Model of the Intracellular Pathogen Response. Intestinal intracellular pathogens, like N. parisii and the Orsay virus, upregulate mRNA expression of a common set of C. elegans genes called the Intracellular Pathogen Response, or IPR genes. IPR genes can also be induced by proteotoxic stress, as well as by perturbation to purine metabolism. Independently of these triggers, they are also regulated by a pair of antagonistic paralogs called PALS-22 and PALS-25. Upregulation of IPR genes leads to increased resistance to pathogen infection