Functional Outcomes of Common and Rare IBD Associated Variants

The interplay between microbial and genetic susceptibility factors is central to the development of inflammatory bowel disease (IBD). Innate mechanisms, in particular through pattern recognition receptor (PRR) pathways, are the initiating drivers of host responses to microbes. Of the 163 loci associated to IBD, a broad range of likely genes modulate host responses to PRR at many levels, and confer some of the largest genetic effect sizes observed in autoimmunity. Despite the significant discoveries in IBD-associated polymorphisms over the past few years, the functional consequences of the vast majority of these loci have yet to be identified. A central outcome of PRR activation by bacterial and viral products is induction of cytokine secretion. To a large extent, IBD is characterized by dysregulated cytokines, and modulation of cytokines plays a primary role in IBD treatment. Inter-individual variation in PRR- induced cytokine secretion influences the balance between susceptibility to infection and inflammatory diseases. We hypothesize that polymorphisms in multiple IBD-associated genes contribute to inter-individual variation in PRR-induced cytokine secretion. Systematic, well- powered studies comprehensively defining the functional alterations driven by disease- associated human variation will provide enormous insight into central mechanisms of IBD; leveraging naturally occurring human genetic variation to systematic “perturb” an experimental system represents a highly innovative approach for precisely defining established and novel PRR-mediated mechanisms of cytokine secretion. Therefore, we will utilize a large, well- powered cohort to screen for IBD-associated polymorphisms contributing to the variation in PRR-initiated cytokine secretion across individuals, and then define the molecular mechanisms wherein the implicated IBD-associated genes, as well as the identified polymorphisms, regulate PRR-induced cytokine secretion.