Schiff J M, Underdown B J
FEBS Lett. 1985 Mar 11;182(1):85-9. doi: 10.1016/0014-5793(85)81159-5.
The rat and rabbit transport IgA from blood to bile by a highly efficient transcellular pathway mediated by secretory component (SC). Other mammals do not express SC on liver hepatocytes, but they do transport a small amount of IgA to bile. In the first part of this study, human polymeric IgA was radiolabeled and depleted of SC binding activity by successive affinity adsorption. Transport of this preparation intact to rat bile was 4%, but was reduced to 2% when 50 mg unlabeled asialoglycoprotein was preadministered. The 2% decline corresponds to the percent of asialo-orosomucoid diverted to bile from the lysosomal pathway. In guinea-pigs, missorting of asialo-orosomucoid intact to bile was 10% of the injected dose. Transport of normal human IgA to bile was 1-2%, even though guinea-pigs do not express SC in the liver. Excess unlabeled asialofetuin reduced the transport of asialo-orosomucoid by 10-fold and IgA by 6-fold. This demonstrates that the asialoglycoprotein receptor can mediate transport of IgA to bile in small amounts, but that this transport may be only a biological artifact resulting from limited fidelity of intracellular protein sorting.
大鼠和兔子通过由分泌成分（SC）介导的高效跨细胞途径将IgA从血液转运至胆汁。其他哺乳动物的肝脏肝细胞不表达SC，但它们确实会将少量IgA转运至胆汁。在本研究的第一部分，人聚合IgA经放射性标记，并通过连续亲和吸附去除SC结合活性。该制剂完整转运至大鼠胆汁的比例为4%，但预先给予50mg未标记的去唾液酸糖蛋白时，该比例降至2%。这2%的下降对应于从溶酶体途径转向胆汁的去唾液酸血清类黏蛋白的百分比。在豚鼠中，完整的去唾液酸血清类黏蛋白误分选至胆汁的量为注射剂量的10%。正常人IgA向胆汁的转运率为1%-2%，尽管豚鼠肝脏中不表达SC。过量的未标记去唾液酸胎球蛋白使去唾液酸血清类黏蛋白的转运减少了10倍，使IgA的转运减少了6倍。这表明去唾液酸糖蛋白受体可介导少量IgA向胆汁的转运，但这种转运可能只是细胞内蛋白质分选保真度有限导致的生物学假象。
