The present invention relates to use of an antagonist of BIR1 (B cell immunoglobulin receptor 1) related to the present invention, a method for screening the antagonist, in addition to subtype polypeptides of BIR1, the polynucleotide encoding them and antibodies for the polypeptides. BIR1 functions as an immunosuppressive receptor, and the antagonist of BIRI has immunopotentive activity, which is able to use for preventing and/or treating a cancer, an immunodeficiency disease or an infectious disease.
