Crry^−/− erythrocytes– and zymosaninduced AP complement activation. (A) Survival of biotin–labeled Crry^−/− mouse erythrocytes (10⁹) in wild-type (WT) or properdin^−/− mice. The percentage of Crry^−/− erythrocytes in the recipient mouse 5 minutes after transfusion was determined by FACS and taken as 100%. (B) Representative FACS analysis of C3 deposition on zymosan after incubation with WT, properdin^−/−, or factor B knockout (fB^−/−) mouse serum in Mg²⁺-EGTA. (C) Quantitation of C3 deposition on zymosan. Experiments were performed with 2 serum dilutions (1:10, 1:20) and 2 zymosan concentrations (0.025 mg/mL, 0.125 mg/mL). N = 3 mice per group. Error bars represent standard deviations. MFI indicates mean fluorescence intensity. P values refer to Student t test.