Enrichment for Th1 Cells in the Mel-14+ CD4+ T Cell Fraction in Aged Mice

CD4+ T cells from young and aged mice were sorted into Mel-14+ cells which are regarded as naive cells and Mel-14- cells which are regarded as memory cells. These subsets were stimulated in short-time cultures with anti-CD3 or anti-CD3/anti-CD28 in order to determine the presence of Th1 and/or Th2 cytokines. Based on the simultaneous production of IL-2, IL-4, IL-10, and IFN-γ upon anti-CD3 stimulation by Mel-14- cells from young and aged mice, it is concluded that this cell population comprises Th1, Th2, and/or Th0 cells. Mel-14+ cells from young mice only secrete substantial amounts of IL-2 in the presence of anti-CD28 as a costimulatory signal and can therefore be regarded as Th precursor cells. By contrast, Mel-14+ cells from aged mice responded to anti-CD3 alone, not only by the production of IL-2 but also by the production of high amounts of IFN-γ and minute amounts of IL-4 and IL-10, suggesting that these "naive" cells in aged mice are enriched for Th1 cells. This was not due to lack of CD28 triggering since anti-CD28 enhanced IFN-γ as well as IL-4 and IL-10 to a similar extent. Our data therefore indicate that Mel-14 is not exclusively expressed on naive CD4+ T cells.