抗原(Ag)触发的B细胞受体(BCR)信号传导启动抗体应答。然而,延长或不受控制的BCR信号与自身反应性B细胞和自身免疫性疾病的发展有关。我们先前表明,肌动蛋白介导的Ag呈递表面上的B细胞收缩负调节BCR信号传导。非肌肉肌球蛋白II(NMII),肌动蛋白马达,通过介导B细胞迁移参与B细胞发育和抗体反应,胞质分裂,和从Ag呈递细胞中提取Ag。然而,NMII是否以及如何通过BCR信号调节体液反应仍然难以捉摸。利用B细胞特异性,部分NMIIA基因敲除(cIAKO)小鼠模型和NMII抑制剂,这项研究探讨了NMII在BCR信号传导中的作用。当BCR与抗体包被的平面脂质双层(PLB)结合时,NMIIA被募集到B细胞接触膜并在B细胞收缩期间形成环状结构。NMII募集依赖于磷脂酰肌醇5-磷酸酶(SHIP1),一种抑制性信号分子.cIIKO抑制NMII不会影响B细胞在PLB上的扩散,但会延迟B细胞收缩并改变BCR聚类。可溶性刺激诱导的表面BCR“帽”形成在cIAKOB细胞中增强。值得注意的是,通过cIIKO和抑制剂的NMII抑制上调BCR信号,以响应表面相关和可溶性刺激,增加磷酸化酪氨酸,CD79a,BLNK,和Erk和减少磷酸化的SHIP1。虽然cIAKO不影响B细胞发育,生发中心B细胞的数量在未免疫的cIAKO小鼠中显著增加,与对照小鼠相比。虽然与免疫后的对照小鼠相比,cIAKO小鼠产生了相似的抗体反应,高亲和力抗体的百分比,cIAKO小鼠中Ag特异性生发中心B细胞和同种型转换B细胞明显低于对照小鼠。此外,cIAKO小鼠自身抗体水平升高,与对照小鼠相比。总的来说,我们的结果表明,NMII通过调节B细胞膜收缩和表面BCR聚集对BCR信号发挥B细胞内在抑制作用,抑制非特异性和自身反应性B细胞的激活。
Antigen (Ag)-triggered B-cell receptor (BCR) signaling initiates antibody responses. However, prolonged or uncontrolled BCR signaling is associated with the development of self-reactive B-cells and autoimmune diseases. We previously showed that actin-mediated B-cell contraction on Ag-presenting surfaces negatively regulates BCR signaling. Non-muscle myosin II (NMII), an actin motor, is involved in B-cell development and antibody responses by mediating B-cell migration, cytokinesis, and Ag extraction from Ag-presenting cells. However, whether and how NMII regulates humoral responses through BCR signaling remains elusive. Utilizing a B-cell-specific, partial NMIIA knockout (cIIAKO) mouse model and NMII inhibitors, this study examined the role of NMII in BCR signaling. Upon BCR binding to antibody-coated planar lipid bilayers (PLB), NMIIA was recruited to the B-cell contact membrane and formed a ring-like structure during B-cell contraction. NMII recruitment depended on phosphatidylinositol 5-phosphatase (SHIP1), an inhibitory signaling molecule. NMII inhibition by cIIAKO did not affect B-cell spreading on PLB but delayed B-cell contraction and altered BCR clustering. Surface BCR \"cap\" formation induced by soluble stimulation was enhanced in cIIAKO B-cells. Notably, NMII inhibition by cIIAKO and inhibitors up-regulated BCR signaling in response to both surface-associated and soluble stimulation, increasing phosphorylated tyrosine, CD79a, BLNK, and Erk and decreasing phosphorylated SHIP1. While cIIAKO did not affect B-cell development, the number of germinal center B-cells was significantly increased in unimmunized cIIAKO mice, compared to control mice. While cIIAKO mice mounted similar antibody responses when compared to control mice upon immunization, the percentages of high-affinity antibodies, Ag-specific germinal center B-cells and isotype switched B-cells were significantly lower in cIIAKO mice than in control mice. Furthermore, autoantibody levels were elevated in cIIAKO mice, compared to control mice. Collectively, our results reveal that NMII exerts a B-cell-intrinsic inhibition on BCR signaling by regulating B-cell membrane contraction and surface BCR clustering, which curtails the activation of non-specific and self-reactive B-cells.