Expression of the immunoglobulin-associated protein B29 in B cell disorders with the monoclonal antibody SN8 (CD79b)

We studied the expression of the immunoglobulin-associated membrane protein B29 in 499 cases of chronic B cell diseases using the monoclonal antibody SN8 (CD79b). SN8 was positive in 5% (17/330) of chronic lymphocytic leukemia (CLL) and 100% (15/15) of B prolymphocytic leukemia. The expression of B29 in other B cell disorders was, as a rule, significantly higher than in CLL. Two thirds of non-Hodgkin's lymphomas in leukemic phase were SN8 positive, including lymphoplasmacytic (45%), follicular (83%), mantle cell (92%) and splenic lymphoma with villous lymphocytes (74%) while only 25% of hairy cell leukemias were SN8 positive. Within CLL, 2.3% of typical cases were SN8+ while 16% of cases with atypical morphology and an increased number of prolymphocytes were SN8+. Our results suggest a useful role for SN8 in the immunophenotypic differentiation of B cell disorders as a marker for non-CLL diseases. The analysis of B29 expression may throw light into the structure of the B cell antigen receptor in B cell malignancies while the distinctive reactivity profile of SN8 has direct applications to diagnosis.