Antimicrobial Peptides Expression for Defense System in Chicken Gastrointestinal and Reproductive Organs

Abstract

Maintenance of animal health is essential to obtain their maximum productivity and safe products. Avian β-defensins (AvBDs) are the member of antimicrobial peptides, and Toll-like receptors (TLRs) are the primary receptors that recognize pathogen-associated molecular patterns (PAMPs) of microbes. The aim of this study was to characterize the innate immune system with the focus on the expression of AvBDs in the gastrointestinal tract and reproductive organs for the strategy to enhance the disease resistance of chickens. The proventriculus and cecum of broiler chicks expressed TLRs and AvBDs. It is suggested that a variety of PAMPs of microbes are recognized by different TLRs, probably leading to regulate the synthesis of innate immune factors including AvBDs. In laying hens, TLRs and AvBDs were expressed in the theca and granulosa layers of ovarian follicles and in the oviduct. In vivo LPS challenge increased the expression of several AvBDs in the theca tissue. In contrast, in the cultured theca tissue, LPS upregulated the expression of IL1β and IL6, but did not affect the AvBDs expression; whereas IL1β upregulated the expression of the AvBD12 gene and protein. It suggests that LPS of Gram-negative bacteria are recognized by TLR4 to induce the IL1β expression, and then IL1β upregulates the AvBD expression in the infected tissues. The expression of AvBDs, IL1β and IL6 in the vagina was upregulated by Salmonella and LPS challenge. Meanwhile, the AvBD1 and 3 expression was upregulated by IL1β, suggesting that the synthesized IL1β may participate to induce AvBDs. The results of this study suggest that innate immune system with TLRs and AvBDs is developed in the chicken gastrointestinal tract and reproductive organs. Improvement of innate immune functions by AvBDs in chickens may be one of the important strategies for enhancing the disease resistance in chickens.