Monoclonal antibody NU-B1 reacts with novel antigen on human B cells in mantle and marginal zones distinct from known CD molecules

To analyze the cellular antigens of human B-cell lineage, a monoclonal antibody, NU-B1, was raised using the acute lymphoblastic leukemia (ALL) cell line NALM-16 as the immunogen. NU-B1 reacted with 7.7 ± 3.9% of the healthy adult peripheral blood mononuclear cells but not with neutrophils, monocytes, red blood cells or thymocytes. In order to distinguish the reaction specificity of NU-B1, two-color immunofluorescence staining using tonsillar cells was performed, and it was demonstrated that NU-B1-positive cells coexpressed CD20, which is a representative B-cell antigen. The expression of NU-B1 was highly restricted to cells of B-cell lineage when a panel of hematopoietic cell lines was examined. In a pathoimmunohistological study using human lymph node tissue, NU-B1-positive cells were localized in the mantle and marginal zones. In a clinical study, NU-B1 reacted specifically with leukemias/lymphomas of B-cell lineage: all 43 cases of ALL including common ALL and biphenotypic leukemia, all 4 cases of B-cell ALL, 6/7 B-cell type malignant lymphomas and 2/4 B-cell chronic lymphocytic leukemias. NU-B1 did not react with multiple myeloma, T-cell or myeloid leukemias/lymphomas. Immunoprecipitation of NU-B1 revealed two clear bands at 50 kDa and 42 kDa under either reducing or nonreducing conditions. Although anti-IgM treatment induced dramatic down modulation of CD79b, the NU-B1 antigen was also down modulated, but only slightly. However, crosslinking of NU-B1 did not induce tyrosine phosphorylation of intracellular proteins or the mobilization of calcium in NALM-16. The present results revealed that the antigenic determinant recognized by NU-B1 is not surface immunoglobulin chains, HLA-DR, a receptor for C3, Fc for immunoglobulin chains or any known CD molecule. We conclude that monoclonal antibody NU-B1 recognizes a novel human B-cell restricted antigen distinct from known CD molecules, and that it is a useful antibody in the immunophenotyping and classification of leukemias/lymphomas.