Characterization of IL-17-producing T helper cells-like autoreactive T cells in aged mice

IL-17-producing T helper cells (Th17) are attracting attention as a new CD4-positive subset of T cells, reported to be responsible for various autoimmune diseases through stimulation of the release of inflammatory cytokines from target cells. However, most investigations of Th17 mediation of autoimmune diseases have focused on the experimental autoimmune models derived from young animals, with few studies that have analyzed physiological factors such as aging. The present study analyzed autoreactive T cells established in a syngeneic mixed lymphocyte culture (sMLC) from aged mice and examined their similarity with Th17. IL-17-producing autoreactive CD4-intermediate T cells were observed in the sMLC; these expressed several stem cell markers or an immunosuppressive receptor PD-1 on the cell surface and so seemed to be different to typical Th17 cells. RT-PCR analysis revealed that purified Th17-like cells also expressed Il17a, Il17f, Il23r, Rorc and Tdt mRNA, but not Rag1 or Rag2 mRNA. These findings that it is likely that Th17-like cells are involved in autoimmune responses in aged mice.