Monoclonal antibody NU-B1 reacts with novel human B-cell antigen distinct from known CD molecules

With the objective of determining whether monoclonal antibody NU-B1, which is restricted to the B-cell lineage since it has an undefined CD nomenclature, recognizes a novel antigen or not, we undertook the following studies. NU-B1 showed two clear bands at 50 kDa and 42 kDa under reducing or nonreducing conditions. NU-B1 positive cells in the lymph node were localized in the mantle and marginal zones. When a panel of hematopoietic cell lines was used expression of the NU-B1 was highly restricted to the B-cell lineage which is however, quite distinct from CD79b which shows identical reactivity when used to stain lymphoid tissue. Twelve B-cell precursor cell lines were NU-B1 positive but CD79b negative. CD79b showed dramatic down modulation by anti-IgM treatment. NU-B1 also showed down modulation; however it was weaker than that of CD79b. NU-B1 reacted with about 7.7% of peripheral blood mononuclear cells while NU-B1 did not react with neutrophils, monocytes, platelets, red blood cells. Two color staining using tonsillar cells demonstrated that NU-B1 positive cells coexpressed CD20. In a clinical study, NU-B1 reacted with all 43 cases of ALL including common ALL and biphenotypic leukemia, all 4 B-cell ALL, 2/4 B-cell CLL and 6/7 B-cell type malignant lymphoma. NU-B1 did not react with multiple myeloma, T-cell or myeloid leukemia/lymphoma. We conclude that mAb 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 leukemia/lymphoma.