HIV infection and depletion of CD4 T helper (Th) cells in gut mucosal tissue are associated with microbial translocation and inflammation. We previously reported more significant depletion of Th17 than Th1 subsets in colon tissue in untreated HIV infection. Altered gut-homing by blood Th cells may be a contributing factor to overall gut Th cell depletion. Here, we investigated the gut-homing potential, activation and exhaustion states of peripheral blood CCR6+ Th17 and CXCR3+ Th1 cells and determined the colonic gene expression of specific chemokines that drive gut Th17 and Th1 homing (CCR6:CCL20; CXCR3:CXCL10).
Stored PBMC and colon biopsies from 16 untreated, chronic HIV-1-infected study participants (HIV+; median plasma viral load: 66,600 HIV-1 RNA/ml; median CD4 count: 410 cells/μl) and 13 uninfected controls (HIV-) from our previous clinical study (PMID: 24399150) were analyzed with consent. Flow cytometry was used to measure α4+β7+ (gut-homing), CD38+HLA-DR+ (activation) and PD1 expression (exhaustion) of blood CCR6+CCR4+CXCR3- (Th17) and CCR6-CCR4-CXCR3+ (Th1) memory (CD45RA-) CD4 T cells. CCL20 and CXCL10 transcript levels were evaluated in colon tissue by RNAseq. Measures of microbial translocation (plasma bacterial LPS and LTA) were performed as part of our previous study. Non-parametric tests were undertaken.
Expression of α4+β7+ was higher on Th17 (p=0.01) and lower on Th1 (P=0.03) cells in HIV+ persons compared to HIV- persons. Colonic gene expression of CXCL10 was significantly higher (P=0.01) and CCL20 trended lower (P=0.1) in HIV+ versus HIV- persons. Expression of CD38+HLA-DR+ and PD1 were significantly higher on Th17 and Th1 cells in HIV+ persons (all P<0.0001). Th17 activation and exhaustion expression inversely correlated with CD4 count (R=-0.68, P=0.005; R=-0.58, P=0.02 respectively), whereas Th1 activation and exhaustion did not. Exhausted Th17 positively correlated with LPS (R=0.59, P=0.02) and LTA (R=0.64, P=0.01) and exhausted Th1 with LTA (R=0.63, P=0.01).
Gut-homing profiles were altered on blood Th17 and Th1 cells during untreated HIV-1 infection and may result from dysregulated colonic tissue expression of chemokines necessary for their homing. Blood Th17 and Th1 cells displayed features of increased activation and exhaustion that associated with indicators of disease progression and microbial translocation.