Intravenous transfer of CD11b^highLy6C⁺ spleen cells from P chabaudi–infected WT mice into CCR2-deficient mice reduces blood-stage parasitemia. (A) Characterization of cells used for adoptive transfer. Dual parameter contour plots and histogram showing purity and FACS profile of enriched CD11b^highLy6C⁺ spleen cells by magnetic-activated cell sorting (MACS) from WT C57BL/6 mice infected for 7 days with 10⁵P chabaudi and used in the transfer experiments. (Left) Contour plot showing CD11b and Ly6C expression. The number indicates the percentage of cells within the gated population. (Middle) Histogram showing expression of lineage markers. Number indicates the percentage of lineage-negative cells. (Right) Histogram of CD11c staining of the cells used for transfer. The number indicates the percentage of cells expressing low levels of CD11c. (B left) Course of a P chabaudi infection in CCR2^−/− mice (□) and CCR2^−/− given 15 × 10⁶ enriched CD11b^highLy6C⁺ cells on day 7 of their infection (■). As a comparison, the infection in C57Bl/6 mice is also shown (○). The values shown are the geometric means and SEMs of 4 mice. (Right) enlargement showing significant differences in parasitemias at days 15 and 17 of infection between CCR2^−/− mice (□) and CCR2^−/− given CCR2^+/+CD11b^highLy6C⁺ cells (■). Each symbol represents an individual mouse, and horizontal lines are the geometric means of 4 mice. P values were derived from the Mann-Whitney test; significant differences: *P = .001-.01, **P = .01-.05. The experiment was repeated twice.