| Objective Systemic lupus erythematosus(SLE)is a chronic autoimmune disease with heterogeneous inflammation.It is characterized as the absence of immune tolerance to autoantigens,continuous production of pathogenic autoantibodies,formation of immune complexes deposited in various organs,resulting in multiple organs injury,including nervous system,kidney and lung.Neuropsychiatric lupus erythematosus(NPSLE)is one of the most serious complications with high mortality.Lupus nephritis(LN)is not only the most common complication but also one of the most common causes of death in SLE patients.The abnormal activation of T and B-lymphocytes and the disorder of multiple regulatory networks that down regulate these immune responses play an important role in SLE.Increasing evidences show that the deficiency of function or loss of number in Treg cells can lead to the increase of Th17 cell activity in SLE.Brain-derived neurotrophic factor(BDNF)plays an important role in promoting the growth,differentiation and survival of neurons.In addition,recently,BDNF was also reported to exist in peripheral blood,and lymphocyte was one of the main sources of BDNF and expressed its specific receptor tyrosine kinase B(Trk B).BDNF can promote the proliferation of T cells and have anti-apoptosis role of T cells.Our aim in this study is to investigate serum BDNF level and Trk B expression on the surface of T lymphocytes in peripheral blood of SLE patients,to explore the potential relationship between BDNF and SLE,and whether BDNF is involved in the pathogenesis of SLE.Finally,we will probe into whether BDNF affects the proliferation and differentiation of CD4+ T cells into Treg and Th17 cells in SLE patients and regulates the immune function of T lymphocytes in SLE.Methods一、Peripheral blood brain-derived neurotrophic factor level and tyrosine kinase B expression on T lymphocytes in systemic lupus erythematosus:Implications for systemic involvement Samples from fifty SLE patients and thirty healthy controls were evaluated.Serum BDNF level was measured by enzyme-linked immunosorbent assay(ELISA)and percentages of Trk B expression on the surface of CD3+CD4+ and CD3+CD8+T lymphocytes were measured by flow cytometry.SLE patients were divided into subgroups according to whether they exhibited brain,kidney or lung involvement,and whether the disease was inactive or active.二、The study of BDNF on differentiation of Th17 and Treg cells in peripheral blood of patients with systemic lupus erythematosus and the mechanism Thirty SLE patients were recruited,and CD4+T lymphocytes were selected by magnetic beads from the patients and were divided into two groups.TGF-β,TGF-β+IL-6were added to make CD4+T cells differentiate into Treg and Th17 cells,and human recombinant BDNF protain of different concentrations(60ng/ml,120ng/ml,350ng/ml)were added into the two groups for 72 hours.Then the percentages of CD4+CD25+CD127low(Treg)cells and CD4+IL-17A+(Th17)cells were detected by flow cytometry,and the expression of Foxp3 m RNA and RORγtm RNA was detected by RT-PCR.Under the condition of Treg and Th17 cells polarization,BDNF(350ng/ml)and Trk B antagonists(Trk B Ig G)were added respectively.The phosphorylation of Akt、m TORC1 and ERK1/2 was detected by western blot,and the percentages of CD4+CD25+CD127low cells and CD4+IL-17A+ cells were detected by flow cytometry.Results一、Peripheral blood brain-derived neurotrophic factor level and tyrosine kinase B expression on T lymphocytes in systemic lupus erythematosus:Implications for systemic involvement Serum BDNF level in SLE patients was decreased when compared with the controls(p﹤0.001),and negative correlation was found between serum BDNF level and SLEDAI score(r =-0.619,P < 0.001).Comparing with the SLE patients without organ involvement,BDNF level was significantly lowerin SLE with LN(p=0.042)and in NPSLE group(p=0.04).BDNF level in inactive group was significantly higher(P﹤0.001)when compared with active SLE group.The percentages of Trk B expression on CD3+CD4+ and CD3+CD8+ T cell surface were significantly higher(p﹤0.001;p﹤0.001,respectively)than that in healthy controls.二、The study of BDNF on differentiation of Th17 and Treg cells in peripheral blood of patients with systemic lupus erythematosus and the mechanism Under the condition of Th17 cell polarization,the proportion of CD4+IL-17A+cells in each group gradually decreased(P<0.01)with the increase of BDNF concentration(60ng/ml,120ng/ml,350ng/ml),and the expression of RORγtm RNA in each group detected also decreased significantly(P<0.001).Under the condition of Treg cell polarization,with the increase of BDNF concentration(120ng/ml,350ng/ml),the proportion of CD4+CD25+CD127lowcells gradually increased(P<0.001),but not increased in 60ng/ml BDNF group,and the expression of Foxp3 m RNA in group also increased in each group(P<0.001).Under the condition of Th17 cell polarization,compared with the blank control group,the phosphorylation of Akt,m TORC1 and ERK1/2 by western blot in the high concentration of BDNF(350ng/ml)group decreased significantly(P < 0.001),the proportion of CD4+IL-17A+ cells also decreased.While there was no significant difference in Akt,m TORC1 and ERK1/2 phosphorylation in BDNF+Trk BIg G group,nor in the percentages of CD4+IL-17A+ cells detected by flow cytometry.Conclusions一、Serum BDNF level combined with Trk B expression on T cell surface can reflect disease activity in SLE.It is possible that BDNF may be used as a potential serological biomarker for disease activity of SLE.In addition,the significant decrease in serum BDNF level may imply organ involvement of SLE patients,as well as possibly differentiate NPSLE from hormone-induced mental disorders.二、BDNF inhibits the differentiation of Th17 cells and upregulates the differentiation of Treg cells in SLE patients through PI3K-Akt-m TORC1 axis,and plays a certain role to maintain the balance of Treg/Th17 lymphocytes.It may provide a brand new thought for the pathogenesis and treatment of SLE. |
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