The presence of the mucoid phenotype of Pseudomonas aeruginosa is a marker of poor survival in cystic fibrosis. As CF lung disease results from chronic infection leading to airway inflammation, we determined whether the switch to a mucoid phenotype by P. aeruginosa has an impact on the inflammatory response of airway epithelial cells. Exposure of airway epithelial cells to non-mucoid and mucoid P. aeruginosa-derived material leads to p38 alpha MAPK activation, a key protein kinase involved in transmitting inflammatory signals. However, while the non-mucoid strain PAO1 activates p38 alpha. MAPK pathway solely via TLR5, the mucoid strain PACF508 activates p38 alpha MAPK via both TLR5 and TLR2. Inactivation of mucA (the gene responsible for the mucoid phenotype) in PAO1 leads to p38 alpha MAPK activation by both TLR2 and TLR5, as observed in the clinical mucoid isolate PACF508. Therefore, the switch to mucoid phenotype may contribute to more inflammation via TLR2. activation in addition to TLR5. Our findings highlight an important and under recognized role for TLR2 in the response of airway epithelial cells to infection. (C) 2012 Elsevier Inc. All rights reserved.