Submitted on July 16, 2007
Accepted on July 9, 2008
Innate Immune Responses in Murine Pleural Mesothelial Cells: Toll-like Receptor-2 Dependent Induction of 
-Defensin-2 by Staphylococcal Peptidoglycan
Tajamul Hussain1, Najmunnisa Nasreen2, Yimu Lai3, Brendan F. Bellew4, Veena B Antony2, and Kamal Abdul Mohammed5*
1 Pulmonary Madicine, University of Florida, Gainesville, Florida, United States
2 Pulmonary Medicine, University of Florida, Gainesville, Florida, United States
3 pulmonary Medicine, University of Florida, United States
4 Medicine, University of Florida College of Medicine, Gainesville, Florida, United States
5 Division of Pulmonary Critical Care Medicine, Department of Medicine, University of Florida, Gainesville, Florida, United States
* To whom correspondence should be addressed. E-mail: mkamal{at}medicine.ufl.edu.
The innate immune response is mediated in part by pattern recognition receptors including toll-like receptors (TLRs). Pleural mesothelial cells (PMCs) that line the pleural surface are in direct contact with pleural fluid and accordingly carry the risk of exposure to infiltrating microorganisms or their components in an event of a complicated parapneumonic effusion. Here we show that murine primary PMCs constitutively express TLRs1-9 and upon activation with PGN, mouse PMC produce antimicrobial peptide 
-defensin-2 (mBD2). Treatment of PMCs with staphylococcal peptidoglycan (PGN), a gram positive bacterial cell wall component and a TLR2 agonist, resulted in a significant increase in TLR2 and mBD2 expression. Silencing of TLR2 expression by small interfering RNA (siRNA) led to down regulation of PGN induced mBD2 expression thereby establishing causal relationship between the activation of TLR2 receptor and mBD2 production. PMCs exposed to PGN showed increased p38 MAPK activity. In addition, PGN induced mBD2 expression was attenuated by SB203580, a p38 MAPK inhibitor underlining the importance of p38 MAPK in mBD2 induction. Inhibition of erk1/erk2 or PI3K did not block PGN induced mBD2 expression in PMC. PGN activated PMC derived mBD2 significantly killed S. aureus and mBD2 neutralizing antibodies blunted this antimicrobial activity. Taken together these data indicate that PMCs may contribute to host innate immune defense upon exposure to gram positive bacteria or their products within the pleural space by up regulating TLR2 and mBD2 expression.
