Levels of blood and intestinal CD4⁺IL-21⁺ T cells in nonpathogenic SIV infection of SMs. The percentages (left panels) and absolute values (right panels) of circulating (A) and intestinal (B) CD4⁺IL-21⁺ T cells were compared between chronically, SIV-infected (○) and uninfected (●) SMs. In RBs, the absolute values of IL-21–producing CD4⁺ T cells are expressed as fraction of total CD3⁺ T cells (B). Statistical analyses were performed to compare the levels of CD4⁺IL-21⁺ T cells between SIV-infected and uninfected animals.