C5aRA attenuated hyperoxia-induced total cell counts and the number of macrophages, neutrophils and lymphocytes in BALF. Following treatment with 100% oxygen for 36 h with or without C5aRA treatment, BALF was collected. The total cell count and the number of macrophages, neutrophils and lymphocytes in BALF were determined by examination of cytocentrifuge slides and hemocytometer. (A) Hyperoxia increased the total cell count and the number of (B) macrophages, (C) neutrophils and (D) lymphocytes in BALF from 100% oxygen-treated mice. The hyperoxia-induced increases in total cell counts and the number of macrophages, neutrophils and lymphocytes in BALF were all significantly reduced in mice receiving C5aRA. Data were normalized with cell numbers and are expressed as mean ± SD (n=5). **P<0.01, hyperoxia vs. control; ##P<0.01, #P<0.05, hyperoxia + C5aRA vs. hyperoxia. C5aRA, C5a receptor antagonist; BALF, bronchoalveolar lavage fluid.