CD4 T cell subsets in the mucosa are CD28+Ki-67-HLA-DR-CD69+ but show differential infection based on alpha4beta7 receptor expression during acute SIV infection

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 alpha4beta7 receptor for viral entry suggests that these viruses selectively target CD4 T cells in the mucosa that express high levels of alpha4beta7 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 beta7 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 TGFbeta 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 alpha4(+)beta7(hi) phenotype, whereas the rest of the 75% expressed an alpha4(+)beta7(int) phenotype. Both the subsets were predominantly CD28(+)Ki-67(-)HLA-DR(-) but CD69(+), and expressed detectable levels of CCR5 on their surface. Interestingly, however, alpha4(+)beta7(hi)CD4 T cells were found to harbor more SIV than the alpha4(+)beta7(int) 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 TGFbeta that stayed high even after the loss of mucosal CD4 T cells.

Conclusions: Our results suggest that the differential expression of the alpha4beta7 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.

Figure 1. Mucosal tissues harbor α4⁺β7^hi and α4⁺β7^intCD4 T cell subsets

(a) Representative dotplots showing that two major subsets can be delineated in the mucosa based on α4β7 expression. (b) Proportions of α4⁺β7^hi and α4⁺β7^intCD4⁺ T cell subsets in the mucosa. (c) Representative dotplots and (d) dynamics of CD4 T cells showing that most mucosal CD4 T cells are destroyed by day 14-17 pi. (e) α4⁺β7^hiCD4 T cells harbor more SIV DNA as compared to α4⁺β7^intCD4 T cell subsets. (f) Most α4⁺β7^hi and α4⁺β7^intCD4 T cell subsets express detectable levels of CCR5 on their surface. (g) Majority of the both α4⁺β7^hi and α4⁺β7^intCD4 T cell subsets are CD28⁺.

Figure 2. Mucosal CD4 T cells are Ki-67⁻HLA-DR⁻CD69⁺

(a) Representative dotplots showing that most of the α4⁺β7^hi and α4⁺β7^intCD4 T cell subsets are Ki-67⁻HLA-DR⁻ CD69⁺ prior to and after SIV infection. (b) Relative expression of IL-17, IL-21, IL-23, and TGFβ in total mucosal cells at day 7-10 and 14-17 pi.