Neutrophil-derived MPO diminishes LPS-induced hypothermia and mortality. (A) Representative flow cytometry profile of Ly6G⁺ CD11b⁺ blood neutrophils 0 or 6 h after LPS injection in WT or Mpo^−/− mice. Areas outlined in red indicate values for neutrophils from the control (time 0) group; data are representative of results obtained in two independent experiments. (B and C) Changes in body temperature (Δ°C [mean ± SEM]; B) and survival (percentage of live animals; C) after LPS injection in WT and Mpo^−/− mice. (D) Survival after LPS injection in WT mice treated with the MPO inhibitor 4-ABAH or vehicle. Data in B–D are pooled from three independent experiments (total n = 11–13/group). **, P < 0.01; ***, P < 0.001 versus respective WT group (C) or vehicle-treated group (D) by Mantel–Cox log-rank test. (E) MPO in the peritoneal lavage fluid 6 h after injection with PBS (n = 4) or LPS (n = 7/group). Values from individual mice are shown; bars indicate means ± SEM pooled from two independent experiments. **, P < 0.01; ***, P < 0.001 versus PBS group and ^###, P < 0.001 versus LPS-treated control group by unpaired Student’s t test. (F–I) Bioluminescent visualization of MPO activity in various organs 6 h after injection of PBS or LPS in the indicated group. (F–H) Quantification of bioluminescence in spleen (F), liver (G), and lung (H). Data in F–H are means + SEM from three independent experiments (total n = 6–14/group) except for Mpo^−/− mice (two independent experiments with a total of three to four mice). *, P < 0.05; **, P < 0.01; ***, P < 0.001 versus PBS-treated WT group and ^#, P < 0.05; ^##, P < 0.01; ^###, P < 0.001 versus corresponding LPS-treated control group by unpaired Student’s t test. NS, not significant (P > 0.05). (I) Representative images of different organs (Sp, spleen; L, liver; St, stomach; C, cecum; Du, duodenum; Ki, kidney; H, heart; and L, lung). (J and K) Changes in body temperature (J) and survival (K) after LPS injection in DT-treated PMN^DTR mice (n = 9), PMN^WT littermate controls (n = 24), and PMN^DTR mice engrafted i.v. with 10⁷ purified BM neutrophils from WT mice (WT PMNs → PMN^DTR; n = 16) or from Mpo^−/− mice (Mpo^−/− PMNs → PMN^DTR; n = 10); arrows indicate days of i.p. injection of DT. Data are pooled from two (Mpo^−/− PMNs → PMN^DTR group), three (PMN^DTR group), or five (PMN^WT and WT PMNs → PMN^DTR groups) independent experiments. ***, P < 0.001 versus PMN^WT group and ^#, P < 0.05; ^##, P < 0.01 versus WT PMNs → PMN^DTR group by Mantel–Cox log-rank test.