[Clinical application of immunoassays for cardiac myosin light chains]

We developed four types of immunoassays for cardiac myosin light chains (LC), which are two radioimmunoassays (RIA) for canine and human LC, and an immunoradiometric assay (IRMA) and an enzyme-linked immunosorbent assay (ELISA) for human LC. The first two assays make use of polyclonal antibodies and the last two use monoclonal antibodies. By using these immunoassays, we studied the release of cardiac LC into the serum following acute myocardial infarction (AMI). In experimental AMI in dogs, cardiac LC appeared in the serum within 4-12 hours, reached the maximum at 2-5 days and returned to normal at 7-10 days. This long time-course was suggested due to the continuous liberation of LC from the infarcted myocardium on the basis of a quick disappearance rate of LC from the circulation. The peak LC values were found to correlate well with the histological infarct size. Similar results were also obtained regarding the time-course of circulating LC in clinical patients with AMI. Thus LC measurement seems useful for diagnosis of AMI as well as for estimating the extent of myocardial damage. We also developed an IRMA and an ELISA for human LC by using anti-human LC monoclonal antibodies for a more rapid LC assay and for a consistent supply of antibodies. These assays showed sufficiently high sensitivities to measure 1-100 ng/ml of serum LC. Especially, serum LC can be assayed within 2.5 hours by our ELISA. Such progress in immunoassays for cardiac LC has made the measurement of LC an important laboratory test for the diagnosis of AMI.