The monocyte chemotactic protein 3 (MCP-3) belongs to the MCP subgroup of the CC chemokines and promotes chemotaxis of immune cells. MCP-1 is believed to play an important role in monocyte infiltration into tumor tissues; however, the relationship between tumor-infiltrating macrophage/microglia (TIM/M) and the expression of chemokines has not been investigated in detail in human glioma samples; therefore, we first examined the expression of several chemokines and chemokine receptors in human tumor cell lines, which included glioma lines, using real-time PCR. We found that several glioma lines expressed MCP-3 predominantly, and not MCP-1. In order to assess the significance of MCP-3 expression in human glioma tissues, we then examined the number of CD68+ TIM/M, the percentage of TIM/M in the total cell population, and the expression of MCP-1 and MCP-3 in glioma tissues. There was a correlation between the percentage of TIM/M and MCP-3 expression levels; however, there was no correlation between the percentage of TIM/M and MCP-1 expression. There was no correlation between the number of TIM/M and prognosis of patients. These data indicate that tumor cell-derived MCP-3, but not MCP-1, facilitates the infiltration of macrophage/microglia into tumor tissues. This is the first study that clearly compared the significance of MCP-3 with that of MCP-1 in the tumor infiltration rates of TIM/M.

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