| Abstract
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The aims of this research include: (1) comparison of the agglutination-inducing activity of yeast cell wall products; (2) determination whether mannan rich fraction (MRF), a yeast cell wall product, reduces inflammatory responses of chicken macrophage cell lines exposed to lipopolysaccharide (LPS); (3) identification of mechanisms involved in the reduction of inflammatory responses of chicken macrophage cell lines exposed to LPS by MRF; and (4) to investigate whether MRF can reduce inflammatory responses in vivo. Six yeast cell wall products were examined for their ability to agglutinate Escherichia coli (E. coli) or Salmonella typhimurium (S. typhimurium) cells. The results of the investigation indicated that Product B, Product E, and Product A agglutinated more than 70% of E. coli cells. Product F and Product C agglutinated approximately 69% and 60% of E. coli cells, respectively, while Product D agglutinated only approximately 46% of the E. coli cells. When S. typhimurium was used to test the ability of these yeast products to agglutinate bacterial cells, Product E and Product A agglutinated nearly 70% of S. typhimurium cells. Product F agglutinated approximately 62% cells, and Product B and Product C agglutinated close to 60% of S. typhimurium cells. Product D agglutinated only 46% of S. typhimurium cells. Mannose residues mediated the agglutination of E. coli and S. typhimurium by these yeast products. Infections within the gastrointestinal tract (GIT) with pathogenic strains of E. coli or Salmonella cause fever, diarrhea, anorexia, somnolence, droopy wings, and ruffled feathers in infected chickens and turkeys. These clinical signs are a result of an endotoxin called lipopolysaccharide (LPS), that resides within the outer membrane of these bacteria and stimulates target cells to produce pro-inflammatory cytokines and nitric oxide that mediate clinical signs described above. An in vitro study of the effect of mannan rich fraction (MRF) of yeast Saccharomyces cerevisiae in BioMOS ® on the inflammatory responses of chicken macrophage cell lines (MQ-NCSU and HTC) to LPS was conducted. MRF at 2.5 mg/ml stimulated MQ-NCSU cell proliferation, whereas MRF at 10 mg/ml or higher was toxic to the cells. At the concentration of 2.5 mg/ml, MRF by itself did not induce either MQ-NCSU or HTC chicken macrophage cell lines to produce nitrite or interleukin-6 (IL-6). The nitrite and IL-6 production of MQ-NCSUs and HTCs were significantly increased when cells were stimulated with LPS, but MRF significantly reduced nitrite and IL-6 production of these LPS-stimulated cells. MRF down-regulated inducible nitric oxide synthase (iNOS) and IL-6 gene expression of cell lines stimulated with LPS. An attempt to identify the possible mechanisms involved in the reduction of the inflammatory response by MRF indicated that MRF reduced the expression of LPS receptor toll-like receptor-4 (TLR-4), and possibly activated the transcription factor NF-κB that represses gene expression. It was further investigated whether MRF could also reduce the inflammatory responses in vivo as an in vitro finding often times does not translate to in vivo situation. The results showed that abdominal exudate macrophages from three-week old broiler chickens fed with a basal diet and challenged with enteropathogenic E. coli had a significantly higher nitrite production than similar cells from non-challenged broiler chickens fed with a basal diet. On the other hand, abdominal exudate macrophages of birds challenged with E. coli and fed with a diet supplemented with MRF showed a significantly lower level of nitrite production than cells from challenged birds that were fed with a basal diet. Unexpectedly, macrophages isolated from three weeks old non-challenged broiler chickens fed with MRF produced a slight, but significantly higher level of IL-6 than macrophages from non-challenged birds fed with a basal diet or challenged birds fed with either a basal diet or MRF. MRF was also found to significantly increase body weight gain of E. coli-challenged or n n-challenged broiler chickens compared to the body weight gain of challenged birds fed with a basal diet.
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