PROBLEM TO BE SOLVED: To provide: an antigen binding molecule with enhanced uptake of antigen into cells； an antigen binding molecule with an increased number of bonds to an antigen； an antigen binding molecule which can promote the decrease of antigen concentration in blood plasma when administered； and an antigen binding molecule with improved retention in blood plasma.SOLUTION: An antigen binding molecule comprises an antigen binding domain and a human FcRn binding domain, in which the antigen binding activity under two different calcium concentration conditions is different, the antigen binding activity of the antigen binding molecule under low calcium concentration conditions being lower than antigen binding activity under high calcium concentration conditions, and which has binding activity to human FcRn under neutral pH conditions.SELECTED DRAWING: None【課題】抗原の細胞内への取込みが促進された抗原結合分子、抗原への結合回数が増加した抗原結合分子、投与により血漿中の抗原濃度の減少を促進させることができる抗原結合分子、血漿中滞留性が改善された抗原結合分子を提供する。【解決手段】抗原結合ドメインとヒトFcRn結合ドメインを含む抗原結合分子であって、２つの異なるカルシウム濃度条件下における抗原結合活性が異なり、抗原結合分子の低カルシウム濃度条件下における抗原結合活性が、高カルシウム濃度条件下における抗原結合活性より低く、中性pH条件下においてヒトFcRnに対する結合活性を有する抗原結合分子。【選択図】なし
