Th17 Cell Roles In Pathogenesis Of Myasthenia Gravis

Myasthenia gravis(MG) and its animal model experimental autoimmune myasthenia gravis(EAMG) are autoantibodies mediated diseases of neuromuscular junctions.The nicotinic Acetylcholine receptors(AChR) at the postsynaptic membrane of neuromuscular junction are primary target for autoantibody attack in the majority of MG patients.Production of these antibodies in MG and EAMG are dependent of the cytokines produced by T helper (Th) cells.In order to understand the newly defined Th-17 cells in MG,we have used EAMG model as well as thymoma tissues from MG patients.Cellular immunology and genetic approaches in the thesis work have been combined.Autoreactive Th-17 cells drives pathogenic antibody production in EAMG have been identified.Further,IL-17 is highly expressed in thymoma tissues from patients with MG.Overal,these results reveal that IL-17 as a critical player for manifestation of muscular weakness and may serve as a target for novel immuno-therapy.Since differentiation of na(?)ve T cells into Th subtype requires interactions between innate and adaptive immune system prior to T cell activation.We first examined a chemokine CCL2(CC chemokine ligand 2,also named monocyte chemoattractantprotein 1,MCP-1) in development of EAMG.CCL2 expression was elevated in C57BL/6(B6) mice in lymph nodes and in spleen.CCL2-deficient(CCL2^-/-) mice is resistant to the development of EAMG. The level of serum anti AChR IgG,IgG1 and IgG2a in CCL2^-/-mice is similar to that of B6 mice,but IgG2b level is significantly reduced,indicating the possible reason of the resistance of CCL2^-/- mice to the development of EAMG is the reduced IgG2b level.CCL2 deficiency does not impair the capacity of B cells to proliferate,differentiate into plasma cells,release IgG antibodies and migration to the secondary lymphoid organs,the number of CD4⁺T cells that secretes IFN-γ(Th1 cell) and IL-4(Th2 cell) in CCL2 mice is slightly less than that of B6 mice,but the number of CD4⁺T cells that secretes IL-17 cells is significantly reduced in CCL2^-/- mice than that of B6 mice,implicating that reduced express of IgG2b in CCL2 mice is related with the reduced Th17 cells,implicating that reduced express of IgG2b in CCL2 mice is related with the reduced Th17 cells.The results show the role of CCL2 in the development fo EAMG,that is CCL2 drives Th17 cells priming,which assist B cells to produce pathological anit-AChR IgG2b,thus induce the functional blockage of neuromuscular junction(NMJ) and cause EAMG.Subsequent investigation reveals that lack of CCL2 lead impared homing of IL-6 producing CD11b⁺ monocytes.Subsequently,differentiation of AChR-reactive Th17 cells compromised.Thus,The results revealed CCL2 recruited IL-6 producing monocyte drive Th17 cells.The resistance to EAMG in IL-6^-/- mice could derive from faulty development of Th17 cells secondary to IL-6 deficiency.This result indicates a role of IL-6 in the development of AChR-specific Th17 cells in vivo,which induces the development of EAMG.The role of IL-17 in the development of EAMG was further examined by direct injecting of IL-17 to EAMG mice.Exogenous administration of IL-17 to B6 mice EAMG model showed severe signs and specific anti AChR IgG2b level was marked elevated,as indicated by a lack of disease induction in IL-17-deficient mice.Treatment of IFN-γ^-/- mice with IL-17 eaqully exacerbate EAMG,indicating that the role for IL-17 is independent of IFN-gamma. The RAG1^-/- recipient mice transferred AChR-specific Th17 cells from B6 mice developed EAMG suggests the role of Th17 cells in the development of EAMG as indicated by a lack of disease induction in IL-17 deficient mice.Given the associations of thymoma with MG,it was next exmianed whether IL-17 is present in thymoma.A retrospective analysis of 27 cases of thymoma for whom thymectomy were performed.The immunohistochemical staining with antibodies to CCL2,IL-17,IL-6, CD11b⁺ and CD4⁺ was performed on the parafine-embedded sections of the 27 thymoma specimen.Younger patients and male patients are easy to be complicated with MG.B1 and B2 type thymoma were more likely to accompanied with MG,while the C-type(malignant tumor) has a very small possibility to do that.The more benign thymoma was,the easier MG occurred,and the possibility was high for lymphocytes thymoma to be accompanied by MG. CCL2,IL-6 and IL-17 cytokines,CD11b⁺ cells and CD4⁺ cells were over-expressed in thymoma tumor tissues in patients with MG accompanied by thymoma.Above all,this paper demonstrated that Inflammation and/or immunization recruits CD11b⁺ mononuclear phagocytes to lymph nodes,a phenomenon that depends on CCL2.In the lymph nodes,those antigen presenting cells present the autoantigen to Th0 cells and make IL-6,which polarizes the Th0 cells toward a Th17 phenotype.The Th17 cells are then required as helpers for the production of high titer of pathogenic anti-AChR IgG2b antibodies from B cells.Those antibodies are the ultimate responsible for the block at the neuromuscular junction that leads to muscular weakness.The role of Th17 cells in the development of EAMG is not dependent on Th1 cell.We show that CCL2 can facilitate the cognate interactions among IL-6-producing CD11b⁺ cells,autoreactive Th17 cells,and B cells.These interactions are critical in the genesis of autoantibodies and in the subsequent development of manifestations of diease.The evidence of that CCL2,IL-6 and IL-17 cytokines,CD11b⁺ cells and CD4⁺ cells were over-expressed in thymoma tumor tissues in patients with MG accompanied by thymoma.In the tumor tissues of thymoma accompanied with MG supports our prediction:Th17 cells have a role in B cell-mediated autoimmune diseases.In the tumor tissues of thymoma accompanied with MG,highly expressed IL-17 may also initiate the MG's autoimmune reactions.