AR was induced by allogeneic stimulation in both CD45RAand CD45RA+ subsets of CD4 and CD8 T cells at frequencies ranging from 0.028% to 0.35%. These levels were comparable to the frequencies of CD4+ CD45RA+ or CD45RA-T cells producing IL-2, or CD4+ CD45RA-memory T cells producing IFNc. As expected, IL-2 was produced by both memory (CD45RA-) and naive (CD45RA+) CD4 T cells, whereas IFNc (and IL-4 at low levels) were produced mainly by memory cells ( Figure 4B ).