Role of the Ly 1 antigen in interleukin 1‐induced thymocyte activation

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Abstract
Interleukin 1 (ILI), but not IL2-induced thymocyte proliferation was augmented by monoclonal antibodies (mAb) against the Ly 1 antigen. The anti-Ly 1 mAb could also co-stimulate thymocytes with phytohemagglutinin (PHA) alone, mimicking the effect of IL1. Moreover, overnight culture with PHA of thymocytes, but not of spleen T lymphocytes led to selectively enhanced expression of the Ly l antigen on the cell surface. Similar data were generated at the clonal level. Thus, a thymocyte hybridoma (22A6) could be stimulated to release IL2 in response to PHA plus IL 1, but also to PHA plus anti-Ly 1 mAb. In addition, 22A6 exhibited enhanced cell surface expression of the Ly l antigen after overnight culture with PHA. These data suggest a critical role for the Ly1 antigen in thymocyte proliferation, perhaps by serving as an IL 1-receptor.