Farm animals often suffer from diseases of the gastro-intestinal tract. Modulation of natural defence mechanisms by dietary additives may be one way to improve intestinal health and food safety. In mammals, antimicrobial peptides (AMPs) play an important role in the host defence of skin and mucosal surfaces. We sought for novel members of known antimicrobial peptide families using in silico analysis and discovered 7 unknown chicken beta-defensins (AvBDs) and one chicken cathelicidin (CMAP27). High, breed-independent AvBD9 mRNA expression was found in crop and esophagus tissue. Promoter analysis of the AvBD9 gene as well as AvBD9 mRNA expression variability observed in the crop tissue of young animals, suggested an inducible nature of the AvBD9 gene. CMAP27 mRNA was highly and predominantly expressed in myeloid and lymphoid tissues. Abundant CMAP27 protein was found in heterophilic granulocytes, but not in other peripheral blood cells. Considerable infiltration of CMAP27 containing heterophils was observed in the jejunum of Salmonella-challenged 4 day-old chicken broilers at 8 and 48 hours post infection as compared to non-infected animals; however, CMAP27 expression was not induced in intestinal epithelial cells. Synthetic AvBD9 and CMAP27 peptides showed potent broad spectrum antimicrobial activity against bacteria and fungi. Their potent antimicrobial properties and possible upregulation and mobilisation at mucosal interfaces render these peptides prime candidates to be investigated in studies addressing AMP modulation by dietary modulation
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