Fig. 2. In aged mice, the increase in number of circulating polymorphonuclear cells after lipopolysaccharide challenge is higher than in young mice. (A ) Flow cytometrical analysis of representative blood samples of a 3-month and 18-month-old mouse with and without lipopolysaccharide injection. In each scatter plot, the right upper quadrant represents polymorphonuclear cells (Ly-6G and CD11b-positive). The relative increase in polymorphonuclear cells count after lipopolysaccharide administration is lower (*P < 0.05) in 3 months compared with aged mice. Value as % of polymorphonuclear cells of total leukocyte count (±SD) of n = 3. (B ) Quantification of myeloperoxidase (MPO) levels in plasma assessed by ELISA (mean [SD], n = 8 per group; *P < 0.05, by ANOVA with post hoc comparison of all groups using Bonferroni correction). LPS = lipopolysaccharide.