Brandtzaeg P, Prydz H
Nature. 1984;311(5981):71-3. doi: 10.1038/311071a0.
J chain is a polypeptide of molecular weight (Mr) approximately 15,000 common to human dimeric IgA and pentameric IgM. These immunoglobulin polymers show a high affinity for secretory component (SC) in vitro, a feature that, in some studies, has been claimed to be a function of the J chain. SC is a glycoprotein of Mr approximately 80,000 which is expressed on the basolateral surfaces of secretory epithelial cells where, according to a current hypothesis, it may act as a receptor for dimeric IgA and pentameric IgM which are selectively transported through secretory epithelial cells into exocrine fluids. Previous studies, however, have not excluded the possibility that secretory cells express isotype-specific Fc receptors for IgA and IgM which may be involved in epithelial transport. We now report that the adsorption of immunoglobulin polymers to SC-expressing epithelial cells depends solely on a J chain-determined binding site. This finding lends biological significance to the striking J-chain expression shown by immunoglobulin-producing immunocytes in secretory tissues.
J链是一种分子量（Mr）约为15,000的多肽，存在于人类二聚体IgA和五聚体IgM中。这些免疫球蛋白聚合物在体外对分泌成分（SC）具有高亲和力，在一些研究中，这一特性被认为是J链的功能。SC是一种分子量约为80,000的糖蛋白，表达于分泌上皮细胞的基底外侧表面，根据目前的假说，它可能作为二聚体IgA和五聚体IgM的受体，这些聚合物通过分泌上皮细胞被选择性转运到外分泌液中。然而，先前的研究并未排除分泌细胞表达可能参与上皮转运的IgA和IgM同种型特异性Fc受体的可能性。我们现在报告，免疫球蛋白聚合物与表达SC的上皮细胞的吸附完全取决于由J链决定的结合位点。这一发现赋予了分泌组织中产生免疫球蛋白的免疫细胞所表现出的显著J链表达生物学意义。
