Human inter-α-inhibitor family in inflammation: simultaneous synthesis of positive and negative acute-phase proteins

Abstract

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 more unique heavy (H) chains designated H1, H2 and H3. The three H chains and the bikunin chain are encoded by four distinct mRNAs. These molecules and chains, as well as the corresponding mRNAs, were quantified in sera and liver biopsies from a series of patients with or without mild or severe acute infection. The decrease or increase observed for a given molecule or chain in the serum was in agreement with a similar change in the corresponding liver mRNA. In acute inflammation the H2 and bikunin chains are down-regulated and the relevant molecules (I alpha I, I alpha LI) behave as negative acute-phase proteins, whereas the H3 chain is up-regulated and the corresponding P alpha I molecule is a positive acute-phase protein. Also, P alpha I displays a higher-than-usual M(r); this is probably due to ligand binding. The H1 gene does not seem to be affected by the inflammatory condition. The quantitative changes in RNA levels seen in vivo were confirmed in vitro in the human hepatoma Hep3B cell line prior to or after induction with the acute-phase mediators interleukin-1 and/or -6. These results provide the first example in humans of positive and negative acute-phase proteins that are encoded by evolutionary related genes.