Neutralization of IL-33 reduces peripheral 5-HT and protects mice from LPS endotoxic shock. (A) Control IgG-Fc– or sST2-Fc–expressing plasmid was IV injected into Tph1^fl/fl and Vil1^creTph1^fl/fl mice. Relative 5-HT amounts in serum were assessed by ELISA. (B-G) IP injection of E coli serotype 055:B5 LPS into Tph1^fl/fl and Vil1^creTph1^fl/fl mice with 1-day pretreatment of IgG-Fc– or sST2-Fc–expressing plasmid. (B) Survival rate after LPS injection. (C) Flow cytometric analysis of lymphocytes isolated from peritoneum. (D) Quantification of frequency of gated F4/80⁻Ly6G⁺ neutrophils in panel C. (E) Quantification of F4/80⁻Ly6G⁺ neutrophils isolated from peritoneum 4 hours after LPS injection. (F) Tumor necrosis factor-α (TNF-α) levels in the serum at 24 hours after LPS injection. (G) Body temperature was measured at 0 and 4 hours after LPS injection. Data are representative of 2 independent experiments (C) or are pooled from 2 independent experiments (A-B, D-G). *P < .05, **P < .01, ***P < .001 by Student t test. Error bars represent standard deviation. NS, not statistically significant.