Method for improving binding affinity of igg antibody to fcrn and prolonging serum half-life period thereof

Provided is a method for improving the binding affinity of an IgG antibody to FcRn and prolonging a serum half-life period thereof. An objective of the method is to allow amino acids at No. 254, 308 and 434 sites in FcRn binding site regions in a heavy chain constant region of the IgG antibody to have mutations.