CD4+ T-cell subsets and cytokines involved in peripheral tolerance.

Peripheral tolerance is induced under conditions that avoid activation of antigen-presenting cells (APCs) to release cytokines. Such tolerance occurs in both CD4+ T helper (Th)-cell subsets (Th1 and Th2), probably because it is induced in precursor cells. By contrast, activation of APCs to release cytokines by immunization or infection activates either both subsets or predominantly one of them. A model for CD4+ T-cell tolerization and subset expansion is presented here.