Are tumor-infiltrating macrophages derived from monocyte-lineage belonging to the myeloid-derived suppressor cell?

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The marker profile, production of cytokine and chemokine, and antigen-presenting capability were studied to clarify the origin of tumor-infiltrating macrophages(TIM). Our results clearly showed that TIM was the hetrogeneous cell population having both capabilities of tumor-suppressing(M1) macrophage and tumor-promoting(M2) macrophages. On the other hand, the treatment of TIM with GM-CSF and siRNA for M-CSF induced the intra-cellular signal transducing molecules such as STAT-1, STAT-5, and STAT-6 of which are necessary for maturation toward antigen-presenting dendritic cells, nevertheless the maker-profiles of treated TIM did not change significantly. However both of the GM-CSF and siRNA for M-CSFR treated and non-treated TIM revealed similar antigen presenting capabilities in the system using OVA-specific TCR transgenic mice. Altogether it was clarified that the phenotype of TIM was reflecting the invading tumor microenvironment, and not certain cell type such as myeloid-derived suppressor cells, but was the cell that still keeped plasticity and could be changed by surrounding microenvironment.