Faulk W P, Galbraith G M
Proc R Soc Lond B Biol Sci. 1979 Mar 26;204(1154):83-97. doi: 10.1098/rspb.1979.0014.
Transferrin and specific transferrin receptors are demonstrated on the microvillous surface of syncytiotrophoblast in human immature and term placentae by immuno histological techniques with the use of light and electron microscopy. That the distribution of transferrin is limited to the materno-foetal interface supports the hypothesis that binding of maternal transferrin to trophoblast receptors is involved in the process of iron transport to the foetus. Parallel studies with baboon placentae demonstrate the presence of trophoblast receptors which bind both baboon and human transferrin, thereby putting forward an experimental model which might be used to test the biological significance of placental transferrin receptors in primates. In addition, investigation of a large number of human cell lines shows that many transformed cells, but no normal cells (such as blood lymphocytes) or cells from primary culture (such as neonatal foreskin fibroblasts), possess the ability to bind transferrin to their membranes. These findings suggest that transferrin receptors may play important biological roles in addition to that of iron transport from mother to foetus. One such role could be the limitation of iron in intervillous spaces, thus depriving iron-requiring microorganisms of iron, hence serving as a non-specific factor of resistance for placentae. Another role for foetal transferrin receptors on trophoblasts could be to bind maternal transferrin at the materno-foetal interface, thus frustrating maternal immunosurveillance. This is similar to a mechahism used by schistosomes in the host-parasite relation where host proteins are bound by the parasite to escape immunological recognition. The presence of transferrin receptors on transformed cells suggests that this mechanism might also be employed by tumour cells. Finally, in view of previous studies which show that transferrin is required by stimulated lymphocytes to pass from the G1 to the S phase of cellular replication, it is proposed that trophoblast transferrin receptors could limit the amount of transferrin in intervillous spaces and thus impede the proliferation and possible cytotoxicity of maternal activated lymphocytes at the materno-foetal interface.
运用光镜和电镜免疫组织学技术，在人类未成熟胎盘和足月胎盘的合体滋养层微绒毛表面证实了转铁蛋白和特异性转铁蛋白受体的存在。转铁蛋白的分布局限于母胎界面，这支持了以下假说：母体转铁蛋白与滋养层受体的结合参与了铁向胎儿转运的过程。对狒狒胎盘的平行研究表明，存在能结合狒狒和人类转铁蛋白的滋养层受体，从而提出了一个可用于测试灵长类动物胎盘转铁蛋白受体生物学意义的实验模型。此外，对大量人类细胞系的研究表明，许多转化细胞，但正常细胞（如血液淋巴细胞）或原代培养细胞（如新生儿包皮成纤维细胞）不具备将转铁蛋白结合到其膜上的能力。这些发现表明，转铁蛋白受体除了在铁从母体向胎儿转运中发挥作用外，可能还起着重要的生物学作用。其中一个作用可能是限制绒毛间隙中的铁，从而使需要铁的微生物得不到铁，因此成为胎盘的一种非特异性抵抗因素。滋养层上胎儿转铁蛋白受体的另一个作用可能是在母胎界面结合母体转铁蛋白，从而挫败母体的免疫监视。这类似于血吸虫在宿主 - 寄生虫关系中所采用的机制，即寄生虫结合宿主蛋白以逃避免疫识别。转化细胞上转铁蛋白受体的存在表明肿瘤细胞可能也采用了这种机制。最后，鉴于先前的研究表明，受刺激的淋巴细胞从细胞复制的G1期进入S期需要转铁蛋白，有人提出滋养层转铁蛋白受体可能会限制绒毛间隙中转铁蛋白的量，从而阻碍母体活化淋巴细胞在母胎界面的增殖及可能的细胞毒性。
