UC Davis

Interactions among intestinal bacteria and the immune system contribute to the maintenance of a functional intestinal barrier in healthy individuals, and possibly to systemic immune activity. We hypothesized that intestinal bacteria would be associated with systemic biomarkers of innate and adaptive immune responses in healthy adults. 79 immune function markers were subjected to factor analysis resulting in 17 Immune Factors (IFs), each composed of 2-10 immune variables. Bacterial taxa from stool samples were identified at the family and genus levels by 16S rRNA amplicon sequence analysis and their read counts and relative abundances were utilized in a multiple linear regression model to identify microbial taxa associated with the IFs. A total of 10 significant associations were identified between bacterial taxa and IFs. The family Rikenellaceae showed a positive association with innate IF5 (including 5 chemokines, 2 cytokines, 2 adhesion molecules, and the macrophage metabolite neopterin) and a negative association with adaptive IF4 (including T-cells with activation marker HLA-DR). Additionally, Pseudomonadaceae and its genus Pseudomonas showed a negative relationship with innate IF5, and adaptive IF13 (including T-cell cytokines IL-10, IL-17, and IFN-γ) was negatively associated with Butyrivibrio and positively associated with Slackia. These associations suggest ongoing interactions between gut bacteria and the systemic immune system in healthy adults. The association of these taxa with the IFs may result from specific microbial-immune system interactions that play a role in maintenance of a healthy barrier integrity in our cohort of healthy adults. IMPORTANCE Chronic inflammation may develop over time in healthy adults as a result of a variety of factors, such as poor diet directly affecting the composition of the intestinal microbiome, or by causing obesity, which may also affect the intestinal microbiome. These effects may trigger the activation of an immune response that could eventually lead to an inflammation-related disease, such as colon cancer. Before disease develops it may be possible to identify subclinical inflammation or immune activation attributable to specific intestinal bacteria normally found in the gut that could result in future adverse health impacts. In the present study, we examined a group of healthy men and women across a wide age range with and without obesity to determine which bacteria were associated with particular types of immune activation to identify potential preclinical markers of inflammatory disease risk. Several associations were found that may help develop dietary interventions to lower disease risk.