Cutting edge: enhanced pulmonary clearance of Pseudomonas aeruginosa by Muc1 knockout mice.

MUC1 (MUC1 in human and Muc1 in nonhumans) is a membrane-tethered mucin that interacts with Pseudomonas aeruginosa (PA) through flagellin. In this study, we compared PA pulmonary clearance and proinflammatory responses by Muc1 −/− mice with Muc1 +/+ littermates following intranasal instillation of PA or flagellin. Compared with Muc1 +/+ mice, Muc1 −/− mice showed increased PA clearance, greater airway recruitment of neutrophils, higher levels of TNF-α and KC in bronchoalveolar lavage fluid, higher levels of TNF-α in media of flagellin-stimulated alveolar macrophages, and higher levels of KC in media of tracheal epithelial cells. Knockdown of MUC1 enhanced flagellin-induced IL-8 production by primary human bronchial epithelial cells. Expression of MUC1 in HEK293T cells attenuated TLR5-dependent IL-8 release in response to flagellin, which was completely ablated when its cytoplasmic tail was deleted. We conclude that MUC1/Muc1 suppresses pulmonary innate immunity and speculate its anti-inflammatory activity may play an important modulatory role during microbial infection.