Abstract Body

Background: The gut mucosa is a major site of HIV-1-associated pathogenesis. Dendritic cells (DCs) play crucial roles in innate and adaptive immunity, in gut homeostasis and in pathogen defense, but the impact of HIV-1 infection on gut DCs has not been extensively studied. We investigated the impact of chronic, untreated HIV-1 infection on colon DC frequency and activation and evaluated associations with virological and immunological parameters. Methodology: Colonic mucosal cells (CMC) and peripheral blood (PB) mononuclear cells were obtained from 24 untreated HIV-1 infected (HIV-1+; median viral load (VL): 51,350 HIV-1 RNA copies/ml; median CD4 T cell count: 445 cells/μl) and 14 uninfected (HIV-1neg) subjects. Participants gave informed consent. Flow cytometry was used to determine frequencies (number per gram of mucosal tissue) of colon CD11chi HLA-DR+ myeloid DC (mDC) subsets (CD1c+ and CD1cneg) and CD303+ plasmacytoid DCs (pDC), DC maturation (% CD83+) and activation (CD40 MFI) state, and colon and PB CD4 and CD8 T cell activation (HLA-DR+CD38+). Cytokine production in cultured (16hrs) CMC was assessed using a multiplex assay. Mucosal HIV-1 VL was quantified by real time PCR. Non-parametric statistical tests were used for all analyses. Results: HIV-1+ and HIV-1neg donors had similar numbers of CD1c+ and CD1cneg mDCs and pDCs. However, HIV-1+ donors had a lower fraction of CD83+CD1c+ (p=0.02) and CD1cneg (p=0.001) mDCs in conjunction with increased levels of CD40 on CD1c+ (p=0.006) and CD1cneg (p=0.005) mDCs. The fraction of CD83+ pDCs were also reduced (p=0.03), but levels of CD40 on pDCs were similar to HIV-1neg donors. In HIV-1+ donors, CD40 expression on CD1c+ mDCs correlated with mucosal VL (r=0.49, p=0.04), with the number of activated colon CD4 (r=0.70, p=0.0009) and CD8 (r=0.59, p=0.008) T cells, with CMC production of pro-inflammatory IL-1β (r=0.72, p=0.003), IL-23 (r=0.67, p=0.008), IL-6 (r=0.68, p=0.006), TNF-α (r=0.66, p=0.009) and regulatory IL-10 (r=0.54, p=0.04), and with the percent of activated PB CD4 (r=0.61, p=0.006) and CD8 (r=0.53, p=0.02) T cells. No associations between activated DCs and PB CD4 count or plasma VL were observed. Conclusions: Untreated, chronic HIV-1 infection results in a dysregulated colon mDC phenotype characterized by a lower percentage of CD83+ mDCs, but increased expression of CD40. Increased CD1c+ mDC activation was associated with local T cell activation, higher mucosal HIV-1 viral load, and with mucosal cytokine production. Further, CD1c+ mDC activation was associated with higher levels of systemic T cell activation, thereby linking colon mDC activation to a marker of HIV-1 disease progression. Taken together, these findings suggest gut mDCs likely contribute to mucosal inflammation and HIV-1 pathogenesis.