CCL2 and neoplasm: As shown in Figure 2A, high levels of MCP-1 mRNA were detected in the original tumors grown in WT or MCP-1−/− mice (lanes 2–5), but the levels of MCP-1 mRNA expressed by LLC cells isolated from tumors either from WT or MCP-1−/− mice (mouse #4 and 5 presented in Figure 1B) were low (lanes 6–9) and comparable to that in the original LLC cells used for injection (lane 1), supporting the hypothesis that MCP-1 expression is not constitutively elevated in tumor cells, but rather, activation of tumor cells in a tumor microenvironment is the cause of elevated MCP-1 expression by tumor cells in vivo.