Immunity at the edge: cell-intrinsic roles for intestinal epithelial cells in host immunity

As the barrier between the contents of the intestines and the rest of the body, intestinal epithelial cells (IEC) occupy a crucial niche for the health of the organism. They are responsible for nutrient absorption and transfer, barrier maintenance, and interactions with the massive community of microorganisms that live in the gut. While this community primarily includes commensal microbes, many pathogens use the gastrointestinal tract as an initial site of infection. IEC are important as a physical barrier, but a growing body of research demonstrates their importance as active participants in host immunity. In this review, we discuss the role of IEC in responding to infection by intracellular bacteria, parasites, and viruses. IEC express an array of intracellular sensors to rapidly detect invading pathogens and initiate cytokine production. In addition, IEC are equipped to present antigen to T cells, and express co-stimulatory molecules that enhance or limit T cell responses, although the impact of these interactions remains unclear. Determining how IEC participate in host immunity and pursuing the open questions we identify in this review will be broadly important for understanding infection and immunity in the gastrointestinal tract.