Interaction of the WT and mutant factor B proteins with the novel ligand iC3b. (A) ELISA assay with iC3b-coated plates (average ± SD, n = 3). (B) SPR measurement of factor B proteins binding to iC3b coupled to CM5 chip. (C) Hemolytic assay for the C3-convertase forming capacity of WT and mutant factor B proteins on iC3b-coated erythrocytes. One representative experiment of 3 performed is given.