Tomana M, Kulhavy R, Mestecky J
Division of Clinical Immunology and Rheumatology, University of Alabama, Birmingham.
Gastroenterology. 1988 Mar;94(3):762-70. doi: 10.1016/0016-5085(88)90252-1.
We have studied the molecular mechanisms of the binding and uptake of secretory and serum immunoglobulin A (IgA) of both subclasses (1 and 2) and molecular forms (monomer and polymer) by the particulate fraction of human liver homogenate and by a human hepatoma cell line (HepG2). Inhibition by asialoorosomucoid and the requirement for the presence of calcium indicated that the binding of secretory IgA and polymeric IgA1 was mediated by the asialoglycoprotein receptor. Secretory component, which functions as a receptor for polymeric IgA in several animal species, was detected in the epithelial cells of bile ducts, but not in hepatocytes. Secretory IgA and all molecular forms and subclasses of serum IgA were bound by HepG2 cells, which do not express secretory component. The requirement for the presence of calcium, the presence of a terminal galactose residue in IgA, and the molecular weight of the major plasma membrane protein responsible for binding (41,700 daltons) indicated the involvement of asialoglycoprotein receptor. Immunoglobulin A proteins bound by HepG2 cells were endocytosed and catabolized.
我们研究了人肝匀浆微粒部分和人肝癌细胞系（HepG2）对分泌型和血清免疫球蛋白A（IgA）两个亚类（1和2）以及分子形式（单体和聚合物）的结合和摄取的分子机制。去唾液酸糖蛋白抑制以及对钙存在的需求表明，分泌型IgA和聚合型IgA1的结合是由去唾液酸糖蛋白受体介导的。分泌成分在几种动物物种中作为聚合型IgA的受体发挥作用，在胆管上皮细胞中被检测到，但在肝细胞中未被检测到。分泌型IgA以及血清IgA的所有分子形式和亚类都被不表达分泌成分的HepG2细胞结合。对钙存在的需求、IgA中末端半乳糖残基的存在以及负责结合的主要质膜蛋白的分子量（41,700道尔顿）表明去唾液酸糖蛋白受体参与其中。HepG2细胞结合的免疫球蛋白A蛋白被内吞并分解代谢。
