Toll-like Receptor 2 Is Essential for the Sensing of Oxidants during Inflammation

Abstract

Rationale: The mechanisms by which oxidants are sensed by cells and cause inflammation are not well understood. Objectives: This study aimed to determine how cells “sense” soluble oxidants and how this is translated into an inflammatory reaction. Methods: Monocytes, macrophages, or HEK293 cells (stably transfected with human Toll-like receptor [TLR]2, TLR2/1, TLR2/6, or TLR4/MD2-CD14) were used. CXC ligand-8 (CXCL8) levels were measured using ELISA. Phosphorylated IL-1 receptor–associated kinase 1 levels were measured using Western blot. TLR2^−/− and TLR4^−/− mice were challenged with oxidants, and inflammation was measured by monitoring cell infiltration and KC levels. Measurements and Main Results: Oxidants evoked the release of CXCL8 from monocytes/macrophages; this was abrogated by pretreatment with N-acetylcysteine or binding antibodies to TLR2 and was associated with the rapid phosphorylation of IL-1 receptor–associated kinase 1. Oxidants added to HEK293 cells transfected with TLR2, TLR1/2, or TLR2/6 but not TLR4/MD2-CD14 or control HEK nulls resulted in the release of CXCL8. Oxidant challenge delivered intraperitoneally (2–24 hours) or by inhalation to the lungs (3 days) resulted in a robust inflammation in wild-type mice. TLR2^−/− mice did not respond to oxidant challenge in either model. TLR4^−/− mice responded as wild-type mice to oxidants at 2 hours but as TLR2^−/− mice at later time points. Conclusions: Oxidant–TLR2 interactions provide a signal that initiates the inflammatory response.