CXADR is a Human IgG Fc Receptor

CXADR is a membrane protein present in epithelial tight junctions and other tissues with a variety of known functions, in addition to its role as entry receptor for coxsackie B virus and adenovirus 2 and 5. We identified a previously unknown function of CXADR as a binding partner for human IgG but not IgA, IgE, IgM, or ScFv in a non paratope specific manner. Binding was specific to human and rabbit IgG, and not observed for mouse, rat, donkey, or goat IgG. Binding of Ig to CXADR is inhibited by FcBlock (BD), and is competitive with anti-Fc binding secondary antibodies, but not anti-Fab secondary antibodies, indicating that CXADR binds the Fc portion of IgG. CXADR, being a member of the immune superfamily of proteins, has similar structural homology to other Ig binding proteins, including Fc receptors. We conclude that CXADR has a previously unknown function as a human Fc receptor, serving as a direct link between the humoral adaptive immune system and many cell types in the human body previously unknown to express FcR.