The Role And Mechanism Of Myeloid-Derived Suppressor Cells In The Patients Of Multiple Sclerosis And Experimental Autoimmune Encephalomyelitis

BackgroundMultiple sclerosis (MS) is an autoimmune disease in the central nervous system (CNS) characterized by inflammation and demyelination in the white matter.Its precise etiology and pathogenesis remain enigmatic,so far there are no effective therapies to reverse the disease.Glucocorticoids are the main drug treatments for the acute episode and relapse of multiple sclerosis.Experimental autoimmune encephalomyelitis (EAE) is the classical animal model of MS, it provides very important experimental bases for this disease’s research.The first observations of myeloid-derived suppressor cells(MDSCs) were described in the patients with cancer.They are a heterogeneous population that is comprised of myeloid-cell progenitors and precursors of myeloid cells.Some pathological conditions result in an expansion of this population.These cells have a remarkable ability to suppress T-cell proliferation and regulate immune responses in the context of various diseases. Studies have shown that MDSCs abundantly accumulate within the peripheral blood and spleen of mice with experimental autoimmune encephalomyelitis at the onset of disease. However, to date, there are no systemic researches about the relationship between MDSCs and MS patients. Although, glucocorticoids have been shown to expand MDSCs in the murine models of trauma and skin allograft, little is known about the influence of glucocorticoids treatment on MDSCs in EAE models.Objective(1) To examine the changes and function of MDSCs in the peripheral blood of MS clinical patients in the active period and after glucocorticoids treatment.(2) To investigate the influence of glucocorticoids treatment on MDSCs in EAE model.(3)To find the differences of MDSCs researches between clinical studies in humans and animal models and then discuss the potential to target these cells for therapeutic benefit.Methods(1)Measuring the percentages of MDSCs and regulatory T cells (Treg cells)in the peripheral blood mononuclear cells (PBMC) of MS patients in the active period of this disease and after glucocorticoids treatment by flow cytometry.(2) Detecting the levels of serum Argl and iNOS in MS patients by specific Argl and iNOS test kits.(3)Detecting the suppressive activity of MDSCs in PBMC of MS patients by T cell proliferation assay.(4)C57BL/6 mice were immunized with 200ug MOG35-55 emulsified with Complete Freund’s Adjuvant (CFA).Pertussis toxin (PT) was intraperitoneally injected at 300 ng/permouse at day 0 and 2 post immunization.Furthermore, to make the glucocorticoids treatment model of EAE by injecting high-dose methylprednisolone intravenously.(5)The percentages of MDSCs and Treg cells in PBMC and the spleen cells of EAE mice in the active period of this disease and after glucocorticoids treatment were measured by flow cytometry.(6)The mRNA levels of Argl and Inos in the spleen of EAE mice were measured by qRT-PCR method.(7)To detect the suppressive activity of MDSCs in the spleen of EAE mice with glucocorticoids treatment and without it by T cell proliferation tests.Result(1)Compared with the healthy controls (HC),the percentages of MDSCs in PBMC of MS clinical patients did not increase in the active period of this disease. But, the percentages of G-MDSCs in PBMC from MS patients were significantly higher than those from the HC.(2)The percentages of MDSCs in PBMC from MS patients increased significantly after glucocorticoids treatments. The percentages of MDSCs in PBMC had significant differences between before and after glucocorticoids treatment (P<0.0001).(3)After glucocorticoids treatment, the percentages of M-MDSCs and G-MDSCs, two subpopulations of MDSCs,in PBMC from MS patients rised up. However,only the percentages of G-MDSCs in MDSCs significantly increased (P=0.0035)(4)The levels of serum Argl were higher in MS patients after glucocorticoids treatment and were positively correlated with the percentages of G-MDSCs in PBMC. Intracellular cytokine staining showed that G-MDSCs secreted the higher level of Argl than M-MDSCs.While glucocorticoids treatment did not change the level of serum iNOS.(5) After glucocorticoids treatment, the expanded MDSCs had obvious suppressive effect on T cell proliferation. But no significant difference of suppressive effect was detected between G-MDSCs and M-MDSCs.(6)After glucocorticoids treatment, the percentages of Treg cells in CD4+T cells of PBMC did not significantly change.(7)After the onset of EAE, mice were injected intravenously with high-dose methylprednisolone and glucocorticoids treatment could decrease the clinical scores of EAE, which mimiced successfully the clinical treatment condition of MS patients.(8)Compared with the naive mice, the percentages of MDSCs in PBMC and splenocytes of EAE mice significantly increased in the active period of this disease. Although no increase of MDSCs in PBMC of EAE mice, the percentages of G-MDSCs in MDSCs significantly increased after glucocorticoids treatment. This trend was consistent with that in PBMC of MS patients. In addition, the percentages of MDSCs and two subpopulations in the splenocytes of EAE mice did not significantly change after glucocorticoids treatment.(9)The mRNA levels of Argl and Inos in the spleen of EAE mice were significantly higher than the naive mice in the active period of this disease. No change was detected in the spleen of EAE mice after glucocorticoids treatment.(10)MDSCs from EAE mice with or without glucocorticoids treatment had obvious suppressive effect on T cell proliferation. M-MDSCs showed more strongly suppressive activity than G-MDSCs, and there was no significant difference of suppressive effect between MDSCs from EAE mice with or without glucocorticoids treatment.(11)Glucocorticoids treatment did not changed the percentages of Treg cells in CD4+T cells in PBMC and the spleen cells of EAE mice.Conclusion(1) The percentages of MDSCs in PBMC from MS patients do not increase in the active period of this disease.Glucocorticoids treatment expands MDSCs in PBMC.In addition, MDSCs secrete the higher level of Arg1 and show obvious suppressive effect on T cell proliferation after glucocorticoids treatment.(2) In the active period of this disease, the percentages of MDSCs in PBMC and the splenocytes of EAE mice significantly increase.The mRNA levels of Argl and Inos in the spleen of EAE mice are upregulated.Glucocorticoids treatment attenuates the development of this disease. However, the percentages of MDSCs and the mRNA levels of Arg1 and Inos have no significant changes after glucocorticoids treatment.(3)MDSCs from EAE mice suppress T cell proliferation, M-MDSCs show stronger suppression than G-MDSCs. But glucocorticoids treatment have no effect on suppressive activity.(4) EAE animal model can simulate successfully the clinical condition of MS patients, this trend is not completely consistent with that of MS patients at the aspects of MDSCs dynamics and function.