CCL2 and neoplasm: As shown in Figure 5B, the majority of tumor cell clones recovered from the metastatic lung tumors of both WT and MCP-1−/− mice constitutively expressed higher levels of MCP-1 mRNA and produced higher levels of MCP-1than the original 4T1 cells, leading to the hypothesis that higher MCP-1 expression by tumor cells may also support lung metastasis.