FcRn

FcRn, or neonatal Fc receptor, is a key regulator of IgG antibody and albumin homeostasis, widely expressed in endothelial and epithelial cells. It functions by binding to the Fc region of IgG and to albumin at acidic pH within endosomes, protecting them from lysosomal degradation and recycling them back to the cell surface at physiological pH. This recycling mechanism significantly extends the half-life of circulating IgG and albumin, maintaining stable antibody and protein levels essential for immune protection and nutrient transport. Beyond its role in molecular recycling, FcRn also contributes to immune surveillance by transporting IgG and immune complexes across epithelial barriers, facilitating antigen presentation and immune regulation. Altered FcRn function, whether through genetic variation, overexpression, or therapeutic modulation, can profoundly impact antibody pharmacokinetics and immune homeostasis. Dysregulation has been associated with autoimmune diseases such as myasthenia gravis and systemic lupus erythematosus, where abnormal IgG persistence amplifies pathogenic immune responses. In therapeutic contexts, FcRn has become an important target for monoclonal antibodies and engineered biologics designed to either extend antibody half-life or promote rapid clearance of pathogenic IgG. These strategies are transforming the treatment landscape for antibody-mediated disorders, making FcRn a central focus of immunology and drug development research.