title: Uncoupling of IL-2 signaling from cell cycle progression in naive CD4+ T cells by regulatory CD4+CD25+ T lymphocytes.
abstract: Prior reports have shown that CD4(+)CD25(+) regulatory T cells suppress naive T cell responses by inhibiting IL-2 production. In this report, using an Ag-specific TCR transgenic system, we show that naive T cells stimulated with cognate Ag in the presence of preactivated CD4(+)CD25(+) T cells also become refractory to the mitogenic effects of IL-2. T cells stimulated in the presence of regulatory T cells up-regulated high affinity IL-2R, but failed to produce IL-2, express cyclins or c-Myc, or exit G(0)-G(1). Exogenous IL-2 failed to break the mitotic block, demonstrating that the IL-2 production failure was not wholly responsible for the proliferation defect. This IL-2 unresponsiveness did not require the continuous presence of CD4(+)CD25(+) regulatory T cells. The majority of responder T cells reisolated after coculture with regulatory cells failed to proliferate in response to IL-2, but were not anergic and proliferated in response to Ag. The mitotic block was also dissociated from the antiapoptotic effects of IL-2, because IL-2 still promoted the survival of T cells that had been cocultured with CD4(+)CD25(+) T cells. IL-2-induced STAT5 phosphorylation in the cocultured responder cells was intact, implying that the effects of the regulatory cells were downstream of receptor activation. Our results therefore show that T cell activation in the presence of CD4(+)CD25(+) regulatory T cells can induce an alternative stimulation program characterized by up-regulation of high affinity IL-2R, but a failure to produce IL-2, and uncoupling of the mitogenic and antiapoptotic effects of IL-2.
authors.affiliation: Department of Pathology, St. Jude Children's Research Hospital, 332 North Lauderdale Street, Memphis, TN 38105, USA.
authors.forename: Christine T
authors.initials: CT
authors.lastname: Duthoit
authors.forename: Divya J
authors.initials: DJ
authors.lastname: Mekala
authors.forename: Rajshekkhar S
authors.initials: RS
authors.lastname: Alli
authors.forename: Terrence L
authors.initials: TL
authors.lastname: Geiger
mesh_terms: D000818:Animals; D015153:Blotting, Western; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D002453:Cell Cycle / Q000502:physiology*; D002478:Cells, Cultured; D018920:Coculture Techniques; D004268:DNA-Binding Proteins / Q000276:immunology; D005434:Flow Cytometry; D007376:Interleukin-2 / Q000276:immunology*; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D008822:Mice, Transgenic; D008894:Milk Proteins / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D015375:Receptors, Interleukin-2 / Q000276:immunology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D015534:Trans-Activators / Q000276:immunology
chemical_list: D004268:DNA-Binding Proteins; D007376:Interleukin-2; D008894:Milk Proteins; D011948:Receptors, Antigen, T-Cell; D015375:Receptors, Interleukin-2; D050799:STAT5 Transcription Factor; D015534:Trans-Activators