Mast cell specific negative regulation of LPS induced pro-inflammatory response by Itk and Btk (177.20)

Abstract

Abstract Gram-negative bacterial endotoxin lipopolysaccharide (LPS) induces mast cell secretion of pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, which is responsible for septic hypothermia. The non receptor tyrosine kinases Itk and Btk are both expressed in mast cells, and act as signaling regulators, but their roles in the response of mast cells to LPS are unclear. Here we show that Itk/Btk double knockout (DKO) mice suffered exacerbated and prolonged LPS induced hypothermia with increased TNF-α production by mast cells, compared to WT, Itk-/- and Btk-/- mice. This aggravated LPS induced hypothermia was recapitulated in mast cell deficient Sash mice reconstituted with DKO bone marrow derived mast cells (BMMCs). LPS (TLR4 ligand) stimulated DKO BMMCs exhibited hyperactive pro-inflammatory cytokine production with severely altered NF-κB signaling, which was not observed with Pam3CSK4 (TLR1/2 ligand). By contrast, DKO bone marrow derived macrophage and dendritic cells were not hyper-responsive to LPS as observed in DKO BMMCs, suggesting that Itk and Btk act as mast cell specific negative regulators in LPS/TLR4 signaling. Microarray analysis further revealed that the absence of Itk and Btk in mast cells significantly enhanced LPS induced pro-inflammatory program, which could potentially deteriorate endotoxin induced mast cell mediated inflammatory diseases.