LPS challenge induces higher iNOS expression and greater MAPK and NF-κB activation in peripheral myeloid cells from female mice compared with male mice. Experimental setup: age-matched male and female mice were injected IP with 5 mg/kg LPS. PBLs were collected 6 hours after injection, and analyzed via flow cytometry for immune cell frequencies, activation markers and signaling pathway activation. (A) Representative flow cytometry plots (left) and cumulative frequencies (right) of CD4⁺ and CD8⁺ T cells in PBLs from 1-day LPS-treated male and female mice. (B) Representative flow plots (left) and cumulative frequency (right) of CD19⁺MHCII⁺ B cells in PBLs from 1-day LPS-treated male and female mice. (C) Representative flow plots (left) and cumulative frequency (right) of CD11b⁺Ly6G⁺ neutrophils and CD11b⁺Ly6G^– monocytes in PBLs from 1-day LPS-treated male and female mice. (D) Representative flow plots (left) and cumulative frequency (right) of NK1.1⁺ NK cells in PBLs from 1-day LPS-treated male and female mice. (E) Representative flow plots (left) and cumulative frequency (middle) of CD11c⁺MHCII⁺ DCs in PBLs from 1-day LPS-treated male and female mice. Mean fluorescence intensity of MHCII expression on DCs (right). (F) Frequencies of CD14⁺, TLR4⁺, arginase-positive, and iNOS-positive populations among CD11b⁺Ly6G^– monocytes from 1-day LPS-treated male and female mice. (G) Frequencies of CD14⁺ and TLR4⁺ populations among CD11b⁺Ly6G⁺ neutrophils from 1-day LPS-treated male and female mice. (H) Frequencies of the phosphorylated (p)–NF-κB⁺, p-ERK⁺, p-P38⁺ and p-JNK⁺ populations among CD11b⁺Ly6G^– monocytes from 1-day LPS-treated male and female mice. (I) Frequencies of the p–NF-κB⁺, p-ERK⁺, p-P38⁺ and p-JNK⁺ populations among CD11b⁺Ly6G⁺ neutrophils from 1-day LPS-treated male and female mice. Each dot represents data from an individual mouse. Statistical significance was determined using 2-tailed t tests (Mann-Whitney U tests) for 2-group comparisons. P values < .05 were considered to indicate statistical significance. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001. ns, not significant.