Induction of Interleukin 2-Responsiveness in Thymocytes of the Transgenic Mice Carrying Ick -Transgene

The role of lek gene in T cell proliferation and differentiation was investigated with transgenic mice carrying human lek cDNA whose expression was regulated by the promoter of mouse H-2K^b and the enhancer element of mouse IgH. RNase protection assay revealed that the lek transgene was expressed in the thymus and spleen, whereas immunoblot analysis demonstrated that amounts of p56^/ck in freshly isolated lymphoid organs were almost equal between transgenic mice and negative littermates. Cell-surface marker analyses of the thymocytes and peripheral lymphocytes revealed no remarkable difference between both groups. Notable finding is that the thymocytes from transgenic mice showed a significant proliferative response to the stimulation with IL-2, but not the thymocytes from negative littermates. Further analysis revealed that CD4+8^- single positive thymocytes proliferated in response to IL-2. While surface expression levels of IL-2Ra and IL-2Rβ of these CD4+8^- thymocytes from transgenic and control mice were almost equal before stimulation with IL-2, the expression of IL-2Rβ was induced only in transgenic thymocytes after stimulation with IL-2. Immunoblot analysis demonstrated that the expression of p56^/ck of transgenic thymocytes was not down-reguated at 4 hr after stimulaion with IL-2, whereas p56^/ck of control ones were not detectable any more at 4 hr after stimulation with IL-2. Moreover, in vitro kinase assay substantiated such unchanged expression of p56^/cA in the thymocytes from transgenic mice: the kinase activities of p56^/ck did not decrease in thymocytes from transgenic mice after stimulation with IL-2, while kinase activities of control ones were significantly down-regulated by stimulation of IL-2. These results suggested that a significant proliferative response found in the thymocytes from β&-transgenic mice after the stimulation with IL-2 was caused by a constitutive expression of p56^/ck in these thymocytes even after the stimulation. Our findings, therefore, support a possibility that p56^/c6 may play a role in the IL-2R-mediated signaling system in CD4+8~ thymocytes.