We have previously described the derivation of a monoclonal antibody, S2C6, to a novel 50 Kdalton antigen associated with human urinary bladder carcinoma. No reactions were obtained with carcinomas of unrelated origin or with normal urothelial cells. However, the antibody also reacted with a similar antigen on some cell lines of B lymphocyte origin. Using large panels of target cells we have now shown that this reactivity was entirely restricted to cells of the B lineage within the haematopoietic system. As opposed to its apparent restriction to malignant cells of the urothelium, the S2C6 antigen was expressed by normal B lymphocytes as well as by many malignant B cells (chronic lymphocytic leukaemia, hairy cell leukaemia and immunocytoma). Pre-B cells derived from acute lymphocytic leukaemia and plasma cells from multiple myeloma lacked the antigen. Expression was significantly enhanced on cultured B cells from Burkitt lymphomas and on Epstein-Barr virus-transformed lymphoblastoid cell lines including those of the pre-B phenotype derived from fetal bone marrow. As judged from the molecular size and the distribution pattern displayed by the S2C6 antigen it appears to be distinct from other B cell antigens previously described. A possible relation of the S2C6 antigen to a receptor for B cell growth factors is discussed.

؊1 . Further, the entropy change (⌬S) at 25°C is large and negative. Far-and near-UV circular dichroism measurements display significant changes over the entire wavelength range upon binding of IGF-I to IGF-I R -Z. These data are all consistent with a significant change in structure of the system upon IGF-I binding.

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Paulie et al., 1984) and further delineate the heterogeneity of tumour-associated antigens in this human tumour system.