Table I.

Functions of FcRn across a variety of tissues and associated therapeutic implications

Functions of FcRn	Tissue/cell type							Therapeutic implications
	Intestines	Mammary gland	Placenta	Lung	Hematopoietic cells	Kidney	Liver
Bidirectional transcytosis of IgG	Postnatal maternal to fetal IgG transfer [28, 49–51].	Transport of IgG into colostrum and milk [55].	Prenatal maternal to fetal IgG transfer [49, 67–69].	Transfer of IgG into pulmonary secretions [76].		Reabsorption of IgG from the glomerular basement membrane [88, 89].		Pulmonary or oral delivery of Fc fusion proteins to systemic circulation [79, 81].
	Import of luminal antigens as immune complexes [51].	Recycling of IgG back into maternal circulation [59].						Inhibition of trans-placental pathogenic antibody transport [73].
								Treatment of illness linked to deposition of immune complexes [88, 89].
Catabolism protection of IgG					Protection of monomeric IgG from degradation [40].		Protection of IgG from catabolism and biliary loss [94] (Kuo, unpublished)	Treatment of autoimmune disorders caused by pathogenic IgG [107, 110].
					Promotion of multimeric IgG degradation [40].			Engineered antibody-based therapy with prolonged half-life [107].
Catabolism protection of albumin						Reabsorption of albumin by proximal tubular epithelial cells [90].	Regulation of albumin homeostasis [13].	Prolongation of the half-life of drugs conjugated to albumin [118].
							Prevent biliary loss of albumin (Kuo, unpublished).
Antigen presentation	Delivery of immune complexes to resident antigen presenting cells [51].				Promotion of MHC class II restricted antigen presentation [40].			Eradication of IgG-opsonized intestinal pathogens [52].
					Clearance of IgG-opsonized bacteria [86].			Priming of immune responses against IgG-complexed antigen [54].