The monoclonal antibody 5F5G1 recognizes SPLUNC1. The human genome encodes eight different PLUNC (palate, lung, and nasal epithelium associated) proteins that share a predicted structural similarity. The 25 kDa SPLUNC1/BPIFA1 protein was the first identified PLUNC protein and issecreted in human sputum and tracheobronchial secretions, as well as in saliva, nasal lavage fluid, and in specific granules of human neutrophils. The biological function of SPLUNC1/BPIFA is not known, but structural similarities to BPI family proteins suggest that SPLUNC1/BPIFA may be involved in defense responses in the airways. This proposed function is supported by the finding that SPLUNC1 levels are elevated in chronic airway inflammation and that mice overexpressing SPLUNC1/BPIFA exhibit enhanced protection against P. aeruginosa.Moreover, the protein was reported to bind LPS and shown to play and essential role in pulmonary host defense against Klebsiella pneumoniae respiratory infection. The monoclonal antibody, 5F5G1, is specific for SPLUNC1/BPIFA and can be used for ELISA, western blot and immunohistochemistry.