Lactate suppression of TLR4 requires GPR81 and ARRB2. RAW 264.7 cells were treated with siRNA for Gpr81, Arrb2, or scramble siRNA and assessed for Gpr81 and Arrb2 knockdown (A and D).Pro-Il1β induction was measured in siRNA treated cells stimulated with LPS and lactate (B and E). Murine peritoneal macrophages were treated with LPS and the GPR81 agonist 3-chloro-5hydroxybenzoic acid 100 mM and phospho-p65 NF-κB levels assessed (C). RAW 264.7 cell were treated with or without lactate, and cell lysates then immunoprecipitated (IP) with anti-GPR81 antibody or control serum, and immunostained for ARRB2 and GPR81 (F). Asterisks denote significant difference (P<0.05) between treatment or bracketedgroups when marked. NS, not significant.