The Activation Mechanism Of F4/80~+CD11b~+Gr-1~+ Monocytes In Tumor Microenvironment

It is known that macrophage can inhibit tumor growth through cytokine production, and induce tumor cell apoptosis. There are many literatures showing that macrophage in tumor microenvironment is different from the normal macrophage in the phenotype, cytokine production and function. Macrophage is known derived from bone marrow precursors with a phenotype of F4/80+Gr-1+, and plays an important role in tumor growth and metastasis. However, the mechanism of how macrophages are activated and how they interact with tumor cells is not clear yet.We notice that tumor associate macrophage can promote tumor cells growth, which is independent of direct interaction of macrophage and tumor cells. However, this effect depends on the exposure of macrophage to huge amount of tumor cells, so we speculate it is the function of molecules released from necrosis tumor cells on macrophage. We use molecules from necrotic tumor cell (NTC-Ms) as the model of tumor microenvironment to investigate the mechanism of macrophage's function switch.Our results have shown that monocytes expressing F4/80+CDllb+from tumor tissue, bone marrow and peripheral blood also express Gr-1. We speculate that F4/80+CD11b+Gr-1+in tumor may be directly derived from bone marrow precursors. Moreover, NTC-Ms treated bone marrow precursors can develop an inhibit phenotype, which expressed Arginase 1, Inducible nitricoxide synthase, interleukin-10, interleukin-12 and inhibit CD4+and CD8+T cell's proliferation. All these have shown a functional switch of bone marrow derived F4/80+CD11b+Gr-1cells.We have found that N-BMDMs, T-BMDMs and F4/80+Gr-1+BMDMs expressed TLR2 and TLR4. Further research showed that NTC-Ms could activate IRF-3 rather than NF-κB, which indicate that NTC-Ms could regulate bone marrow development through IRF-3/TRIF pathway but not NF-κB-MyD88 pathway. By using resveratrol (a TLR4 agonist, which can block TRIF pathway) to treat bone marrow precursors together with NTC-Ms, the up-regulation of Arg1,Nos2,IL-10 and IL-12 induced by NTC-Ms and CD4+CD8+T cell apoptosis were largely inhibited. We try to figure out the effective component in NTC-Ms, and the result showed it is protein not RNA in NTC-Ms can start the TLR4 signal transduction.Our previous study had shown that IFN-γis an important factor in inhibiting tumor invasion. We further showed that IFN-γis also important for bone marrow precursor's activation through TLR4 pathway. In this experiment, results showed that IFN-γcould inhibit BMDM induced T cell apoptosis as well as tumor growth and metastasis. But as the tumor development, the sensitivety of T-BMDM to IFN-γis down-regulated. Another observation here is that IL-10 can down regulate Nos2 and IL-12 secretion by N-BMDMs when they were treated with NTC-Ms. On top of that, IFN-γcan activate STAT-1 while IL-10 can activate STAT-3, which indicates IFN-γand IL-10 might work through JAK/STAT pathway in inducing CD4+and CD8+T cell apoptosis, down regulating Nos2 and IL-12 expression, making macrophage into M2 phenotype so that the tumor cells could escape from the innate immunity.All in all, we investigate the influence of tumor microenvironment on F4/80+Gr-1+cells, how they develop in tumor bearing organism and the possible pathway involved. This study would also provide scientific rational for the next step of target immune therapy.