Chemokine receptor usage for accumulation of MDSCs in tumor. 3LL tumors were subcutaneously inoculated to WT, CCR1^−/−, CCR2^−/−, CCR5^−/−, or CX₃CR1^−/− mice. Seven days after tumor inoculation, when tumor grew to 6-10 mm in diameter, tumor-infiltrating leukocytes were analyzed by a flow cytometry. (A) Representative flow cytometric profiles of tumor-infiltrating CD45⁺CD11b⁺ cells in WT and CCR2^−/− mice. (B) Percentage of CD11b⁺ cells, macrophages, and neutrophils in CD45⁺ leukocytes from tumors of WT or chemokine receptor-deficient mice. (C) Percentage of CD11b⁺ cells, macrophages, and neutrophils in CD45⁺ leukocytes from B16 tumor of WT or CCR2^−/− mice. (D) Cryosections of tumors from CCR2^+/+ and CCR2^−/− mice were subjected to immunofluorescent staining with antibodies to CD11b (green), F4/80 (red), type IV collagen (blue). Representative image of 3 mice for each group. (B,C) Graphs represent the mean (± SD) of 3-5 mice. *P < .05; **P < .01.