Purification and properties of human alpha-2-macroglobulin from serum and lymphoid culture supernatants

A purification method has been developed for alpha-2-macroglobulin (a2M) which allows efficient, fast production of purified protein from samples of serum or culture supernatant. The a2M obtained by this method is of extremely high purity as shown by rigorous analytical methods not previously met by other laboratories. The purified molecule has been analyzed electrophoretically and was shown to consist of two loosely bound subunits which could be dissociated by mild conditions such as pH change or exposure to 3 M urea. This subunit could be further dissociated by reductive alkylation with mercaptoethanol to yield two types of subunits having molecular weights of approximately 50,000 to 31,000. The a2M purified from 1788 lymphocyte culture supernatant was shown to be a carrier of various lymphokine activities, including lymphotoxin and macrophage activation factor. It also had more protease associated with it than a2M isolated from control culture medium. Alpha-2-macroglobulin was also shown to be synthesized by the 1788 lymphocytes, confirming our data obtained by autoradiographic and kinetic radioimmunoassay. The results of these studies establish the techniques and basic structural and functional information necessary for a more detailed study of the physical and biological properties of a2M in relation to its role as a lymphokine carrier and, thereby, of its immunotherapeutic potential.