Abstract Body

Background: We co-exist with an abundant microbiota that cooperate with and help regulate our immune system. However, during HIV infection the microbial community in the gut is altered to a distinctive composition which is not consistently restored to that of seronegative subjects by ART. Recently, our group illustrated that in contrast to uninfected patients, the microbial community in HIV infected subjects exhibits increased phylogenetic diversity and is Prevotella-rich and Bacteroides-poor. Here we seek to understand the impact of the change in gut microbiota on HIV infection by characterizing innate and adaptive immune responses, including T regulatory cells, to selected gut bacteria that changed with HIV infection. Methodology: Based on our 16S rRNA sequencing from HIV+ and HIV- subjects we chose four characteristic bacteria; Bacteroides dorei, Bacteroides fluxus, which were decreased, and Prevotellaceae copri, Erysipelotrichaceae biforme, which were elevated with HIV infection. PBMCs of 15 HIV-positive and 18 HIV-seronegative subjects were incubated with lysate of these bacteria. Levels of inflammatory cytokines were evaluated at 24 hours post inoculation by bead array assay, and T regulatory cells and CD4+ T cell proliferation were enumerated by flow cytometry at either 3 or 6 days. Statistical significance was determined using Mann-Whitney T tests. Results: HIV-infected subjects had significantly elevated levels of both TNF-α and IL-10 to all bacteria in comparison with HIV-seronegative (p<0.05). Levels of T regulatory cells also increased with all bacteria although levels were not significantly different in regard to HIV status. Median levels of T regulatory cells from PBMC cultured with B. fluxus (2.24%) and B. dorei (2.08%) were greater compared to that of P. copri (0.44%; p=0.03, p=0.05, respectively) and E. biforme (0.06%; p=0.02, p=0.03, respectively). All bacteria induced CD4+ T cell proliferation regardless of HIV status. However, with HIV infection CD4+ T cell proliferation to B. fluxus (1.30%) and B. dorei (0.47%) was reduced compared to HIV-seronegative subjects (4.77% and 1.78%; p=0.03, p=0.08, respectively), while responses to P. copri and E. biforme were not significantly different. Conclusions: These results illustrate that HIV infection is associated with a distinct microbial signature that is more pro-inflammatory. Furthermore, Bacteroides species which are lost during HIV infection are better adapted for inducing T regulatory cells than P. copri and E. bioforme that are enriched in the gut during infection. By evaluating bacterial mediated immune responses these studies will provide important new understanding about the mechanisms and functional aspects of these bacteria in regulating the immune system and their role in HIV disease.