Pig MAP/ITIH4 and haptoglobin are interleukin‐6‐dependent acute‐phase plasma proteins in porcine primary cultured hepatocytes

Abstract

The acute-phase expression of pig MAP (major acute-phase protein)/ITIH4 (inter-alpha-trypsin inhibitor heavy chain 4) and haptoglobin were analysed in primary cultures of isolated pig hepatocytes in response to recombinant human (rh) cytokines: tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1), interleukin-6 (IL-6), as well as to bacterial lipopolysaccharide (LPS). Analysis of pig MAP/ITIH4 and haptoglobin mRNAs was carried out by RT-PCR amplification. Secreted proteins from the cytokine-treated hepatocytes were quantified by immunochemical techniques. Time-course and dose-response experiments show that pig MAP/ITIH4 and haptoglobin belong to the type II acute-phase proteins, as they are specifically induced by rhIL-6 and not by rhTNF-alpha or rhIL-1. Stimulation of cultured pig hepatocytes with rhIL-6 for 48 h at doses of 1000 U.mL-1 showed a fourfold to fivefold increase in pig MAP/ITIH4 concentration in the medium, while the concentration of haptoglobin only increased twofold. A similar increase in the concentration of pig MAP/ITIH4 was also observed in media of LPS-treated hepatocytes with the simultaneous generation of IL-6 by the Kupffer cells present in the cultures. Albumin secretion decreased after stimulation with doses of 100 or 1000 U.mL-1 rhTNF-alpha, rhIL-1 or rhIL-6. Therefore, it can be concluded that pig MAP/ITIH4 behaves as a major acute-phase protein produced by porcine hepatocytes under the effect of inflammatory cytokines.