PROJECT SUMMARY Diarrheal disease is the second leading cause of death in children under five years of age. Understanding the processes involved in bacterial pathogenesis and host response to enteric pathogens is essential to improve treatment and develop effective prevention strategies. Such studies have been hindered by the lack of reliable models that fully recapitulate the complex cellular and molecular events and interactions that take place in the human gut. Our collaborators at JHU established in vitro model systems consisting of primary human epithelial cells from the small and large intestine (enteroid/colonoid) generated from intestinal stem cells from biopsy or resected tissue. The Immunology Core (IC), in collaboration with the Enteroid Core, will further refine this model system by adding to the enteroid and colonoid cultures, functionally active primary innate immune cells with the goal of producing a multi-cellular model that will more closely resemble the human gut. This physiologically relevant system will generate new insights into human innate mucosal immunity, the interplay between epithelial and immune cells, and the role of innate immune cells during enteric infections. The IC will also support the studies to be performed under the different projects by measuring cytokines and chemokines service, facilitating access to human blood for cell differentiation and isolation, providing training and making available our technical expertise and resources. The work to be conducted by the IC is divided in two Aims. In Aim 1, as a core developmental task, macrophages and dendritic cells (DC) differentiated from peripheral blood monocytes and polymorphonuclear neutrophils (PMN) isolated from peripheral blood will be individually added to the basolateral side of enteroid/colonoid monolayers. Tissue structure and integration, cell phenotype, viability and functionality will be assessed by multiple methods including confocal microscopy, western blot and flow cytometry. We will also determine the functional traits on engrafted immune cells (e.g. phagocytosis for DC and macrophages, translocation for PMN, production of cytokines, chemokines and immune mediators), morphological changes (i.e. membrane projections for macrophages and DC, presence of neutrophil extracellular traps for PMN) and the expression of activation/phenotypic markers. Optimal conditions for the generation of the robust enteroid/colonoid-innate immune cell model and procedures will be made available to the research projects for the use in their specific studies. In Aim 2, as a core service task, we will measure cytokines, chemokines and immune mediators produced by gut epithelial and innate immune cells (under different experimental conditions) to support studies performed under all projects. Collectively, the work proposed will generate new knowledge on enteric infection and immunity that will inform vaccine development and therapeutic efforts.