Neonatal mice demonstrate altered peritoneal cell content and function compared with adult mice. Percentages (A) and phagocytic activity (B) (Dil⁺) of B220⁺CD11b⁺ peritoneal B1 cells and GR-1⁺Ly6C^lowCD11b^high neutrophils (PMN) from neonates versus young adults. Percentage of Dil⁺ cells refers to percentage of that cell population that registered greater than the baseline MFI (expressed as greater than 1000 MFI). Data shown are representative of 4 separate identical experiments. Bar graphs represent means with error bars representing standard deviations (*P < .05 by Student t test).