| Defensins are important components of the living body’s innate immunity. In addition to their broad-spectrum direct microbicidal activity, defensins also act as immune effector molecules between cells to play multiple functions in immune defense against infection.However, the mechanisms of action by which defensins protect host against infection and the regulatory mechanism underlying the defensin gene expression by nutrients remain unclear.In this study, the whole cell wall peptidoglycan(WPG) was extracted from Lactobacillus rhamnosus MLGA, and the effects of different concentrations of WPG on avian β-defensin 9(AvBD9) mRNA expression in immune cells from different tissues 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. The results showed as follows:(1) A trichloroacetic acid(TCA) method was used to extract the WPG from Lactobacillus rhamnosus MLGA, the WPG extraction rate was 3.89%. The products extracted from Lactobacillus rhamnosus MLGA were identified as whole cell wall peptidoglycan by means of electron microscopy observation, amino acid composition analysis and lysozyme digestion tests.(2) WPG from Lactobacillus 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 Lactobacillus rhamnosus-derived WPG,Staphylococcus aureus-derived peptidoglycan down-regulated AvBD9 mRNA expression in chicken PBMCs and splenocytes. Inflammatory cytokines IL-1β, IL-8 and IL-12p40 mRNA expressions in chick PBMCs and splenocytes were not significantly affected by Lactobacillus rhamnosus MLGA WPG(P>0.05), whereas these cytokine expressions in chick PBMCs and splenocytes were significantly suppressed by hydrolysate of Lactobacillus rhamnosus MLGA WPG(P<0.05 or P<0.01). The Lactobacillus rhamnosus-derived WPG and its hydrolysate promoted AvBD9 expression without being accompanied by inflammatory response.(3) The growth of Salmonella enteritidis was significantly inhibited by cell lysates from coculture of PBMCs or splenocytes with Lactobacillus rhamnosus-derived WPG(P<0.01). The antimicrobial effect of cell lysates was increased with the increase of WPG concentrations. Lactobacillus rhamnosus-derived WPG itself and the supernatants from cocultures of chick PBMCs or splenocytes with Lactobacillus rhamnosus-derived WPG showed no inhibitory effect on the growth of Salmonella enteritidis(P>0.05).In conclusion, Lactobacillus rhamnosus MLGA-derived WPG could promote AvBD9 gene expression in chicken immune cells and intestinal tissues in dose- and time-dependent manners. The Lactobacillus rhamnosus-derived WPG and hydrolysate promoted AvBD9 mRNA expression in chicken immune cells without inflammatory response.while the Staphylococcus aureus-derived peptidoglycan suppressed AvBD9 mRNA expression in chicken immune cells.Collectively, the results in the present study indicated that Lactobacillus 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 espression in tissues especiallly in immune cells of chicken. |
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