A hallmark of cystic fibrosis (CF) lung pathology is the accumulation of bacteria, usually including Pseudomonas aeruginosa, and the triggering of an exuberant innate immune response, i.e., increased production of proinflammatory cytokines and chemokines and resulting recruitment of neutrophils to fight the infection. These events lead to characteristic damage to and remodeling of lung tissue characteristic of the disease. It has been proposed that this so-called hyperinflammatory response in CF results from a defect in the epithelial cells resulting in altered inflammatory signaling and increased release of proinflammatory mediators. This presentation will first summarize previous work from this lab in which this hypothesis was tested and discarded. The second part of the talk will present an alternative model based on recent experiments that indicate that an important aspect of wtCFTR’s role in controlling innate immune response is through its role as a cAMP/PKA-activated anion channel. Using an adenovirus to express either wtCFTR or ΔF508CFTR in human CF airway epithelial cells in culture, we found that there was no role for CFTR in proinflammatory NF-κB or Ca signaling or in IL8 secretory responses to either Pseudomonas aeruginosa or flagellin, the key activator of toll-like receptor 5 in the epithelial cells. Expression of wtCFTR or ΔF508CFTR also had no effect on cytosolic or organelle redox or on the unfolded protein-stress response of the endoplasmic reticulum. It is proposed instead that the most important aspect of the wtCFTR in the innate immune response is its “classical” function as an anion channel. Transepithelial electrophysiology showed that wtCFTR is activated by both bacterial exoproducts (flagellin, pyocyanin, homoserine lactone) and also by proinflammatory mediators (IL1β, TNFα). It is expected that the presence of Pseudomonas aeruginosa in the airways will trigger secretion of proinflammatory mediators, and both the bacteria and the cytokines and chemokines will increase wtCFTR-dependent chloride and bicarbonate secretion and osmotically obliged fluid into the airway surface liquid. This fluid secretion will help flush the bacteria from the airways in nonCF but will be missing in CF, leading to accumulation of bacteria and increased proinflammatory response. An unexplained aspect of this proposal is that wtCFTR is activated by cAMP/PKA, while none of the bacterial or proinflammatory mediators has been thought to activate this pathway. For example, the quorum-sensing molecule N-3-oxododecanoyl homoserine lactone (3OC12-HSL or C12) that Pseudomonas aeruginosa use to control expression of both virulence factors and biofilm in the airways has been shown to activate Ca signaling in several cell types, but not cAMP. Recent experiments on cultured human nonCF and CF cells in vitro using transepithelial and patch clamp electrophysiology and wide field, confocal and TIRF imaging methods show that C12 activates cAMP signaling through a store-operated cyclase model in which C12 activates IP3 receptors, which then leak Ca from the endoplasmic reticulum into the cytosol. The loss of Ca from the ER activates the ER-resident, Ca-sensitive protein regulator stim1, which migrates to the plasma membrane and activates a still to be identified adenylate cyclase in the plasma membrane to produce cAMP and activate CFTR. It seems likely that many bacterial and proinflammatory mediators trigger wtCFTR using a similar activation of cAMP in addition to their better known effects on NF-κB/p38 and Ca signaling.