The frequency of cells expressing perforin or granzyme B was significantly greater in CD38+ CD4+ T cells than in CD38- CD4+ T cells prior to and post infection (p = 0.001 and p = 0.011 prior to infection, and p = 0.012 and p = 0.017 at peak infection for perforin and granzyme B, respectively, Fig 3A and 3B). This evidence concerns the gene PRF1 and infection.