Localization of alpha2-macroglobulin protein and messenger RNA in rat liver fibrosis: Evidence for the synthesis of alpha2-macroglobulin within Schistosoma mansoni egg granulomas

Abstract

alpha2-Macroglobulin (alpha2M) in the rat is a strong-reacting acute-phase protein with potent protease-inhibiting and cytokine-binding properties. Production of alpha2M is ascribed mainly to liver parenchymal cells. In the present study, we investigated, by means of immunohistochemistry and in situ hybridization, whether fibrosis in the rat liver induced by Schistosoma mansoni eggs leads to local production of alpha2M. alpha2M protein and messenger RNA (mRNA) in the unaffected liver tissue, as well as serum values of alpha2M, were comparable in control rats and egg-injected rats, at 1, 3, and 8 weeks after injection of the eggs. alpha2M was homogeneously distributed across the liver lobule. In contrast, at the sites of the granulomas, a strong increase in alpha2M was observed. alpha2M mRNA was expressed by granuloma cells, but not by the surrounding liver parenchymal cells. Within the granulomas, alpha2M protein was present in numerous spindle-shaped cells and was diffusely distributed in the extra-cellular matrix. Using double-staining techniques, a subpopulation of the alpha2M-positive cells in the granulomas appeared to be desmin-positive, suggesting a myofibroblast origin. In addition, parenchymal cells directly surrounding the granulomas contained alpha2M protein in approximately 50% of the granulomas 1 week after injection of the eggs. In situ hybridization on consecutive sections revealed that these parenchymal cells showed only background activity of alpha2M mRNA, suggesting uptake of alpha2M-protein by these parenchymal cells and previous activation of alpha2M by proteases within the granuloma. The significance of the present study is that alpha2M is produced locally at sites of inflammation and liver fibrosis, without measurable increase of serum levels of alpha2M. Unexpectedly, alpha2M present at the sites of the granulomas is not produced by the liver parenchymal cells, but rather by granuloma cells. (Hepatology 1996 May;23(5):1260-7)