RESUMO
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.
RESUMO
Objective High levels of triiodothyronine (T3) can lead to hyperthyroid heart disease, but its mechanism is unclear. This study aims to investigate the effects of T3 on the expression of B-cell activating factor (BAFF) in cardiomyocytes and to explore its possible role in the pathogenesis of hyperthyroid heart disease. Methods Sixty healthy C57BL/6J mice were selected and randomly divided into two groups: the experimental group and the control group. The experimental group received intraperitoneal injection of T3 at 5 μg/ml, one time/d, for 42 consecutive days. The concentrations of serum T3 and tetraiodothyronine (T4) were detected by radioimmunoassay; ELISA was used to determine BAFF expression in peripheral blood, and the cardiac index and the transverse diameter of myocardial cells in each group were determined. Immunohistochemistry and Western blot were used to detect the expression of BAFF protein in myocardium and of myocardial tumor necrosis factor-α (TNF-α) protein; the expression of BAFF mRNA in myocardium was detected by Real-Time PCR; flow cytometry (FCM) was used to detect changes in the proportion of B-cells in the heart. Results Compared with the control group, the serum T3 concentration, cardiac index, BAFF and myocardial cell transverse diameter of the experimental group significantly increased (P<0.05), and the T4 concentration decreased (P<0.05). Under the light microscope, the cardiomyocytes of the control group were normal, while those of the experimental group were hypertrophied and disordered in structure. Compared with the control group (0.765±0.164), BAFF protein expression significantly increased in the experimental group (1.865±0.290) (P<0.05). Compared with the control group (0.537±0.089), the expression of TNF-α protein significantly increased in the experimental group (0.737±0.065) (P<0.05). Correlation analysis of T3 with BAFF gene expression in cardiomyocytes and BAFF level in peripheral blood showed that T3 was positively correlated with both the former with a correlation coefficient of 0.637 (P<0.01) and the latter with 0.778 (P<0.01). For FCM, compared with the control group [(12.40±1.09)%], the proportion of myocardial B-cells increased in the experimental group [(16.12±0.631)%] (P<0.05). Conclusion High concentration of T3 can promote the expression of BAFF in myocardial cells and lead to the activation of B-cells, thus increasing the inflammatory response and leading to myocardial hypertrophy.