The intestinal epithelium represents one of the first lines of defense against pathogenic bacteria. Immune regulation at this critical barrier is necessary to maintain organismal fitness, and mis-regulation here has been linked to numerous debilitating diseases. Functional relationships between the nervous system and immune system have been found to be critical in the proper coordination of immune defenses at barrier surfaces, however the precise mechanisms underlying theses interactions remains unclear.

Through conducting a forward genetic screen utilizing the model organism Caenorhabditis elegans, we uncovered a surprising requirement for the olfactory neuron gene olrn-1 in the regulation of intestinal epithelial immunity. During nematode development, olrn-1 is required to program the expression of odorant receptors in the AWC olfactory neuron pair. Here, we show that olrn-1 also functions in AWC neurons in the cell non-autonomous suppression of the canonical p38 MAPK PMK-1 immune pathway in the intestine. Low activity of OLRN-1, which activates the p38 MAPK signaling cassette in AWC neurons during larval development, also de-represses the p38 MAPK PMK-1 pathway in the intestine to promote immune effector transcription, increased clearance of an intestinal pathogen and resistance to bacterial infection. However, derepression of the p38 MAPK PMK-1 pathway also results in severe developmental and reproductive defects, demonstrating the critical function of OLRN-1 to both prime C. elegans intestinal epithelial cells for the induction of anti-pathogen responses, and to limit the deleterious effects of immune hyper-activation. These data reveal an unexpected connection between olfactory receptor development and innate immunity, as well as demonstrate how neuronal regulation of immune responses within the intestinal epithelium is critical for both reproductive and developmental fitness.