A cytotoxic monoclonal antibody detecting a novel B cell membrane antigen expressed predominantly on cells bearing surface membrane immunoglobulin.

A new human B lymphocyte membrane antigen, CB2, has been detected by a mouse monoclonal IgM antibody. CB2 appears to be predominantly expressed on normal and malignant cells expressing surface membrane immunoglobulin (SmIg). By indirect immunofluorescence, the number of CB2-positive cells in normal peripheral blood correlated well with the number of SmIg-positive cells. Cytotoxicity studies on isolated cell populations showed that CB2 was present on normal B cells isolated from the spleens of 52 donors and on peripheral blood B cells from 8 donors. Monocytes, T cells, granulocytes, platelets, and red cells were CB2 negative. Only malignant cells expressing SmIg were positive. These included B-CLL, B lymphoma, prolymphocytic leukemia, and B lymphoma cell lines Daudi, Raji, and Conception. SmIg-negative leukemia cells, such as common acute lymphoblastic leukemia, acute and chronic myelogenous leukemia, and T cell leukemias, were negative. Blocking studies with human immunoglobulin suggests that the CB2 antigen is not directed against immunoglobulin determinants. Immunoperoxidase studies on normal lymph node sections show that CB2-positive cells are predominantly present in the mantle region of the follicle, whereas B1-positive cells are mainly in the germinal center.