Conjugated linoleic acids alleviate infectious bursal disease virus-induced immunosuppression in broiler chickens

The immunoregulatory actions of conjugated linoleic acid (CLA) of relevance to viral disease pathogenesis and immune responses were investigated. To test the hypothesis that CLA ameliorates immunosuppression, we developed a viral challenge model by infecting chickens with infectious bursal disease virus (IBDV). After 14 d of dietary supplementation with either soybean oil or CLA, half of the chickens in each group were challenged with IBDV. We examined the effect of CLA on the development of lesions (i.e., lymphoid depletion and necrosis) and observed the immune responses against IBDV. The IBDV infection depleted lymphocytes in the medullary area and significantly stimulated interferon (IFN)-γ and IL-6 mRNA relative expression of bursa (P < 0.05) compared with the uninfected bursa. Compared with the CLA diet, lymphocytes depletion was more accentuated in chickens fed the control diet, whereas IFN-γ and IL-6 mRNA relative expression were upregulated (P < 0.05). Additionally, histopathological examination of the bursa revealed that the pathological changes tended to be more severe in infected chickens fed the control diet, which also significantly decreased (P < 0.05) on lymphocyte proliferation. Significant interactions were found between infection and diets for lymphocyte proliferation, antibody titers, and IFN-γ mRNA relative expression (P < 0.05). The results of this study indicate that dietary CLA enhanced immune function in chickens, particularly those of the IBDV-immunosuppressive status. Furthermore, at the molecular level, the immunoregulatory functions of CLA on chickens are attributable mainly to the antiinflammatory properties of CLA and are mediated, at least in part, through suppressing IBDV-specific proinflammatory cytokines mRNA relative expression.