A Unique Human B Lymphocyte Antigen Defined by a Monoclonal Antibody

We produced a hybridoma designated 4G7 from a mouse immunized with chronic lymphocytic leukemia cells. The 4G7 hybridoma secretes an IgG1 antibody that is specific for normal and malignant B lymphocytes. Using dual color immunofluorescence staining, this antibody reacted with all immunoglobulin-positive cells but no T cells in normal peripheral blood. There was no detectable 4G7 antigen on monocytes, platelets, red cells, granulocytes, or phytohemagglutinin-activated T cells. When PBL were depleted of 4G7 positive cells and stimulated with pokeweed mitogen, secreted immunoglobulin levels fell to less than 10% of control values on Day 5 and less than 1% of control on Day 7. This antibody was reactive with 155 of 176 B lineage neoplasms on which it was screened. Thirty-five cases of myeloid or T-lymphoid malignancy were negative. Our studies show that the 4G7 antigen modulates in the presence of excess antibody. Free 4G7 antigen was not found circulating in human serum. The cell surface antigen identified by 4G7 was sensitive to pronase proteolysis but resistant to trypsin and chymotrypsin digestion. A comparison of 4G7 with other known B-cell antibodies indicates that the 4G7 antigen has not been previously identified. This antibody is of use for the identification of normal B lymphocytes, the study of B-cell differentiation, and the characterization of lymphoid malignancies.