van Noesel C J, Lankester A C, van Schijndel G M, van Lier R A
Department of Clinical Viro-Immunology, Central Laboratory of The Netherlands Red Cross Blood Transfusion Service, Amsterdam.
Int Immunol. 1993 Jul;5(7):699-705. doi: 10.1093/intimm/5.7.699.
The complement receptor 2 (CR2 or CD21) can be found in non-covalent association with the B lymphocyte specific CD19 complex at the surface of mature human B cells. Upon ligation of the B cell antigen receptor complex (BCR), members of the CR2-CD19 complex may associate with membrane immunoglobulin (mlg). Moreover, CD19 and CD21 ligands, either murine mAb, C3d fragments or Epstein-Barr virus, are known to have profound effects on B cell activation. We here show that CD19 is tightly linked to the non-receptor src kinase Lyn and that the CD19 glycoprotein itself serves as a substrate for a yet undefined serine/threonine kinase present within the complex. In the process of antigen recognition, mlg and the CR2-CD19 complex may bind different sites of a complement-opsonized antigenic particle. We hypothesize that in this process, approximation to the BCR allows CD19-associated Lyn kinase to phosphorylate potential substrates within the antigen-receptor complex, thereby effecting its coupling to the intracellular compartment.
补体受体2（CR2或CD21）可在成熟人类B细胞表面与B淋巴细胞特异性CD19复合物非共价结合。在B细胞抗原受体复合物（BCR）发生连接时，CR2-CD19复合物的成员可能与膜免疫球蛋白（mlg）结合。此外，已知CD19和CD21的配体，无论是鼠单克隆抗体、C3d片段还是爱泼斯坦-巴尔病毒，对B细胞活化都有深远影响。我们在此表明，CD19与非受体src激酶Lyn紧密相连，并且CD19糖蛋白本身是复合物中一种尚未明确的丝氨酸/苏氨酸激酶的底物。在抗原识别过程中，mlg和CR2-CD19复合物可能结合补体调理的抗原颗粒的不同位点。我们推测，在此过程中接近BCR可使与CD19相关的Lyn激酶磷酸化抗原受体复合物内的潜在底物，从而实现其与细胞内区室的偶联。
