ALPHA(1)-MICROGLOBULIN IS FOUND BOTH IN BLOOD AND IN MOST TISSUES

In this study we demonstrate that, in addition to blood, alpha(1)-micr oglobulin (alpha(1)m) is present in most tissues, including liver, hea rt, eye, kidney, lung, pancreas, and skeletal muscle. Western blotting of perfused and homogenized rat tissue supernatants revealed aim in i ts free, monomeric form and in high molecular weight forms, correspond ing to the complexes fibronectin-alpha(1)m and alpha(1)-inhibitor-3-al pha(1)m, which have previously been identified in plasma. The liver al so contained a series of alpha(1)m isoforms with apparent molecular ma sses between 40 and 50 kD. These bands did not react with anti-inter-a lpha-inhibitor antibodies, indicating that they do not represent the a lpha(1)m-bikunin precursor protein. Similarly, the heart contained a 4 5-kD alpha(1)m band and the kidney a 50-kD alpha(1)m band. None of the se alpha(1)m isoforms was present in plasma. Immunohistochemical analy sis of human tissue demonstrated granular intracellular labeling of al pha(1)m in hepatocytes and in the proximal epithelial cells of the kid ney. In addition, alpha(1)m immunoreactivity was detected in the inter stitial connective tissue of heart and lung and in the adventitia of b lood vessels as well as on cell surfaces of cardiocytes. alpha(1)m mRN A was found in the liver and pancreas by polymerase chain reaction, su ggesting that the protein found in other tissues is transported via th e bloodstream from the production sites in liver and pancreas. The res ults of this study indicate that in addition to its role in plasma, ai m may have Important functions in the interstitium of several tissues.