Blocking TNFR Signaling Reduces The Recruitment And Migration Of MDSC To Tumor Tissue

Purpose: It was reported that there are a large number of immature myeloid cells in the tumor tissue and chronic inflammation, which was named myeloid-derived suppressor cells (MDSCs) because of their strong immune suppression. MDSCs are a phenotypically heterogeneous cell population that include mature myeloid cells, such as granulocytes, monocytes/macrophages, and dendritic cells (DCs), as well as immature myelo-monocytic precursors, and they use a diversity of mechamisms to suppress multiple immune effects. Recent studies have found that many inflammatory cytokines such as IL-1β, IL-6, PGE2, and S100A9 are involved in MDSC recruitment and migration in secondary immune organs, such as spleen and lymphoid nodes, and in tumor tissue. Tumor necrosis factor alpha (TNF-α) is a classic and initial inflammatory factor. It plays a dual role on tumor occurrence and development. However, it's not clear that the relationship between TNF-αand MDSC. The purpose of this research was to explore the effect of TNF-αon recruitment and immune suppression function of MDSC.Methods: Hepatoma cell lines H22 with BALB/c background were inoculated subcutaneously and respectively to wild type and TNFR1R2 double-deficient mice. Tumor size and survival status of tumor-bearing mice were observed dynamically. Flow cytometry + and / or immunohistochemistry were used to detect the percentage and distribution of Gr-1CD11b+ MDSC in bone marrow, spleen, peripheral blood and tumor tissue in tumor-bearingmice. Chemotaxis assay was used to test the chemotaxis ability of bone marrow-derivedMDSC to tumor tissue, RT-PCR methods and ELISA and / or Western-blotting were used todetect the expression levels of mRNA and protein of the inflammatory cytokines such asIL-1β, IFN-γand S100A9 in tumor tissue or MDSC themselves. At the same time, RT-PCRmethod was used to detect expression levels of iNOS and ARG1 mRNA in bonemarrow-derived MDSC of tumor-bearing mice. Inhibition assay of T cell proliferationstimulated by PMA and ionomycin was used to detect inhibition of MDSC on T cellresponseResults: Tumor was grown much significantly more slowly and survival time wasprolonged more in the TNFR1R2 double-deficient tumor-bearing mice than that of in thewild type of tumor-bearing mice(p<0.01). In 2-5 weekend point after inoculation of tumorcells, percentage of Gr-1+ CD11b+MDSC detected by flow cytometry in the spleen,peripheral blood and tumor tissue in TNFR1R2 double-deficient tumor-bearing mice wereall significantly less than that of in wild type tumor-bearing mice(p<0.01). Althoughincreasing with tumor growth, percentage of Gr-1+ CD11b+ MDSC in bone marrow was nosignificant difference between the two groups in later period of tumor growth(p>0.05).Chemotactic migration index of bone marrow-derived MDSC to tumor tissue, in TNFR1R2double-deficient tumor bearing- mice, was significantly lower than that of in wild type tumor tissue, and prolonged survival time of tumor-bearing mice. The mechanism of the lessening recruitment and migration of MDSC was possibly that TNFα-related inflammatory cytokines, such as IL-1βand S100A9 in MDSC itself and in tumor tissue were reduced by TNFR1R2 deletion. However, Blocking TNFR signaling did not TNFR1R2 double -deficient tumor-bearing mice were significantly lower than that in wild type tumor-bearing mice (p<0.01); The levels of protein expression of S100A9 both in MDSC themselves and in tumor tissues of TNFR1R2 double-deficient tumor-bearing mice were both significantly lower than that of in wild type tumor- bearing mice. The iNOS mRNA levels of MDSC of TNFR1R2 double-deficient tumor-bearing mice were significantly lower than that of in the wild type tumor-bearing mice, but the mRNA levels of ARG1 compared with wild type tumor-bearing mice was no significant change(p>0.05). Inhibition of MDSC on T cell proliferation was no significant differences between the TNFR1R2 double-deficient bearing-tumor mice and wild-type tumor- bearing mice(p>0.05) .Conclusion: Blocking TNFR signaling reduced recruitment and migration of MDSC to tumor-bearing mice(p<0.01). The levels of mRNA and protein of IL-1βin TNFR1R2 double -deficient tumor-bearing mice were significantly lower than that in wild-type tumor-bearing mice(p<0.01); while, the levels of mRNA and protein of IFN-γin seemingly effect immune suppression of MDSC on T cell proliferation, and this was maybe owe to increase of IFN-γexpression TNFR1R2 deletion.