Immunological non-responders (INR) have increased non-AIDS morbidity. A proposed mechanism for INR’s inferior prognosis is microbial translocation across gut mucosa, which promotes chronic immune activation. In-depth immune function in gut mucosa of INR has not been systematically assessed, nor have the effects of probiotics.
In a cross-sectional study, we included three groups of Caucasian age-matched men: 20 INR (ART>4 years with HIV RNA <50 copies/ml and CD4 count <400 cells/µL for >3.5 years); 20 immunological responders (IR) (ART>4 years with HIV RNA <50 copies/mL and CD4 count >600 cells/µL for >3.5 years) matched on nadir CD4 count; and 20 HIV-negative controls. Mucosal biopsies from the terminal ileum and the sigmoid colon, fecal samples and blood were collected. INR received probiotics (>1.2*1010 cfu/day with five mixed probiotic strains) for 8 weeks in an open-label phase II exploratory interventional trial (NCT02640625), followed by an end-of-study colonoscopy. Lamina propria mononuclear cells were isolated and after mitogenic stimulation, frequencies of Th17 (CD4+IL-17+), Th22 (CD4+IL-22+) and Th1 (CD4+IFNγ+) were measured by flow cytometry. Soluble CD14, IL-6, CD163, CRP, Zonulin, IL-18, intestinal fatty acid binding protein (iFABP), lipopolysaccharide binding protein (LBP), LPS and CD25 were analyzed by ELISA. The microbiome was characterized by 16S rRNA gene sequencing (V3-V4).
INR had increased serum levels of iFABP and sCD14 compared with controls (p<0.05). The frequencies of gut mucosal Th17 and Th22 were not significantly different between the three groups. After stratifying INR and IR according to blood CD4/CD8 T cell ratio, INR with low (<0.5) CD4/CD8-ratio had significantly higher frequencies of gut mucosal Th17, Th22 and Th1 cells than IR with high (>1.0) CD4/CD8 T cell ratio (p<0.01). In INR, probiotics for 8 weeks significantly reduced the frequency of Th22 cells in terminal ileum (p<0.05), with a corresponding increase in mucosa-adherent bacterial diversity (Shannon Diversity Index, p<0.01 and Phylogenetic Diversity, p<0.05), whereas no significant changes were observed for the soluble markers.
INR had increased markers of impaired mucosal barrier function. INR with low blood CD4/CD8 T cell ratio had elevated frequencies of mucosal CD4 subsets, indicating a more pro-inflammatory tissue environment. The alterations were partially reversed by probiotics, providing a rationale for further trials of gut targeted treatment in INR.