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Abstract

α2-Macroglobulin (α2M) in the rat is a strong-reacting acute-phase protein with potent protease-inhibiting and cytokine-binding properties. Production of α2M 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 α2M. α2M protein and messenger RNA (mRNA) in the unaffected liver tissue, as well as serum values of α2M, were comparable in control rats and egg-injected rats, at 1, 3, and 8 weeks after injection of the eggs. α2M was homogeneously distributed across the liver lobule. In contrast, at the sites of the granulomas, a strong increase in α2M was observed. α2M mRNA was expressed by granuloma cells, but not by the surrounding liver parenchymal cells. Within the granulomas, α2M 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 α2M-positive cells in the granulomas appeared to be desmin-positive, suggesting a myofibroblast origin. In addition, parenchymal cells directly surrounding the granulomas contained α2M 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 α2M mRNA, suggesting uptake of α2M-protein by these parenchymal cells and previous activation of α2M by proteases within the granuloma. The significance of the present study is that α2M is produced locally at sites of inflammation and liver fibrosis, without measurable increase of serum levels of α2M. Unexpectedly, α2M present at the sites of the granulomas is not produced by the liver parenchymal cells, but rather by granuloma cells.