Df restores the deficiency of alternative pathway activation in Masp1/3^−/− mice. (A) Immunoblot analysis of Bf incubated with the sera of wild-type C57BL/6 (WT), MBL-A, and -C double-deficient (Mbl null) and Masp1/3^−/− mice at 37°C for 30 min. Each serum type was incubated with (+) or without (−) 1.25 µg C3(H₂O). Serum from Masp1/3^−/− mice was also incubated with (+) human Df (0.2 µg). Note: an additional band (∼26 kD) was also detected with Ba, but it was not identified. (B) A hemolytic assay using rabbit erythrocytes was performed. Percent hemolysis induced by sera (25 µl) from wild-type (WT), Masp1/3^−/− (M1/3^−/−), and Masp1/3^−/− mice supplemented with 0.2 µg human Df (huDf) is indicated. (C) A C3 deposition assay on immobilized zymosan was performed. 5 µl of sera from wild-type (WT), Masp2/sMap^−/− (M2^−/−), and Masp1/3^−/− (M1/3^−/−) mice supplemented with 0.2 µg human Df (huDf) were analyzed. Data are presented as the means ± SD of three independent experiments.