Quantification of free alpha 2-macroglobulin and alpha 2-macroglobulin-protease complexes by a novel ELISA system based on streptococcal alpha 2-macroglobulin receptors.

An ELISA test system has been developed for the quantification of the two distinct forms of the proteinase inhibitor alpha 2-macroglobulin (alpha 2M): (i) free alpha 2M (functionally active), which is the electrophoretically slow form (alpha 2 MS), and (ii) the alpha 2 M-proteinase complex (functionally inactive), which is the electrophoretically fast form of alpha 2 M (alpha 2 MF). Discrimination between the two types of alpha 2 M was achieved using extracts of the two independent streptococcal strains, M1 and Sc1, which express receptors for alpha 2 MS and alpha 2 MF, respectively, in combination with a monoclonal antibody specific for alpha 2 M. The assay system described is easy and reliable and permits quantitation of alpha 2 MS and alpha 2 MF in complex biological samples such as plasma and cutaneous suction blister fluid.