Transient inhibition of interleukin 4 signaling by T cell receptor ligation

Interleukin (IL)-4 and IL-12 together with T cell receptor (TCR) engagement are crucial for the differentiation of CD4+ T cells into T helper (Th)2 or Th1 cells, respectively. Although IL-4 receptors (IL-4Rs) but not IL-12Rs are expressed on naive CD4(+) T cells, IL-4 has no apparent advantage over IL-12 in driving naive T cell differentiation when the cells are primed wit h both IL-4 and IL-12 in vitro. It was found that IL-4-induced phosphorylat ion of Janus kinases 1 and 3, IL-4R alpha, signal transducer and activator of transcription 6, and insulin receptor substrate 2 was strikingly but tra nsiently inhibited by TCR Ligation both in conventional and TCR transgenic T cells, TCR engagement also blocked the expression of an IL-4-inducible ge ne. Signals induced by other cytokines, including IL-e, IL-6, and interfero n alpha, but not by insulin-like growth factor 1, were also blocked by TCR engagement. The capacity of various inhibitors to reverse TCR-mediated inhi bition of IL-4 signaling suggested that activation of the Ras-mitogen-activ ated protein kinase pathway and of the calcineurin pathway contribute to de sensitizing IL-4R. IL-4 responsiveness returned at about the time (similar to 12 h) that IL-12-mediated signaling was first observed. Thus, through di fferent mechanisms, neither IL-4R nor IL-12R has any clear advantage in pol arizing cells; rather, the availability of cytokine is probably the limitin g factor in this process.