Differential activation of signal transducer and activator of transcription (STAT)3 and STAT5 and induction of suppressors of cytokine signalling in Th1 and Th2 cells

Cytokines direct the differentiation of naive CD4(+) T cells into either IFN-gamma-producing T(h)1 cells or IL-4-producing T(h)2 cells. In this study, we analyzed the activation of signal transducer and activator of transcription (STAT)1, STAT3 and STAT5 (together with STAT4 and STAT6), and the expression of the recently identified suppressor of cytokine signalling (SOCS) proteins, in differentiated T(h)1 and T(h)2 cells, both before and after re-stimulation with anti-CD3 and anti-CD28. In addition to the polarized activation of STAT4 in T(h)1 cells and STAT6 in T(h)2 cells, we found that STAT3 and STAT5 are selectively activated in T(h)1 cells after differentiation. This activation of STAT3 and STAT5 was maintained after TCR re-stimulation. The selective activation of STAT3 and STAT5 in T(h)1 cells was associated with differential induction of SOCS molecules. After restimulation, SOCS1 expression was significantly increased in T(h)2 cells, but not in T(h)1 and nonpolarized 'T-h' cells. Additionally, the level of CIS was higher in T(h)2 cells compared with T(h)1 and T-h cells. In contrast, the expression of SOCS3 was higher in T(h)1 cells. The differential induction of SOCS proteins was paralleled by the differential expression of cytokines in re-stimulated T(h)1 and T(h)2 cells (IFN-gamma and IL-4/IL-13 respectively). Our results suggests that STAT3 and STAT5, possibly regulated by the SOCS proteins, may play a role in the differentiation of T-h cells, and in the maintenance of the T(h)1 and T(h)2 phenotype.