[Medico-legal studies on detection of organ-specific antigens]

When the organs have been injured, specific antigens pertaining to the organs could be expected to be released into the circulation and/or adhere to the weapons which has inflicted the damage to the organs. We could thus be able to identify the injured organs, if we could detect the antigens specific to the organs in blood of the victim and/or in bloodstains left on the weapons. 1. Liver-specific antigen (LSA). The liver-specific antigen (LSA) was purified from the human liver and was showed to have a molecular mass of 52 kDa and pI of 5.8-5.9. Anti-human LSA antibody only reacted with the liver extract using immuno-dot-blotting technique, and depending on the immunohistochemistry, this antigen was located within the cytoplasm of hepatocytes. The human LSA was proved to be a novel protein, isolated from the human liver, by the NH2-terminal amino acid sequence analysis. Anti-human LSA Fab'-peroxidase conjugate was prepared and a highly sensitive and specific sandwich enzyme immunoassay for human LSA was developed. The detection limit of this assay was 0.52 pg/tube. The LSA levels in the serum and blood of cadavers with liver injuries were markedly increased. These findings suggest that the human LSA will become a useful marker for detecting liver injury. 2. Sucrase-Isomaltase (SI). A sandwich enzyme immunoassay for SI, a dimeric digestive enzyme, was developed using pig as a model animal. SDS-solubilized proteins from the small intestine contained at least 50-fold larger SI than those from the other organs. Significant amount of SI could be detected in small intestinal contents and in stains left on the knife which had been stabbed into the small intestine. These results suggested that SI was a possible forensic marker for small intestinal injuries, although human SI remained to be examined. 3. Cardiac Troponin I (cTnI). The purpose of our study is to identify injuries to the heart from a small amount of blood quickly and accurately by using a sensitive enzyme immunoassay for cardiac troponin I (cTnI), a heart specific protein. Accordingly we purified cTnI from bovine cardiac muscle and prepared the antibody against cTnI in order to develop this assay. We furthermore investigated the usefulness of this antibody by immuno-dot-blotting. As the result, it was confirmed that this antibody reacted against only heart. 4. Dystrophin. The purpose of this work is to develop a method to determine skeletal muscle injuries using muscle-specific substances. Dystrophin was purified from SDS-solubilized bovine skeletal muscle.