PROBLEM TO BE SOLVED: To provide antibody Fc regions in which an amino acid sequence is modified from a naturally-occurring antibody Fc region, to provide antibodies comprising the Fc regions, to provide pharmaceutical compositions comprising the antibodies, and production methods thereof.SOLUTION: The present invention provides a polypeptide in which stability is improved as compared with its parent polypeptide, by modifying at least one amino acid of a loop site of the Fc region of an antibody. Also provided are a polypeptide in which the binding activity to FcγR is maintained or enhanced while thermal stability is improved as compared with its parent polypeptide, by combining a plurality of amino acid modifications of a loop site； and a polypeptide in which the binding activity to FcγR is reduced while the thermal stability is improved； and additionally a polypeptide in which the binding activity to FcγR is not only adjusted while the thermal stability is improved, but the content of an assembly is also reduced.SELECTED DRAWING: Figure 1【課題】天然由来の抗体Fc領域からアミノ酸配列が改変された抗体Fc領域、該Fc領域を含む抗体、該抗体を含む医薬組成物、ならびに、それらの製造方法の提供。【解決手段】抗体のFc領域のループ部位における少なくとも一つのアミノ酸を改変する事により、親ポリペプチドと比較して安定性が向上したポリペプチドを提供する。さらに、ループ部位のアミノ酸の改変を複数組み合わせ、親ポリペプチドと比較して、熱安定性を向上させつつFcγRへの結合活性が維持又は増強したポリペプチド、及び熱安定性を向上させつつFcγRへの結合活性が減少したポリペプチド、さらには熱安定性を向上させつつFcγRへの結合活性を調整するだけでなく、会合体含有量が減少したポリペプチドを提供する。【選択図】図１
