Novel monoclonal antibodies specific for human cardiac myosin light-chain 1: useful tools for analysis of normal and pathological hearts.

To investigate the developmental, physiological and pathophysiological roles of human cardiac myosin light-chain 1 (LC1s), we developed two novel monoclonal antibodies (KA1 and KB1) against human cardiac LC1s and examined LC1s in normal and pathological hearts immunohistochemically. KA1 and KB1 were specific only for atrial LC1 (ALC1) and for both ALC1 and ventricular LC1 (VLC1), respectively, in human hearts. Among human tissues tested, including skeletal muscle, vascular smooth muscle, and liver, KA1 did not crossreact with proteins in any other tissues than atria, whereas KB1 crossreacted with the slow-type LC1 of skeletal muscle. Among adult mammalian hearts of several other species including pig, dog, hamster, and rat, KA1 and KB1 crossreacted only with ALC1 and with both ALC1 and VLC1, respectively. ALC1 was strongly and uniformly observed in human fetal atria and ventricles and in normal adult human atria, but sporadically in normal adult human ventricles. In the overloaded ventricle (dilated cardiomyopathy), ALC1 was highly augmented but not uniform. These results suggest that the fetal VLC1 is immunohistochemically identical to the adult type of ALC1 and that ALC1 is expressed homogeneously in human fetal ventricles and sporadically in normal adult ventricles, and is re-expressed heterogeneously and in an increased amount in the overloaded ventricle.