Effect of blockage of the monocyte complement receptor type 1 (CR1, CD35) by monoclonal antibody J3D3 on the phagocytosis of nonparasitized normal and mutant (beta-thal trait) RBCs, and ring-parasitized and trophozoiteparasitized normal and mutant RBCs. Adherent monocytes (approximately 50 000 monocytes per well) were incubated at 37°C for 30 minutes with (+) or without (-)20 μg/mL purified anti-CR1 monoclonal antibody J3D3. After washing of the monocytes, phagocytosis of nonparasitized normal (□) and mutant (▪) RBCs, ring-parasitized and trophozoite-parasitized normal and mutant RBCs was performed as detailed in “Materials and methods.” Phagocytosis is expressed as number of phagocytosed RBCs per monocyte. Data are mean values ± SD (vertical bars). Numbers of separate experiments each performed with a different donor were as follows: nonparasitized normal and mutant RBCs, 4; ring-parasitized normal RBCs, 3; ring-parasitized mutant RBCs, 4; trophozoite-parasitized normal RBCs, 3; and trophozoite-parasitized mutant RBCs, 4. Significance of differences between treated cells (+) and their corresponding untreated (-) controls was assessed by t test for paired samples. ^*P < .001; ^**P < .01; and no asterisk, P > .05.