I-alpha-I plasma protease inhibitors are assembled from one or two heavy chains (H1, H2 or H3) and one light chain, bikunin. Inter-alpha-inhibitor (I-alpha-I) is composed of H1, H2 and bikunin, inter-alpha-like inhibitor (I-alpha-LI) of H2 and bikunin, and pre-alpha-inhibitor (P-alpha-I) of H3 and bikunin. Alpha-1-microglobulin occurs as a monomer and also in complexes with IgA and albumin. Alpha-1-microglobulin interacts with FN1. Trypstatin is a monomer and also occurs as a complex with tryptase in mast cells (By similarity). Alpha-1-microglobulin and bikunin interact (via SH3 domain) with HEV ORF3 protein.