CCP1-3 inhibits native PfRh4 erythrocyte binding and the CR1-PfRh4 invasion pathway. (A) Native PfRh4 binding to erythroid CR1 was inhibited by CCP1-3. Competitive binding assays were performed by incubating either CCP1-3 or CCP15-17 with invasion supernatants at the stated final concentrations of 4 μg/mL or 8 μg/mL. The black numbers in the top panel represent the percentage of PfRh4 binding relative to PBS for each concentration as determined by densitometry. Immunodetection of parasite proteins with anti-PfRh4 or anti-EBA-175 antibodies after erythrocyte binding is shown. (B) The PfRh4 invasion pathway was inhibited in the presence of CCP1-3. Parasite strains W2mefΔRh4 (gray bars, untreated erythrocytes) and 3D7 (black bars for untreated, white bars for nm-treated erythrocytes) were tested in growth assays in the presence of final concentrations of 0.5 mg/mL CCP1-3, CCP10-11, CCP15-17, CCP21-22, CCP15-25, or sCR1. Growth (percentage of control) on the y-axis refers to the percentage of parasitemia in the presence of CR1 constructs relative to the percentage of parasitemia with the addition of PBS (arbitrarily set to be 100%).