The neonatal Fc receptor (FcRn) was first recognized for its role in transfer of maternal IgG to the foetus or newborn, providing passive immunity early in life. However, it has become clear that the receptor is versatile, widely expressed and plays an indispensable role in both immunological and non‐immunological processes throughout life. The receptor rescues immunoglobulin G (IgG) and albumin from intracellular degradation and shuttles the ligands across polarized cell barriers, in all cases via a pH‐dependent binding‐and‐release mechanism. These processes secure distribution and high levels of both IgG and albumin throughout the body. At mucosal sites, FcRn transports IgG across polarized epithelial cells where it retrieves IgG in complex with luminal antigens that is delivered to tissue‐localized immune cells. In dendritic cells (DCs), FcRn orchestrates processing of IgG‐opsonized immune complexes (ICs) in concert with classical Fcγ receptors, which results in antigen presentation and cross‐presentation of antigenic peptides on MHC class II and I to CD4+ and CD8+ T cells, respectively. Hence, FcRn regulates transport of the ligands within and across different types of cells, but also processing of IgG‐ICs by immune cells. As such, the receptor is involved in immune surveillance and protection against infections. In this brief review, we highlight how FcRn expressed by hematopoietic and non‐hematopoietic cells contributes to immune regulation at mucosal barriers—biology that can be utilized in development of biologics and subunit vaccines for non‐invasive delivery.

中文翻译：

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新生儿Fc受体在黏膜免疫调节中的作用

新生儿Fc受体（FcRn）因其在将母体IgG转移至胎儿或新生儿中的作用而首次被认可，可在生命早期提供被动免疫。然而，很明显，该受体是一类通用的，广泛表达的，并且在一生中都在免疫和非免疫过程中起着不可或缺的作用。在所有情况下，该受体均可通过pH依赖的结合和释放机制从细胞内降解中拯救免疫球蛋白G（IgG）和白蛋白，并使配体跨过极化的细胞屏障。这些过程确保了IgG和白蛋白在体内的分布和高水平。在粘膜部位，FcRn跨极化的上皮细胞转运IgG，在那里它与管腔抗原复合地回收IgG，然后将其输送到组织定位的免疫细胞中。在树突状细胞（DC）中 FcRn协同经典的Fcγ受体协调IgG调理免疫复合物（IC）的加工，从而导致抗原呈递和抗原肽在MHC II类和I类上的交叉呈递分​​别呈递给CD4 +和CD8 + T细胞。因此，FcRn调节配体在不同类型的细胞内和跨细胞的转运，还调节免疫细胞对IgG-IC的处理。这样，该受体参与免疫监视和针对感染的保护。在这篇简短的综述中，我们着重介绍造血细胞和非造血细胞表达的FcRn如何促进粘膜屏障的免疫调节-生物学可用于开发生物制剂和亚单位疫苗以进行非侵入性递送。这会导致抗原肽在MHC II类和I类上呈递和交叉呈递到CD4 +和CD8 + T细胞。因此，FcRn调节配体在不同类型的细胞内和跨细胞的转运，还调节免疫细胞对IgG-IC的处理。这样，该受体参与免疫监视和针对感染的保护。在这篇简短的综述中，我们着重介绍造血细胞和非造血细胞表达的FcRn如何促进粘膜屏障的免疫调节-生物学可用于开发生物制剂和亚单位疫苗以进行非侵入性递送。这会导致抗原肽在MHC II类和I类上呈递和交叉呈递到CD4 +和CD8 + T细胞。因此，FcRn调节配体在不同类型的细胞内和跨细胞的转运，还调节免疫细胞对IgG-IC的处理。这样，该受体参与免疫监视和针对感染的保护。在这篇简短的综述中，我们着重介绍造血细胞和非造血细胞表达的FcRn如何促进粘膜屏障的免疫调节-生物学可用于开发生物制剂和亚单位疫苗以进行非侵入性递送。而且还可以通过免疫细胞处理IgG-IC。这样，该受体参与免疫监视和针对感染的保护。在这篇简短的综述中，我们着重介绍造血细胞和非造血细胞表达的FcRn如何促进粘膜屏障的免疫调节-生物学可用于开发生物制剂和亚单位疫苗以进行非侵入性递送。而且还可以通过免疫细胞处理IgG-IC。这样，该受体参与免疫监视和针对感染的保护。在这篇简短的综述中，我们着重介绍造血细胞和非造血细胞表达的FcRn如何促进粘膜屏障的免疫调节-生物学可用于开发生物制剂和亚单位疫苗以进行非侵入性递送。