Background:
The intestinal microbiome of men who have sex with men (MSM) is distinct as compared to non-MSM and is suggested to increase susceptibility to rectal HIV infection. Indeed, we recently demonstrated that dysbiosis-associated disruptions in host antimicrobial immunity increase susceptibility to rectal SIVmac239X in rhesus macaques (RMs; Macaca mulatta). Central to the susceptibility-associated antimicrobial network is DUOX2 – an epithelial sensor that catalyzes reactive oxygen species (ROS) production upon sensing pathobiont-derived uracil. We hypothesize that uracil bioavailability may increase susceptibility to rectal HIV.
Methods:
RMs were treated daily with (n=6) or without (n=8) oral uracil at 250 mg/m2. Blood, mesenteric lymph nodes (MLN), stool, and intestinal biopsies were taken before and 28 days into treatment. Animals were challenged intra-rectally with 4 TCID50 of SIVmac239X 56 days into treatment and every 2 weeks thereafter. We assessed immunity by flow cytometry and high throughput quantitative RT-PCR (NanoString) and the intestinal microbiome by 16S Illumina sequencing.
Results:
Oral uracil treatment reduced IFNγ, IL-17, IL-22, and TNFα expression by peripheral CD4+ and CD8+ T-cells. Isolated changes in cytokine expression were observed among MLN, jejunal, and rectal T-cells. Although uracil had limited effect on rectal T-cell function or transcript expression, we observed an increase in ROS production by rectal epithelial cells. Among the fecal microbiome, uracil-responsive taxa were largely restricted to Prevotellaceae, Lachnospiraceae, Lactobacillaceae, and Ruminococcaceae. No differences in time to infection or transmitter/founder variant acquisition were observed between control and treated RMs.
Conclusions:
Oral uracil treatment in RMs does not alter susceptibility to SIV acquisition. Although treatment induced significant shifts in peripheral T-cell function, these effects were not systemic, suggesting limited intestinal dissemination. Future studies which evaluate the effects of intestinal uracil on host immunity should consider alternate delivery methods.