The present inventors have successfully prepared an antibody Fc region dimer that has binding activity against each of an antigen and Fc³R, but does not bind to the antigen and the Fc³R at the same time, and a polypeptide comprising the Fc region dimer. The present invention enables the preparation of a multispecific binding polypeptide capable of avoiding an adverse reaction that may be caused by its binding to an antigen and Fc³R at the same time. Thus, the present invention provides a polypeptide suitable as a drug.
