Krop I, Shaffer A L, Fearon D T, Schlissel M S
Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
J Immunol. 1996 Jul 1;157(1):48-56.
CD19, a B cell-specific transmembrane protein, is essential for murine B-1 cell development and T cell-dependent B cell immune responses. Whereas signaling by the human B cell Ag receptor can be modulated by CD19, less is known about the biochemical properties of murine CD19. We have used a novel rat mAb specific for murine CD19 to study the biochemical properties of the murine protein. We demonstrate that murine CD19 shares with human CD19 an association with complement receptor CD21 and CD81, tyrosine phosphorylation, binding of phosphatidylinositol-3 kinase, and synergistic signaling with membrane IgM. Murine CD19 is shown also to enhance signaling through the micro-surrogate light chain complex of primary pre-B cells. We found that although expressed in the earliest B cell precursors, CD19 ligation does not activate Ca2+ mobilization until the pre-B cell stage of development. In mature B cells, CD19 cross-linking activates Ca2+ flux in B-2 cells but not in B-1 cells, although it can synergize with surface IgM in both B-1 and B-2 cells. These biochemical properties of CD19 will be important for understanding its function in B cell development and the humoral immune response.
CD19是一种B细胞特异性跨膜蛋白，对小鼠B-1细胞发育和T细胞依赖性B细胞免疫反应至关重要。虽然人B细胞抗原受体的信号传导可受CD19调节，但对小鼠CD19的生化特性了解较少。我们使用了一种针对小鼠CD19的新型大鼠单克隆抗体来研究该小鼠蛋白的生化特性。我们证明，小鼠CD19与人CD19一样，与补体受体CD21和CD81相关联、发生酪氨酸磷酸化、结合磷脂酰肌醇-3激酶，并与膜IgM协同信号传导。还显示小鼠CD19可增强通过原代前B细胞微替代轻链复合物的信号传导。我们发现，尽管CD19在最早的B细胞前体中表达，但直到发育的前B细胞阶段，CD19的连接才会激活Ca2+动员。在成熟B细胞中，CD19交联可激活B-2细胞中的Ca2+通量，但不能激活B-1细胞中的Ca2+通量，尽管它在B-1和B-2细胞中均可与表面IgM协同作用。CD19的这些生化特性对于理解其在B细胞发育和体液免疫反应中的功能将具有重要意义。
