Differences in the expression of a cell surface antigen among various murine myeloma tumor cells

Some, though not all, murine myeloma tumors either lack an antigen (B1) present in normal B lymphocytes, or have a low level of this antigen. Rabbit antiserum against BALB/c thymus absorbed with brain and MPC 11 myeloma cells (RAT 1) was cytotoxic in the presence of complement to all types of normal lymphoid cells, but not to MPC 11 cells. RAT 1 inhibited the formation of direct and indirect plaque forming cells and rosette forming cells. This inhibitory effect could be abolished by absorption of RAT 1 with normal bone marrow cells. Quantitative absorption experiments showed that MPC 11 cells represented not more than 10% of the amount of B1 antigen present in spleen cells. The B1 antigen was present in the plaque forming cells of BALB/c, DBA/2, A/J and C57BL/6 mice, but absent from those of C3H, SJL/J and AKR/J mice. The B1 antigen could, therefore, be H 2 linked, or identical with H 2 determinants 27, 28 and 29. The pattern of sensitivity of the various myelomas to the cytotoxicity of anti H 2 serum was, however, different from that of RAT 1. In addition, absorption of various anti H 2 sera with MPC 11 myeloma cells indicated that the antigen lacking in myeloma cells is probably not a direct constituent of the H 2 antigen complex. The finding that the level of the B1 antigen was reduced only in some myelomas, but not in others, indicated that the loss of this antigen was not an obligatory event in the neoplastic transformation of B lymphocytes.