Accessory cells precondition naïve T cells and regulatory T cells for cytokine-mediated proliferation

Abstract

Naïve Tcells and regulatory Tcells, when purified, do not proliferate to the γc-cytokines IL-2, IL-7, or IL-15, despite their expression of cognate cytokine receptors. Dendritic cells (DCs) enabled the Tcell proliferation to these cytokines, through cell-to-cell contact, but independent of Tcell receptor stimulation. This effect lasted after separation of Tcells from DCs, enabling enhanced proliferation of the Tcells in DC-depleted hosts. We propose calling this a "preconditioning effect". Interestingly, IL-2 alone was sufficient to induce phosphorylation and nuclear translocation of STAT5 in Tcells, but could not activate MAPK and AKT pathways and failed to induce transcription of IL-2 target genes. "Preconditioning" was necessary to activate these two pathways and induced weak Ca2+ mobilization independent of calcium release-activated channels. When preconditioning was combined with IL-2, full activation of downstream mTOR, 4E-BP1 hyperphosphorylation, and prolonged S6 phosphorylation occurred. Collectively, accessory cells provide Tcell preconditioning, a unique activation mechanism, controlling cytokine-mediated proliferation of Tcells.