Citrus pectins impact the function of chicken macrophages

The restrictions on excessive use of antimicrobials in the poultry industry have led to the search for alternative strategies including nutritional interventions to enhance gut health with the ultimate aim to prevent gut infections. Pectins as prebiotics have shown beneficial effects on gut health in humans and mice by improving the gut barrier function, altering the gut microbiota, and by modulating the gut immune response. However, little is known about immunomodulatory properties of pectins in chickens. The present in vitro study assessed the effect of three pectins (SPE6, SPE7, SPE8) differing in methyl esterification, on responsiveness of the chicken macrophage cell line HD11 cells and primary monocyte derived macrophage from the blood, through interaction with chicken TLRs. All three pectins increased gene expression of iNOS and IL10 in chicken macrophages. Differences in immunomodulatory activity between the three pectins were observed in other assays. The low methoxyl pectin (SPE8) interacted with TLR4 leading to the production of NO, but also to increased phagocytosis of E. coli, while high methoxyl pectins SPE6 and SPE7 did not activate TLR4. All three pectins were able to attenuate PAM3CSK4 induced activation of chicken macrophages as measured by decreased NO production and phagocytosis. Additional studies using ITC and flow cytometry suggest that the inhibiting properties of pectins (SPE6, SPE7) on macrophages are due to pectins occupying TLR2 and blocking PAM3CSK4 to activate chicken macrophages, whereas SPE8 actually binds to the TLR2 ligand and that way attenuates the PAM3CSK4 induced activation. Based on these immunomodulatory properties observed in this study, these pectins may in the future be suitable as feed additive for the treatment and prevention of inflammatory disorders in poultry.