Abstract: The distribution of relevant antigen in normal tissues and in pathological lesions were studied by HIT6_1 monoclonal antibodies with APAAP immunohistochemical method.The tissues used for assay including heart,smooth and skeletal muscle,liver,lung,kidney,brain, thyroid gland,thymus,GI tract of fetus,and liver,kindey,tonsil,lymph node and bone marrow of normal adult and spleen of patients with ITP and hemolytic anemia,tonsil of patients with aplastic anemia,cancer of esophagus and lung,and tissues of 12 cases of SLE in active stage.Over 95% lymphoid cells in thymus torttex,interdigitating cells in interfollicular area of tonsil,paracortex of lymph node,and red pulp of spleen,and Langerhans cells in the epidermis and supperfieial layer of dermis could express HIT6_1 antigen.Our result indicates that HIT6_1 is a CD1(OKT6)-like monoclonal antibody.It was also proved that the number of Langerhans cells in the skin lesions of SLE significantly reduced than that of normal,their morpholog were also abnormal.