Electrophoretic pattern of the inter-alpha-inhibitor family proteins in human serum, characterized by chain-specific antibodies.

The inter-alpha-inhibitor (I alpha I) family encompasses four plasma proteins, namely free bikunin as well as I alpha I, pre-alpha-inhibitor (P alpha I) and inter-alpha-like inhibitor (I alpha LI). Each of the last three proteins is a distinct assembly of one bikunin chain with one or two out of three distinct, heavy (H) chains designated H1, H2 and H3. I alpha I is made of [H1 + H2 + bikunin], P alpha I is made of [H3 + bikunin] and I alpha LI is made of [H2 + bikunin]. We characterized various I alpha I family-related antisera/antibodies, including a reagent recognizing bikunin, another directed against the four H1, H2, H3 and bikunin chains, and a third one directed against both H1 and H2 chains. By a simplified absorption procedure of the latter two antisera onto solid-phase immunoadsorbents made with i) purified I alpha I, or ii) a recombinant H1 polypeptide, we also obtained specific anti-H3 or anti-H2 antibodies, respectively. This series of new antibodies was used to identify each component within the pattern of bands corresponding to I alpha I family in human serum, as separated by SDS-PAGE and western blotting.