IgG molecules of the IgG1, IgG2, and IgG4 subclasses exhibit exceptionally long half-lives due to FcRn-mediated recycling. Half-lives of up to 4 weeks have been described for therapeutic antibodies. The binding site for FcRn resides in the Fc region is formed by the CH2 and CH3 domains. Thus, fusion to an Fcγ region endows a therapeutic protein with the half-life extension properties (increased size, FcRn recycling) of immunoglobulins. Learn more: