Effects of Dietary Polyunsaturated Fatty Acids on In Vivo Splenic Cytokine mRNA Expression in Layer Chicks Immunized with Salmonella typhimurium Lipopolysaccharide

Abstract

Effects of dietary polyunsaturated fatty acids (PUFA) on immune responses in poultry have been reported. However, effects on the underlying mechanisms, such as the role of cytokines, have not been documented because the necessary tools were lacking. Recently, primer sets for chicken interleukin (IL)-1β, IL-2, interferon-γ (IFN-γ), myelomonocytic growth factor (MGF), and transforming growth factor (TGF)-β2 have become available. Therefore, in the present study we first examined the in vivo effects of an inflammatory challenge with Salmonella typhimurium lipopolysaccharide (LPS) on cytokine profiles in growing laying-type chicks. Second, we examined whether dietary fat sources affected the observed cytokine profiles. Two hundred forty chicks were assigned in a 2 × 4 factorial design of treatments, with injection with LPS or saline and dietary fat source as factors. Factors were i.v. injection with S. typhimurium LPS or saline (control) and four dietary fat sources: corn oil, linseed oil, menhaden oil, and tallow. Two hours after injection, birds were killed, and their spleens were removed for RNA extraction. Reverse transcription polymerase chain reactions with primer sets for chicken IL-1β, IL-2, IFN-γ, MGF, TGF-β2, and β-actin were performed with RNA samples pooled by pen. The expression of cytokine mRNA was expressed relative to the level of β-actin mRNA. Interleukin-1 (P < 0.001), MGF (P < 0.0001), IL-2 (P < 0.001), and IFN-γ (P < 0.001) mRNA expressions were enhanced by challenge with LPS. Immunization treatment had no effect on TGF-β2 or β-actin expression. Dietary treatment did not affect mRNA expression of IL-1, MGF, IFN-γ, TGF-β2, or β-actin. Interleukin-2 expression in LPS-injected birds that were fed the fish-oil-enriched diet was enhanced (P = 0.05). The present study indicates that in vivo effects of immune challenge on cytokine mRNA expression can be measured in poultry. The observation that mRNA level of IL-2, but not the mRNA levels of IFN-γ or MGF, is enhanced by dietary fish oil at 2 h suggests that dietary PUFA at this moment initially affected naïve T lymphocytes.