Th17 cells are not preferentially lost from the GI tracts of SIV-infected SMs. GI tract lymphocytes from cohorts of SIV-infected (●) and uninfected sooty mangabeys (○) were stimulated with PMA and ionomycin for 4 hours in the presence of brefeldin A and stained as in “Intracellular cytokine assay.” Frequencies of GI tract memory CD4 T cells that produce either IL-17 (A) or IFN-γ (B) were then measured by flow cytometry. (C) Expression of IL-23R by memory CD4 T cells in the GI tracts of SIV-infected (●) and SIV-uninfected sooty mangabeys (○). (D) Frequencies of PB memory T cells that produce IL-17 from SIV-infected (●) and uninfected (○) sooty mangabeys.