三碘甲状腺原氨酸对B细胞成熟分化的机制研究

Mechanisms of triiodothyronine on maturation and differentiation of B cells

目的三碘甲状腺原氨酸(T3)水平升高可促进B细胞成熟分化,浆细胞比例上升,但其机制尚不清楚。文章拟通过观察T3对小鼠骨髓,脾以及外周血B细胞活化因子(BAFF)水平和浆细胞比例的影响,探讨T3影响B细胞成熟分化的机制。方法将C57BL/6J鼠随机数字表法分为对照组(n=30)和T3组(n=50),分别用等渗盐水和T3 5μg/10g体重,1次/d,连续皮下注射6周,记录干预前、后小鼠的体重,饮食及饮水量,6周后检测两组小鼠外周血T3水平。流式细胞术检测两组小鼠脾、骨髓以及外周血B220^+CD138^+浆细胞比例,并检测B细胞表达IgM、IgG和IgD的比例。对小鼠甲状腺、脾组织切片行HE染色;对小鼠脾进行免疫组化、Western blot及实时定量PCR研究,观察和检测两组小鼠脾单个核细胞BAFF表达差异;ELISA测定小鼠血浆BAFF水平;免疫组化观察小鼠甲状腺单个核细胞BAFF的表达。结果注射T3 6周后,T3组小鼠血浆T3水平、饮食、饮水均较对照组明显升高(P<0.01)。高T3对小鼠脾的影响:T3组小鼠脾单个核细胞BAFF的相对mRNA 以及蛋白表达(2.03±0.52、0.50±0.03)较对照组(1.06±0.19、0.05±0.01)升高(P<0.01);T3组小鼠较对照组小鼠脾重量、体积明显增大,白髓区明显增大,且出现白髓区融合。流式细胞仪检测显示,T3组小鼠脾浆细胞的数量以及B细胞中表达抗体比例[(3.92±1.55)%、(75.76±8.88)%]较对照组[(2.43±1.18)%、(65.26±8.38)%]增加(P<0.05)。高T3对小鼠脾的影响:T3组小鼠骨髓浆细胞比例[(8.48±3.62)%]以及抗体表达[(40.63±18.96)%]较对照组[(4.96±3.11)%、(22.89±7.32)%]明显增加(P<0.05);外周血浆细胞比例[(8.56±4.27)%]以及抗体表达[(76.15±9.44)%]较对照组[(14.70±4.76)%、(84.20±3.98)%]降低(P<0.05);T3组小鼠外周血BAFF水平[(7.61±1.72) pg/mL]较对照组[(5.98±0.78) pg/mL]明显升高(P<0.01)。高T3对小鼠甲状腺的影响:HE染色结果显示,T3组小鼠甲状腺出现滤泡上皮细胞融合,滤泡内甲状腺球蛋白染色变浅,提示甲状腺球蛋白含量降低。免疫组化结果显示,T3组小鼠甲状腺单个核细胞BAFF表达水平较对照组增加。结论 T3激活骨髓、脾、外周血及甲状腺单个核细胞BAFF表达,并诱导骨髓及脾B细胞的分化,引起甲状腺组织发生病理变化,在甲状腺自身免疫性疾病的发病中起重要作用。

Objective Higher expression of B-cell activating factor (BAFF) in patients with Graves’ disease can activate B cells and increase proportion of plasma cells. However, the mechanism is still unclear. This study aims to investigate the effects of T3 on the BAFF level and plasma cell ratio in bone marrow, spleen and peripheral blood of mice, and to explore the mechanism of T3 in affecting the mature and differentiation of B cells. Methods 80 C57BL/6J mice were randomly divided into control group and T3 group, and were given isotonic saline or T3 5/10μg once a day for 6 weeks, respectively. The levels of T3 in peripheral blood of each group were measured with ELISA. Flow cytometry was used to detect the proportion of B220^+CD138^+ plasma cells and IgM, IgG and IgD expression of B cells in the spleen, bone marrow and peripheral blood. Immunohistochemistry, Western blot and PCR were performed to determine the expression of BAFF in spleen and thyroid. ELISA was used to determine the expression of BAFF in peripheral blood. Results Compared with control group, the levels of T3 in peripheral blood, diet and drinking water in the T3 group were significantly increased after 6 weeks T3 intervention. The mRNA and protein expression of BAFF in spleen mononuclear cells of T3 group (2.03±0.52, 0.50±0.03) were higher than those in control group (1.06±0.19, 0.05±0.01)(P<0.01). HE staining showed that the white medulla in the spleen of the T3 group increased and merged. Flow cytometry indicated that the proportion of spleen plasma cells and antibody expression of B cells in T3 group [(3.92±1.55)%,(75.76±8.88)%] increased compared with control group [(2.43±1.18)%,(65.26±8.38)%](P<0.05);Proportion of bone marrow plasma cells [(8.48±3.62)%] and antibody expression [(40.63±18.96)%] in T3 group were significantly increased compared with control group [(4.96±3.11)%,(22.89±7.32)%](P<0.05);Peripheral plasma cell ratio [(8.56±4.27)%] and antibody expression [(76.15±9.44)%] were lower than those in control group [(14.70±4.76)%,(84.20±3.98)%](P<0.05);Compared with control group [(5.98±0.78) pg/mL], the BAFF level in peripheral blood increased [(7.61±1.72) pg/mL](P<0.01). Immunohistochemistry showed that the expression of BAFF increased in mononuclear cells of thyroid of the T3 group. Conclusion T3 could activate BAFF expression in bone marrow, spleen, peripheral blood and thyroid mononuclear cells, and induce differentiation of bone marrow and spleen B cells, thus causing pathological changes in thyroid tissue. Such mechanisms might play an important role in the pathogenesis of thyroid autoimmune diseases.