Thy-1-negative and Ly-1-negative variants of T cells produce interleukin 2 in response to mitogens

IL 2 production by T cell variants, which lack the Thy-1 or Ly-1 surface glycoproteins, was studied. Cross-linking of the Thy-1 molecule resulted in IL 2 production by the EL4 thymoma and by a T cell hybridoma, suggested that Thy-1 may play a role in T lymphocyte triggering. To further study the functional role of this molecule, Thy-1-negative variants were selected and analyzed for IL 2 production in response to phorbol-12-myristate-13-acetate (PMA) or to Con A. It was demonstrated that in spite of their failure to express Thy-1, the Thy-1-negative clones were capable of IL 2 production. These results indicated that although Thy-1 cross-linking triggers cell activation, a signal provided by Thy-1 is not indispensable for cell activation by mitogens. The T cell tumor line LBRM331A5 responds synergistically to IL 1 and PHA by releasing IL 2. It was demonstrated by anti Ly-1 monoclonal antibodies and PHA co-stimulated LBRM331A5 cells, as did IL 1 plus PHA. Thus, anti Ly-1 antibodies mimic the effect of IL 1, suggesting a role for Ly-1 antigen in T cell activation, perhaps by serving as an IL 1 receptor or as an associated molecule. To further study the functional role of Ly-1 and its relation to IL 1 receptor, Ly-1-negative variants of the LBRM331A5 cell line were selected and analyzed for IL 2 production in response to PHA plus IL 1. It was demonstrated that the Ly-1-negative clones were capable of IL 2 production as efficiently as Ly-1-positive clones. These results indicate that Ly-1 and IL 1 receptor are distinct molecules, which are involved in different activation pathways.