SUMMARYa1-Proteinase inhibitor (a1-PI) is the main serine proteinase inhibitor in human plasma. Apart from its synthesis in the liver, this anti-inflammatory protein is also synthesized by and excreted from human intestinal epithelial cells. Antiinflammatory actions of a1-PI are thought to be of relevance in the pathogenesis of inflammatory bowel disease. To investigate the role of macrophage-derived cytokines on a1-PI secretion from intestinal epithelial cells, we cultured Caco-2 cells until differentiation (14 days in culture) on permeable filter supports. Monolayers of differentiated Caco-2 cells were then co-cultured with human peritoneal macrophages, grown on plastic in the basolateral chamber. Under these conditions, a1-PI secretion from Caco-2 cells was enhanced by 45%, probably by a direct action of macrophage-derived cytokines on Caco-2 cells. To extend this observation further, we treated differentiated Caco-2 cells with macrophage-derived proinflammatory cytokines (IL-1b, IL-8, TNF-a), as well as with lymphocyte-derived cytokines IL-2, IL-6 and IFN-g. As early as after 24 h treatment, IL-2 and IL-8 induced a significant and dose-dependent increase of a-1-PI secretion into cell culture medium; this effect was completely reversed after immunoneutralization by the antibodies against IL-2 and IL-8 a1-PI secretion was only slightly decreased after treatment with IFN-g, while IL-1b, IL-6 and TNFa had no effect. a1-PI secretion correlated well with the expression of this protein in differentiated Caco-2 cells after cytokine treatment, as confirmed by Western blot. Our data imply that, in vitro, a1-PI secretion in enterocyte-like Caco-2 cells is up-regulated by IL-2 and IL-8. Our results suggest that both lymphocyte-and macrophage-derived cytokines regulate secretion of the anti-inflammatory protein a1-PI in intestinal epithelial cells.

Our data show that butyrate inhibits alpha1-PI release from Caco-2 colonocytes treated with IL-1beta. It is therefore likely that anti-inflammatory actions of butyrate occur via a mechanism that does not involve direct regulation of cytokine-induced anti-inflammatory protein expression in intestinal epithelial cells.

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