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Qu M., You J., Li G., Ouyang K., Huang J.
College of Animal Science and Technology/Jiangxi Province Key Laboratory of Animal Nutrition, Jiangxi, Agricultural University, China

Defensins serve as crucial components of the innate immune system and play an essential role in the host defense against infection. In addition to their direct broad-spectrum antimicrobial activities against Gram-positive and Gram-negative bacteria, fungi and some enveloped viruses, defensins can function as potent immune regulators and act as a bridge between innate and adaptive immunity. AMPs can act as signal molecules between cells to play multiple functions in immune defense against infection.The avian beta-defensin 9 (AvBD9), an important antimicrobial peptide expressed in chicken tissues, especially in the digestive tract and immune tissues, plays a crucial role in maintaining the homeostasis of gastrointestinal microflora and shows multiple functions in immune defense against infection. Our previous study has demonstrated that probiotic Lactobacillus rhamnosus (L. rhamnosus) MLGA and the whole cell wall peptidoglycan (WPG) from L. rhamnosus MLGA induced AvBD9 expression in primary cultured chicken small intestinal epithelial cells.

In this study, the effects of WPG on AvBD9 mRNA expression in immune cells from different tissues and intestine of chicken were investigated, and the different effects of peptidoglycan from pathogenic bacteria and probiotics on AvBD9 gene expression were compared. The proinflammatory cytokines expression in immune cells in response to WPG stimulation were determined to define whether or not the AvBD9 expression induced by WPG was inflammatory cytokine-dependent. Moreover, the antibacterial effect of cell lysates from coculture of immune cells with Lactobacillus rhamnosus-derived WPG was determined.

WPG from L. rhamnosus MLGA promoted AvBD9 mRNA expression with different potential in chicken peripheral blood mononuclear cells (PBMCs), splenocytes, thymocytes, liver cells and chick embryo jejunum, ileum, cecum explants in a dose-dependent manner. Differences in the magnitude of up-regulation of AvBD9 expression triggered by WPG between different cells or different intestinal segments were observed. In contrast to the effect of L. rhamnosus-derived WPG, Staphylococcus aureus-derived peptidoglycan down-regulated AvBD9 mRNA expression in chicken PBMCs and splenocytes. Pro-inflammatory cytokines IL-1β, IL-8 and IL-12p40 mRNA expressions in chick PBMCs and splenocytes were not significantly affected by L. rhamnosus MLGA WPG, whereas these cytokine expressions in chick PBMCs and splenocytes were significantly suppressed by hydrolysate of Lactobacillus rhamnosus MLGA WPG. The L. rhamnosus-derived WPG and its hydrolysate by lysozyme promoted AvBD9 expression without being accompanied by inflammatory response. The growth of Salmonella enteritidis (S. enteritidi) was significantly inhibited by cell lysates from coculture of PBMCs or splenocytes treated with L. rhamnosus-derived WPG. The antimicrobial effect of cell lysates was increased with the increase of WPG concentrations. L. rhamnosus-derived WPG itself showed no inhibitory effect on the growth of S. enteritidi.

Collectively, the results in the present study indicated that L. rhamnosus MLGA derived-peptidoglycan and its hydrolysate can exert beneficial effects to the host and enhance the innate defense response against infection through the upregulation of β-defensin such as AvBD9 expression in tissues especially in immune cells of chicken.

Keywords: Innate immunity, Proinflammatory cytokines, Probiotic, Avian Beta-Defensin 9, Peptidoglycan, Chicken

Qu M., et al. (2016). Peptidoglycan from Lactobacillus Rhamnosus promotes avian beta-defensin 9 gene expression in immune cells and intestine of chicken. Conference Proceedings of IPC2016. Paper presented at the International Scientific Conference on Probiotics and Prebiotics, Budapest (p. 59.). IPC2016

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