), and induced to differentiate (by B Cell Differentiation Factor, BCDF). Expression of BLCa increased in response to LMW-BCGF. The effect of inclusion of MA6 antibody in cultures with the B cell stimuli was also investigated. MA6 showed an anti-proliferative effect which was antibody-dose dependent, but did not otherwise inhibit or co-operate with anti-Ig. IL-4, LMW-BCGF or BCDF.