The purpose of the present invention is to provide: a polypeptide containing an Fc region of which the activity of binding to both of genetic polymorphism types H and R of FcγRIIa is maintained or reduced compared with that of a parent polypeptide and of which the activity of binding to FcγRIIb is enhanced compared with that of the parent polypeptide a pharmaceutical composition containing the polypeptide a therapeutic or prophylactic agent for immune/inflammatory diseases, which comprises the pharmaceutical composition processes for producing those products and a method for maintaining or reducing the activity of binding to both of the above-mentioned genetic polymorphism types of FcγRIIa or enhancing the activity of binding to FcγRIIb. Specifically, it is found that a polypeptide which contains an antibody Fc region that contains a mutation produced by substituting Pro located at 238th position as numbered in accordance with the EU numbering method by Asp and a mutation produced by substituting Leu located at 328th position as numbered in accordance with the EU numbering method by Glu is enhanced with respect to the activity of binding to FcγRIIb and is maintained or reduced with respect to the activity of binding to both of genetic polymorphism types H and R of FcγRIIa. It is also found that a polypeptide which contains an antibody Fc region that contains a mutation produced by substituting Pro located at 238th position as numbered in accordance with the EU numbering method by Asp and another type of mutation is enhanced with respect to the activity of binding to FcγRIIb and is maintained or reduced with respect to the activity of binding to both of genetic polymorphism types H and R of FcγRIIa.La présente invention concerne : un polypeptide contenant une région Fc dont lactivité de liaison aux deux polymorphismes génétiques de type H et R de FcγRIIa est conservée ou réduite par rapport à celle dun polypeptide parent et dont lactivité de liaison à FcγRIIb est ren
