Infected animals that received BrdU on days 3 to 10 p.i. had splenocytes harvested, and the proportions of BrdU+ cells out of CD4+ T cells and their numbers were measured on day 60 p.i., when premunition is detectable, day 120 p.i., when it is not, and day 200 p.i., when protection from parasitemia has been shown to be detectably lost (11). This evidence concerns the gene CD4 and parasitic infectious disease.