|Ph.D Student||Vainberg Shiran|
|Subject||Gut Microbiota and Host Immune Interactions|
|Department||Department of Biotechnology and Food Engineering||Supervisors||Professor Yechezkel Kashi|
|Professor Yehuda Chowers|
|Full Thesis text|
The gut is a habitat for complex bacterial community, which consistently interacts with the immune-system. There is accumulative data about numerous disease-associated alternations in gut microbiota composition.
In the present research we investigated the cause and effect relationship between the immune-system and the gut microbiota by manipulating these components in two experimental models. Our results suggest that gut microbiota has a dominant role in microbial-immune interactions, that under dysbiotic conditions, can induce increased immune response which is associated with inflammation and tissue damage.
In the first part of this study we used bone marrow transplantation (BMT) model in a defined genetic setup that simulated the natural genetic and microbiome variation among individuals and assured avoidance of graft versus host responses, to investigate the effect of immune-system replacement on the microbiome. We found that in a host with mature microbiota, immune-system manipulation had only mild impact on microbiota composition, with the majority of the OTUs remaining stable and only few specific OTUs responding, in which the most prominent OTU was Rikenellaceae that was highly influenced by the immune-system replacement.
At the second part of the study we used a model of radiation proctitis (RP) to investigate the microbiota and immune-system interactions in the context of disease-associated alteration in the microbiota, when both components are simultaneously unbalanced by radiation. Complementary to the BMT results, the RP model demonstrated the impact of the microbiota composition on immune parameters and aggravation of tissue damage, and beyond the basic research question it further stressed the clinical relevance of the microbial dysbiosis to RP disease progression, tissue damage and inflammation. We showed that radiation induced changes in the microbial composition that was correlated with cytokine expression and histopathology, presenting unique signature in different clinical stages. We showed that the dysbiotic microbiota had an inflammatory impact on epithelial cells that was expressed by upregulation of IL-1β and TNFα. This effect was further assessed by using in-vivo experiments of two different germ free mouse models, which demonstrated that post-radiation microbiota predisposed the mice to both radiation damage and inflammatory trigger (DSS), and that it was accompanied by induction of intestinal expression of IL-1β. The role of IL-1 in the inflammatory response progression by the microbiota was supported by the reduction of tissue damage by injection of IL-1 receptor antagonist to irradiated mice.
By sequencing the colonic T-cell receptor β chain (TCRB) of irradiated and naïve mice from the irradiated and adjacent colonic sites, we also observed specific radiation-induced response of colonic T-cells showing TCRB diversification with high within-sharing ratio and increased high-level convergent recombination in the irradiated area, possibly linked to radiation-induced Ags-driven selection. Correlation analyses of the TCRB and the dysbiotic microbiota suggested potential bacterial species and proteins that may be involved in bacteria- T-cell interactions post-radiation.
Collectively, our finding may suggest intestinal microbiota manipulation as a potential therapeutic approach to improve the outcome of intestinal diseases that involve inflammatory processes which accompanied by microbial dysbiosis in general, and in radiation proctitis in particular.