[PROBLEMS] To provide a monoclonal antibody simultaneously detectable the expression of all three kinds of HLA-A, HLA-B and HLA-C heavy chain proteins composing human class I leukocyte antigens (HLA class I) in denatured human tissue samples fixed by formalin and the like.

[MEANS FOR SOLVING THE PROBLEMS] It was discovered that injection of denatured recombinant HILA-A*2402 heavy chain proteins to mouse for immunization led to establish HLA class I-specific antibody binding all of denatured HLA-A, B and C. The present invention is a monoclonal antibody specifically binding HLA-A, HLA-B and HLA-C heavy chains composing denatured human class I antigens, wherein said monoclonal antibody is produced by hybridomas (FERM AP-20454) and bound specifically HLA-A, HLA-B and HLA-C heavy chains composing denatured human class I antigens. Furthermore, the present invention is a test reagent for examining denatured human class I leukocyte antigens containing the monoclonal antibody as a major component.