Increased susceptibility of female mice to LPS-induced endotoxic shock. (A) Experimental design for survival analysis following LPS-induced endotoxic shock. (B) Retrospective survival analysis of 8- to 16-week-old C57BL/6 male (n = 110) and female (n = 93) mice after IP injection of 5 to 7.5 mg/kg LPS. (C-H) Baseline frequencies of immune cell populations in the PBL of male (n = 104) and female (n = 102) mice: (C) CD19⁺MHCII⁺ B cells, (D) CD3⁺CD4⁺ T cells, (E) CD3⁺CD8⁺ T cells, (F) NK1.1⁺ NK cells, (G) CD11b⁺Ly6G^– monocytes, and (H) CD11b⁺Ly6G⁺ neutrophils. (I) Experimental outline for assessing CD11b⁺Ly6G⁺ neutrophil frequency in relation to sex and survival following LPS shock. (J) Baseline frequency of CD11b⁺Ly6G⁺ neutrophils in PBLs, stratified by survival outcome after LPS-induced endotoxic shock. Each dot represents an individual mouse. Data are presented as mean ± standard error of the mean (SEM). Survival curves were analyzed using the log rank (Mantel-Cox) test. Statistical significance of immune cell frequency differences was determined using 2-tailed t tests (Mann-Whitney U tests). P values < .05 were considered to indicate statistical significance. ∗P < .05; ∗∗P < .01; ∗∗∗∗P < .0001. ns, not significant.