A link between the p38 and UPR pathways has been shown in previous studies, although not with the level of functional relevance demonstrated here. Various arms of the UPR have been shown as both upstream or downstream of the p38 pathway, depending on the circumstances [25, 26, 27, 28, 29, 30] . The p38 pathway itself is implicated extensively in innate immune protection of many organisms against pathogens [31] and against PFTs in worms and mammals [6, 7] . Our data presented here for the first time functionally link the UPR to this major innate immune signal transduction pathway. Our findings on the activation and role of the UPR and p38 pathways in defense against PFT are summarized in Figure 6 .