PfRh4-CR1 pathway constitutes the majority of sialic acid-independent invasion events. (A) Sialic acid–dependent and –independent parasite strains. Parasite strains were assayed for their ability to invade nm-treated erythrocytes. The y-axis represents percentage of growth of parasites into nm-treated erythrocytes relative to growth of parasites into untreated erythrocytes. (B) Expression of PfRh4 in P falciparum strains. Western blot of saponin-lysed schizont pellets probed with anti-PfRh4 monoclonal antibody 2E8 (top panel) and anti–EBA-175 rabbit polyclonal antibody (bottom panel). (C) Growth of sialic acid–independent strains in untreated erythrocytes was slightly inhibited in the presence of CCP1-3. Parasite strains were tested in growth assays into untreated erythrocytes in the presence of 0.5 mg/mL final concentration of CCP1-3 (white bars) or BSA (black bars). Growth (percentage of control) on the y-axis refers to the percentage parasitemia in the presence of CCP1-3 or BSA relative to the percentage parasitemia with the addition of PBS, which is arbitrarily set at 100%. (D) Growth of sialic acid-independent strains in nm-treated erythrocytes was inhibited in the presence of CCP1-3. Parasite strains were tested in growth assays using nm-treated erythrocytes in the presence of 0.5 mg/mL CCP1-3 (white bars) or BSA (black bars).