Sustained acute-stage parasitemia and delayed weight gain in P chabaudi–infected C57Bl/6 CCR2^−/− mice compared with WT mice. (A) Contour plots showing CD11b and Ly6C expression in bone marrow (left) and spleen (right) of CCR2-deficient and WT C57Bl/6 mice infected for 8 days with P chabaudi. Number indicates percentage of CD11b^highLy6C^high bone marrow monocytes within the region shown. The same gating strategy as described in Figure 1 was used to obtain the CD11b versus Ly6C contour plots of the spleen cells. Number indicates percentage of CD11b^highLy6C⁺ monocytes in the gated populations. (B) Total numbers of CD11b^highLy6C^high monocytes in the bone marrow (left) and the CD11b^highLy6C⁺ monocytes in the spleen (right) of CCR2^−/− (□) and WT C57Bl/6 (■) mice after 8 and 11 days of infection. The values shown represent the means and SEMs of 4 mice. P values are shown (Student t test). (C) Parasitemia (left) and body weight (right) in P chabaudi–infected CCR2^−/− (open symbols) and WT (closed symbols) C57Bl/6 mice. Mice were infected intraperitoneally with 10⁵ iRBCs, and the course of infection and weight was followed for 22 days. Weight is expressed as the percentage of the starting weight at day 0. Significant differences: *P = .001-.01, **P = .01-.05 (Mann-Whitney test) between WT and CCR2^−/− mice. The values shown represent the means and SEMs of 5 to 10 mice in each group.