Boackle S A, Morris M A, Holers V M, Karp D R
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262, USA.
J Immunol. 1998 Dec 15;161(12):6537-43.
Complement receptor 2 (CD21, CR2) is a B cell receptor for complement degradation products bound to Ag or immune complexes. The role of CD21 in mediating Ag presentation of soluble immune complexes by resting B cells was studied. Complement-coated immune complexes were formed by the incubation of influenza virus with serum from immune donors. These complexes bound to peripheral blood B cells in a complement-dependent manner. The binding required CD21 or, to a lesser extent, complement receptor 1 (CR1, CD35). B cells pulsed with immune complexes containing complement elicited a response from a panel of influenza-specific T cell clones, while those pulsed with immune complexes formed in the absence of complement did not. The expression of the early activation marker CD69 and the costimulatory molecule CD86 were not induced by CD21 ligation alone, suggesting that CD21-mediated Ag presentation occurs independently of B cell activation. Up-regulation of these markers required exposure to T cell factors elicited by the recognition of Ag derived from complement-containing immune complexes. These findings suggest that binding of Ag to CD21 enables Ag-nonspecific B cells to participate in the activation of Ag-specific T cells in a process that occurs independently of well-characterized B cell activation events.
补体受体2（CD21，CR2）是一种针对与抗原或免疫复合物结合的补体降解产物的B细胞受体。研究了CD21在静息B细胞介导可溶性免疫复合物的抗原呈递中的作用。通过将流感病毒与免疫供体的血清孵育形成补体包被的免疫复合物。这些复合物以补体依赖的方式与外周血B细胞结合。这种结合需要CD21，或者在较小程度上需要补体受体1（CR1，CD35）。用含有补体的免疫复合物脉冲处理的B细胞引发了一组流感特异性T细胞克隆的反应，而用在无补体情况下形成的免疫复合物脉冲处理的B细胞则没有。早期激活标志物CD69和共刺激分子CD86的表达不会仅由CD21连接诱导，这表明CD21介导的抗原呈递独立于B细胞激活而发生。这些标志物的上调需要暴露于由识别含补体免疫复合物衍生的抗原所引发的T细胞因子。这些发现表明，抗原与CD21的结合使抗原非特异性B细胞能够在一个独立于已充分表征的B细胞激活事件的过程中参与抗原特异性T细胞的激活。
