Course of P yoelii YM parasite infection in mice. Groups of 5 BALB/c mice injected with mouse IgG2b anti-MSP1₁₉ (▴), human IgG1anti-MSP1₁₉ (□), human IgA1 anti-MSP1₁₉ (○), human IgG1anti-NIP (▪), human IgA1 anti-NIP (•), FcγRI × MSP1₁₉ diabody (♦), and PBS ▵. Each point represents the geometric mean parasitemia of mice in each group at the time after parasite challenge. All mice in the mouse IgG2b group survived for 6 months; all the mice in the other groups with high parasitemia were killed on either day 4 or day 5.