In vitro binding of rhCD59-P to erythrocytes and its consequences. (A-B) Guinea pig whole blood was washed and incubated in the presence or absence of either rhCD59-P or the control compound rhCD59 at the concentrations indicated. In panel A, blood cells were then washed and incubated with a fluorescently labeled anti–human CD59 antibody and compound binding was visualized by fluorescence microscopy. Corresponding brightfield images are also shown. In panel B, a hemolytic “reactive lysis” assay was performed on the guinea pig erythrocytes as described in “Reactive lysis assay.” In panel C, a Ham assay was performed on washed whole blood from PNH patient volunteers in the presence or absence of either rhCD59-P (solid line) or rhCD59 (dotted line). Data points show means of direct hemolysis ± SDs of triplicate values. A representative experiment is shown.