Roberts D M, Guenthert M, Rodewald R
Department of Biology, University of Virginia, Charlottesville 22901.
J Cell Biol. 1990 Nov;111(5 Pt 1):1867-76. doi: 10.1083/jcb.111.5.1867.
The yolk sac of the fetal rat and the proximal small intestine of the neonatal rat selectively transport maternal IgG. IgG-Fc receptors are thought to mediate transport across the epithelium of both tissues. We used a mouse mAb (MC-39) against the 45-54-kD component of the Fc receptor of the neonatal intestine to find an antigenically related protein that might function as an Fc receptor in fetal yolk sac. In immunoblots of yolk sac, MC-39 recognized a protein band with apparent molecular mass of 54-58 kD. MC-39 bound to the endoderm of yolk sac in immunofluorescence studies. In immunogold-labeling experiments MC-39 was associated mainly with small vesicles in the apical cytoplasm and in the region near the basolateral membrane of endodermal cells. The MC-39 cross-reactive protein and beta 2-microglobulin, a component of the intestinal Fc receptor, were copurified from detergent-solubilized yolk sac by an affinity purification that selected for proteins which, like the intestinal receptor, bound to IgG at pH 6.0 and eluted at pH 8.0. In summary, the data suggest that we have isolated the Fc receptor of the yolk sac and that this receptor is structurally and functionally related to the Fc receptor of the neonatal intestine. An unexpected finding is that, unlike the intestinal receptor which binds maternal IgG on the apical cell surface, the yolk sac receptor appears to bind IgG only within apical compartments which we suggest represent the endosomal complex.
胎鼠的卵黄囊和新生鼠的近端小肠可选择性转运母体IgG。IgG-Fc受体被认为介导了这两种组织上皮细胞的转运过程。我们使用一种针对新生鼠肠道Fc受体45 - 54 kD成分的小鼠单克隆抗体（MC - 39），来寻找一种在抗原上相关的蛋白质，它可能在胎鼠卵黄囊中作为Fc受体发挥作用。在卵黄囊的免疫印迹中，MC - 39识别出一条表观分子量为54 - 58 kD的蛋白条带。在免疫荧光研究中，MC - 39与卵黄囊的内胚层结合。在免疫金标记实验中，MC - 39主要与内胚层细胞顶端细胞质以及基底外侧膜附近区域的小泡相关联。通过亲和纯化从去污剂溶解的卵黄囊中共同纯化出MC - 39交叉反应蛋白和β2 -微球蛋白（肠道Fc受体的一个成分），该亲和纯化过程选择那些像肠道受体一样在pH 6.0时结合IgG并在pH 8.0时洗脱的蛋白质。总之，数据表明我们已经分离出卵黄囊的Fc受体，并且该受体在结构和功能上与新生鼠肠道的Fc受体相关。一个意外的发现是，与在顶端细胞表面结合母体IgG的肠道受体不同，卵黄囊受体似乎仅在我们认为代表内体复合物的顶端区室中结合IgG。
