Figure 2. p21 limits M1 activity during in vivo endotoxin tolerance.

P21^–/– and WT mice received 2 LPS doses as in Figure 1. (A) At 2 hours after the second LPS injection, macrophage populations from peritoneal exudates were analyzed by flow cytometry. Representative plots show gated CD11b^hiF4/80^lo and CD11b^hiF4/80^hi macrophages. The relative percentages of these 2 populations within the total F4/80⁺ gate, as well as total macrophage numbers, were similar for WT and P21^–/– mice after dual LPS or PBS treatment (right). Data show the mean ± SD (n = 8); NS, not significant. (B) Intracellular staining showed that after dual LPS challenge, TNF-α production by F4/80^lo macrophages was higher in P21^–/– compared with WT mice. Data show the mean ± SEM (n = 4); **P < 0.01. (C) After dual LPS treatment, intracellular TNF-α levels were elevated in P21^–/– F4/80^hi compared with WT macrophages. Data show the mean ± SEM (n = 4 mice), *P < 0.05, 2-tailed Student’s t test. SS, side scatter.