Characterization of a novel Fc gamma receptor-defined, IgG-containing organelle in human placental endothelial cells

人胎盘中的免疫球蛋白从母体循环转移到胎儿的循环中对胎儿和新生儿的免疫至关重要。这一过程需要免疫球蛋白穿透胎盘的两个细胞层。第一层合体滋养层的免疫球蛋白转运是由MHC相关的免疫球蛋白Fc受体FcRN介导的。第二层是绒毛内皮细胞，直到最近才被认为是通过小窝中的结构性细胞穿透来允许免疫球蛋白非特异性地移动。最近，研究表明绒毛内皮细胞表达一种独立的免疫球蛋白Fc受体，即巨噬细胞和B细胞上的FcγRIIb抑制基序。我们用超高分辨率免疫荧光和免疫电子显微镜表征了人胎儿内皮细胞中含有Fc、γ、RIIb的隔室。这些FcγRIIb细胞器中约有一半含有免疫球蛋白，其余的没有免疫球蛋白。大部分含Ig G细胞器(~80%)与FcγRIIb有关。没有含免疫球蛋白的细胞器与…相关更多的是洞穴。这些发现与FcγRIIb介导的免疫球蛋白在胎儿内皮细胞中的转移是一致的，独立于小凹。接下来，我们验证了FcγRIIb在胎盘内皮细胞中的表达，并通过逆转录聚合酶链式反应和测序分析确定了表达的FCGR2BmRNA转录变异体。FCGR2BmRNA序列在内皮细胞中特异表达，为转录变异体2序列。此外，对绒毛内皮细胞进行蛋白质组学和微阵列分析，发现可能与FcγRIIb囊泡相关的候选蛋白。这些蛋白在免疫球蛋白跨细胞途径中的进一步功能特征仍有待阐明。此外，人胎盘微绒毛合体滋养层细胞的蛋白质组学筛查显示，与某些肌营养不良相关的质膜修复蛋白--deferlin的表达。我们在绒毛内皮细胞中发现了一种新的FcγRIIb定义的、含有Ig G的细胞器，与小凹无关。这个细胞器可能是人胎盘中免疫球蛋白跨细胞的关键结构。较少

Human placental transfer of IgG from maternal circulation to that of the fetus is crucial for fetal and newborn immunity. This process requires that IgG broach two cellular layers of the placenta. IgG transport across the first layer, the syncytiotrophoblast, is mediated by the MHC-related Fc receptor for IgG, FcRn. The second layer, the villus endothelium, was until recently thought to allow IgG movement nonspecifically by constitutive transcytosis in caveolae. Recently, it has been shown that the villus endothelium expresses a separate Fc receptor for IgG, the inhibitory motif-bearing FcγRIIb seen on macrophages and B cells. We characterized the FcγRIIb-containing compartment in human fetal endothelial cells by ultrahigh-resolution immunofluorescence and immunoelectron microcopies. About half of these FcγRIIb organelles contain IgG; the remainder lack IgG. The majority fraction (~80%) of IgG containing organelles is associated with FcγRIIb. No IgG-containing organelles are associated … More with caveolin. These findings are compatible with FcγRIIb-mediated transfer of IgG across the fetal endothelial cells, independently of caveolae. Next, we verified the expression of FcγRIIb in the placental endothelial cells and use reverse transcriptase-polymerase chain reaction and sequencing analyses to define the expressed FCGR2B mRNA transcript variant. The mRNA sequence of FCGR2B expressed specifically in the endothelial cells is that of transcript variant 2. In addition, proteomics and microarray analyses of the villus endothelium discovered candidate proteins that were probably associated with FcγRIIb-vesicles. Further functional characterization of these proteins in the IgG-transcytosis pathway remains to be elucidated. In addition, a proteomics screen of human placental microvillous syncytiotrophoblast revealed the expression of dysferlin, a plasma membrane repair protein related with certain muscular dystrophies. We found a novel FcγRIIb-defined, IgG-containing organelle in the villus endothelium, unassociated with caveolae. This organelle is likely a key structure for the transcytosis of IgG in the human placenta. Less