Increased infiltration of neutrophils in the kidneys of S. aureus-infected C5aR1−/− and C5aR2−/− mice. Kidney tissue obtained from (A) uninfected, (B) infected wild type, (C) infected C5aR1−/− and (D) infected C5aR2−/− mice at 24 h after intravenous S. aureus inoculation was stained with anti-Ly6G antibodies. Original magnification, ×40 in (A), (C) and (D); ×20 in (B). (E) Quantification of Ly6G immunostaining in kidney sections of uninfected or S. aureus-infected wild type (white bars), C5aR1−/− (hatched bars) and C5aR2−/− (black bars) mice at 24 h after bacterial inoculation. Ly6G-staining in kidneys was quantified by digitalizing the section with a color video camera mounted on an Axiophot microscope with a 10× objective. In total, four fields per section were evaluated. Data are presented as percentage of stained area per kidney. *, p < 0.05. (F) Concentration of CXCL1 in kidney homogenates of uninfected or S. aureus-infected wild type (white bars), C5aR1−/− (hatched bars) and C5aR2−/− (black bars) mice at 12 h after bacterial inoculation. Data are given as pg/mL of tissue homogenate and reported as mean ± SD. *, p < 0.05.