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Nineteen different radiation-induced thymomas originating in BALB/c, NZB and NZW mouse strains were tested for Ig synthesis by short-term culture with 14C-amino acids followed by radioimmunoelectrophoresis. Twelve were negative, six produced light (L) chains and one synthesized a protein similar to IgM. The IgM producer, WEHI-22, and one of the L chain producers, WEHI-105, were established as cloned cultured cell lines and shown to possess the lymphoid cell characteristics of susceptibility to inhibition by low concentrations of thymidine and of cortisol. Both were also shown to bear the θ antigen, a thymus-derived (T) lymphocyte marker. Cells of the WEHI-22 line also possessed surface immunoglobulin readily detectable by binding of labeled anti-Ig antibody and were able to bind mouse antibody-coated sheep erythrocytes forming rosettes, while WEHI-105 did neither. The specificity of the Ig receptor mediating rosette formation appeared from myeloma protein competition experiments to be very similar to that of the receptor described for non-thymus-derived (B) cells. It was considered that WEHI-22 cells either possess a mixture of T and B cell characteristics or are neoplastic variants of T cells possessing surface IgM with antiglobulin activity.

Summary Pretreatment of normal adult mouse spleen cells, or peritoneal exudate cells from mice sensitized to DNP~CSA, with anti-immunoglobulin light polypeptide chain sera considerably suppressed the ability of these cells to induce the graft v8 host reaction or the transfer of delayed hypersensitivity. Anti-heavy chain sera did not cause this suppression. These results indicate that the antigen recognition site on lymphocytes involves an immunoglobulin light chain which is either free or bound to a new heavy chain type.