Fig 1.
IgG transfer from mother to offsprings.
(A) In neonatal rodents, maternal IgG is processed in the stomach and enters the duodenum (pH ~ 6.0). Here, IgG binds to FcRn on duodenal epithelial cells, which transports it across the cell via transcytosis and releases it into the basolateral space at physiological pH (7.4). (B) In humans, placental cells internalize maternal IgG. Acidification of endosomes (pH ~ 6.0) strengthens IgG-FcRn binding. Vesicles traffic to the fetal side, where neutral pH (7.4) triggers IgG release. The schematic, inspired by reference [14], was redrawn using BioRender.com.
Fig 2.
FcRn prolongs IgG and albumin half-life.
FcRn binds IgG or albumin in acidic endosomes and transports them to the cell surface, where neutral pH (7.4) triggers release into circulation. This pH-dependent recycling extends half-life of IgG and albumin from days to weeks, maintaining protective serum levels. The schematic, inspired by reference [14], was redrawn using BioRender.com.
Fig 3.
FcRn as a multifunctional viral entry receptor.
(A) Enterovirus B (EV-B) members (e.g., Coxsackievirus B, Echovirus) attach to cells via CD55 or integrins, while FcRn acts as their exclusive uncoating receptor to enable RNA release. (B) For PRRSV entry into porcine alveolar macrophages, the virus first binds to potential attachment receptors, including heparan sulfate, vimentin, sialoadhesin, MYH9, DC-SIGN, or CD151. The virus is then internalized, and FcRn and CD163 mediate endosomal uncoating. Acidic endosomal conditions allow FcRn to destabilize the virion and facilitate the release of viral genomic RNA into the host cytoplasm. The figure was created with BioRender.com.
Fig 4.
FcRn-mediated viral transcytosis.
Cross-reactive or non-neutralizing antibodies recognizing viruses such as HIV-1, CMV, or ZIKV form virion-antibody complexes that hijack FcRn. This FcRn-dependent pathway mediates transcellular infection across epithelial cells or syncytiotrophoblasts. The figure was created with BioRender.com.