Abstract: It is an object of the present invention to a method whereby a humoral immune response is induced more efficiently in producing an antibody against an antigen protein by gene immunization. A fusion gene composed of a gene encoding the full-length of a part of the antigen protein or a gene encoding a chaperonin subunit or a chaperonin subunit linkage linked thereto is administered to express the fusion gene in the animal, thereby inducing a humoral immune response to an antigen protein by administering. An example of the chaperonin includes Escherichia coli GroEL. There is also provided with a composition for immunization, a method for producing an antibody, a method for producing a hybridoma, and a method for producing a monoclonal antibody.

Abstract: A hepatitis C virus antigen polypeptide having a molecular weight of approximately 22 kilodaltons expressed from a hepatitis C virus structural gene region; a production method for a hepatitis C virus antigen polypeptide having a molecular weight of 22 kilodaltons and/or a peptide related thereto, wherein an expression vector having inserted thereinto a cDNA fragment of a hepatitis C virus structural gene region is inserted into a cultured cell line and the transfected cell line thus obtained is cultured; and a detection method for a hepatitis C virus antibody, wherein a hepatitis C virus antigen polypeptide is used as an antigen, and an antibody specific thereto is detected.

Abstract: A hepatitis C virus antigen polypeptide having a molecular weight of approximately 22 kilodaltons expressed from a hepatitis C virus structural gene region; a production method for a hepatitis C virus antigen polypeptide having a molecular weight of 22 kilodaltons and/or a peptide related thereto, wherein an expression vector having inserted thereinto a cDNA fragment of a hepatitis C virus structural gene region is inserted into a cultured cell line and the transfected cell line thus obtained is cultured; and a detection method for a hepatitis C virus antibody, wherein a hepatitis C virus antigen polypeptide is used as an antigen, and an antibody specific thereto is detected.

Abstract: The antigenic peptide represented by the following amino acid sequence (SEQ ID NO: 1) ##STR1## and a method of the detection of anti-HCV antibodies wherein the above peptide is brought into contact with a sample under the conditions that the peptide is bound to anti-HCV antibodies present in the sample to form an immunological complex and the formation of the immunological complex is measured to confirm the existence of the anti HCV antibodies in the sample. The method is highly specific and sensitive to anti-HCV antibodies.