Identification of a high molecular weight protein on the surface of murine thymus and thymus-dependent cells.

Rabbit anti-mouse Ig reacted with mouse thymocytes resulting in the formation of caps which were shed into the medium and subsequently injected into rabbits. The antiserum from these animals (AMTP) reacted strongly with thymocytes and peripheral T cells and weakly with B cells. The antiserum did not react via the Thy-1 antigen and could be made specific for T lymphocytes by absorption with B lymphocytes. By surface labeling of lymphocytes with 125I, it could be shown that the major T lymphocyte antigen recognized by AMTP was one, or possibly two, large, single chain molecules with a molecular weight of approximately 200000. This molecule was not Ig and, furthermore, the AMTP did not react with cell surface Ig of B lymphocytes. The implications of this finding for previous reports on the existence of immunoglobulin on T lymphocytes are discussed.