The present invention has the first object to provide a monoclonal antibody specific to interferon α subtype α8 (IFNα8) and its mutant proteins, the second object to provide a hybridoma capable of producing the monoclonal antibody, the third object to provide a method for detecting the IFNα8 and its mutant proteins by the monoclonal antibody, the fourth object to provide a method for purifying the IFNα8 and its mutant proteins by the monoclonal antibody, and the fifth object to provide a therapeutic agent for treating diseases whose onsets or exacerbation are related with IFNα8. The present invention solves the above objects by providing a monoclonal antibody specific to IFNα8 and its mutant proteins, a hybridoma capable of producing the monoclonal antibody, a method for detecting the IFNα8 and its mutant proteins by immunoreaction using the monoclonal antibody, a method for purifying the IFNα8 and its mutant proteins using the monoclonal antibody, and a therapeutic agent for treating diseases whose onsets or exacerbation are related with IFNα8, which contains the monoclonal antibody as an effective ingredient.
