Abstract
The aim of this study was to investigate whether glycyrrhizin, with steroid hormone-like effects, can upregulate expression of secretory component (SC) in human colonic epithelial Caco-2 and to explore its underlying mechanism. Cultures of Caco-2 were exposed to glycyrrhizin. Free SC in culture supernatants, SC protein, and SC mRNA expression were measured by enzyme-linked immunosorbent assay (ELISA), western blot, real-time PCR, respectively. Cultures of Caco-2 were exposed to RU486, a glucocorticoid receptor (GR) antagonist, combined with glycyrrhizin or dexamethasone (DEX), SC protein and SC mRNA expression were examined. Glycyrrhizin dose-dependently upregulated free SC in culture supernatants, SC mRNA and protein expression of SC (p<0.05). RU486 could inhibit DEX effects on SC expression (p<0.05), but did not inhibit glycyrrhizin effects on SC expression (p>0.05). The present study indicates that glycyrrhizin has a glucocorticoid-like upregulated effect on SC production in Caco-2 cells. It is likely that this effect is different from the mechanism of glucocorticoids. Key words: Licorice, glucocorticoid, polymeric Ig receptor, glucocorticoid receptor.
Highlights
The mucosal immune system provides the first line of defense against the entrance of a multitude of ingested and inhaled microorganisms (Tjärnlund et al, 2006)
secretory component (SC) plays a protective role in preventing the proteolytic degradation of polymeric immunoglobulin A (IgA), enhancing the mucosal immunity provided by IgA at these sites; Free SC is important for the enhancement of immune responses
Degranulation of eosinophils caused by binding of secretory immunoglobulin A S-IgA or SC is mediated through the 15.000 MW SC receptor expressed in eosinophils (Motegi et al, 1998; Lamkhioued et al, 1995)
Summary
The mucosal immune system provides the first line of defense against the entrance of a multitude of ingested and inhaled microorganisms (Tjärnlund et al, 2006). Secretory component (SC), a key antibody in mucosal immune defenses, is the extracellular cleaved ectodomain of the polymeric immunoglobulin receptor (pIgR) that is responsible for the transcytosis of newly synthesized immunoglobulin A (IgA) (Crottet et al, 1998). SC plays a protective role in preventing the proteolytic degradation of polymeric IgA, enhancing the mucosal immunity provided by IgA at these sites; Free SC is important for the enhancement of immune responses. Degranulation of eosinophils caused by binding of secretory immunoglobulin A S-IgA or SC is mediated through the 15.000 MW SC receptor expressed in eosinophils (Motegi et al, 1998; Lamkhioued et al, 1995). Increasing evidence indicates that high SC expression is important in limiting the inflammatory response to bacterial and viral products, via the antiinflammatory function of SC (Davids et al, 2006; Giugliano et al, 1995; Dallas et al, 1998)
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