PLUNC is a secreted product of neutrophil granules

Airway epithelia and neutrophils are frequently recruited to release host defense factors in response to a variety of pulmonary pathogens. One abundant product of airway epithelia is palate, lung, nasal epithelium clone (PLUNC), a proposed innate immune protein expressed in submucosal glands and surface airway epithelia. In this study, we report the expression of PLUNC in human neutrophils, a previously unrecognized source of this protein. Immunoblots performed on polymorphonuclear cell (PMN) lysates and PMN subcellular fractions indicated that PLUNC was present in the specific granules of the neutrophil. Furthermore, secretion assays demonstrated that PLUNC protein was released by neutrophils upon stimulation with secretogogues, including formyl methionyl leucyl phenylalanine and the calcium ionophore A23187. Although recombinant PLUNC protein failed to exhibit antibacterial activity in our studies, its storage and secretion by a professional phagocytic cell support the hypothesis that PLUNC participates in an aspect of the inflammatory response that contributes to host defense. These studies suggest that PLUNC expression is less restricted than previously believed, and highlight new avenues of research for the study of PLUNC function.