Abstract: Echinacea is an important immune enhancer, which is often used as a substitute for antibiotic as feed additive, however, its immune mechanism needs further study. The purpose of this study was to investigate the effects of Echinacea on enhancing immune function of immunosuppressed chicken by regulating TLR4-NF-κB pathway. A total of 120 7-day-old chicken were randomly divided into 4 groups:the control group, cyclophosphamide group, Echinacea group and Echinacea + cyclophosphamide group (combined group), respectively. The chickens of cyclophosphamide group and combined group were chest muscles injected with saline compound cyclophosphamide solution (80 mg·kg^-1) for 3 consecutive days,while the control group and Echinacea group were injected with the same amount of normal saline for 3 days. The chickens of Echinacea and combined groups were fed with basal diet which containing Echinacea herb powder (1%) daily, and the rest of the chickens were fed with the basal diet. All the chikens were weighed and recorded every day. The experiment lasted for 21 days. At the end of the experiment, the changes of body weight and spleen index were analyzed, and the mRNA and protein expression levels of inflammatory factors (NF-κB, IκB, IL-2, IL-4, IL-6, TNF-α, IFN-γ) and TLR family (TLR2, TLR4, TLR7, MyD88) were detected. The results showed that Echinacea improved the growth performance of chickens, while cyclophosphamide inhibited the growth of chickens. The spleen coefficient of chickens in cyclophosphamide group was significantly lower than that in other groups (P<0.05), while the pathological changes of spleen tissue sections in the cyclophosphamide group were obvious, and the pathological changes in the combined group were relieved. Compared with the control group, the mRNA levels of NF-κB, IL-2, IL-4, IL-6, IFN-γ, TLR2, TLR4, TLR7 and MyD88 in cyclophosphamide group were significantly decreased to varying degrees (P<0.05, P<0.01 or P<0.001). Compared with the cyclophosphamide group, the above genes(except TLR7) significantly increased in the combined group(P<0.05, P<0.01 or P<0.001). In addition, the supplementation of Echinacea significantly increased the expression levels of inflammatory factors and TLR family-related proteins. The results indicated that Echinacea enhanced the immune function of immunosuppressed chickens by regulating TLR4-NF-κB pathway.

Key words: Echinacea, cyclophosphamide, immunosuppression, NF-κB, TLR4