CD4 T cell subsets in the mucosa are CD28+Ki‐67−HLA‐DR−CD69+ but show differential infection based on α4β7 receptor expression during acute SIV infection

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Abstract
Background  CD4 T cell depletion in the mucosa has been well documented during acute HIV and SIV infections. The demonstration the HIV/SIVcan use the α4β7 receptor for viral entry suggests that these viruses selectively target CD4 T cells in the mucosa that express high levels of α4β7 receptor.Methods  Mucosal samples obtained from SIV infected rhesus macaques during the early phase of infection were used for immunophenotypic analysis. CD4 T cell subsets were sorted based on the expression of β7 and CD95 to quantify the level of SIV infection in different subsets of CD4 T cells. Changes in IL‐17, IL‐21, IL‐23 and TGFβ mRNA expression was determined using Taqman PCR.Results  CD4 T cells in the mucosa were found to harbor two major population of cells; ‐25% of CD4 T cells expressed the α4+β7hi phenotype, whereas the rest of the 75% expressed an α4+β7int phenotype. Both the subsets were predominantly CD28+Ki‐67‐HLA‐DR‐ but CD69+, and expressed detectable levels of CCR5 on their surface. Interestingly, however, α4+β7hiCD4 T cells were found to harbor more SIV than the α4+β7int subsets at day 10 pi. Early infection was associated with a dramatic increase in the expression of IL‐17, and IL‐17 promoting cytokines IL‐21, IL‐23, and TGFβ that stayed high even after the loss of mucosal CD4 T cells.Conclusions  Our results suggest that the differential expression of the α4β7 receptor contributes to the differences in the extent of infection in CD4 T cell subsets in the mucosa. Early infection is associated dysregulation of the IL‐17 network in mucosal tissues involves other non‐Th‐17 cells that likely contributes to the pro‐inflammatory environment in the mucosa during acute stages of SIV infection.

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