Ling N R, Hardie D L, Johnson G D, MacLennan I C
Department of Immunology, University of Birmingham, UK.
Clin Exp Immunol. 1998 Sep;113(3):360-6. doi: 10.1046/j.1365-2249.1998.00668.x.
By analysis with a panel of CD21 MoAbs it is shown that a large part of the soluble CD21 in human blood plasma is of the long isoform (CD21L), as judged by comparison with antigen produced by mouse L cells transfected with CD21L-cDNA and reactivity with the restricted CD21 MoAb R4/23. This is compatible with the hypothesis that soluble CD21 in the blood is mainly derived from follicular dendritic cells (FDC). Cells from a human keratinocyte cell line transfected with cDNA from the Burkitt lymphoma cell line Raji also produced soluble CD21L (sCD21L), whereas the short form of sCD21 (sCD21S) was the major component of sCD21 produced by the B lymphoblastoid cell line LICR-LON-HMy and the T cell line Jurkat. Confocal studies of FDC isolated from human tonsil revealed that CD21 was present in the cytoplasm. On gel filtration sCD21 from untreated serum has an apparent size considerably greater than the 130kD found by SDS-PAGE analysis. This may be partly accounted for by the non-globular shape of the molecule, but may also indicate, as reported by others, that in its native state sCD21 is complexed with other proteins. However, no evidence of complexing with sCD23 or C3d could be found.
通过用一组CD21单克隆抗体进行分析表明，人血浆中大部分可溶性CD21是长异构体（CD21L），这是通过与用CD21L - cDNA转染的小鼠L细胞产生的抗原进行比较以及与限制性CD21单克隆抗体R4/23的反应性来判断的。这与血液中的可溶性CD21主要来源于滤泡树突状细胞（FDC）的假设相符。用人角质形成细胞系转染伯基特淋巴瘤细胞系Raji的cDNA后得到的细胞也产生可溶性CD21L（sCD21L），而B淋巴母细胞系LICR - LON - HMy和T细胞系Jurkat产生的可溶性CD21的主要成分是短形式的sCD21（sCD21S）。对从人扁桃体分离的FDC进行共聚焦研究发现，CD21存在于细胞质中。在凝胶过滤中，未经处理的血清中的sCD21的表观大小明显大于SDS - PAGE分析所发现的130kD。这可能部分是由于分子的非球状形状，但也可能如其他人所报道的那样，表明sCD21在其天然状态下与其他蛋白质复合。然而，未发现与sCD23或C3d复合的证据。
