Flagellin (Flg) is a globular protein, found in bacterial flagella, that serves as a pathogen-associated molecular pattern and also serves as a toll-like receptor-5 (TLR5) ligand in vertebrates. Most ligands for TLRs are involved in non-specific effects such as anorexia and hypoactivity in an animal infected by bacteria. However, there is little knowledge on the effects of Flg in birds. Therefore, the purpose of the present study was to determine if intraperitoneal (IP) injection of Flg affects food intake, voluntary activity, cloacal temperature, crop emptying rate, blood constituents, and splenic gene expression of cytokines in chicks (Gallus gallus). The effect of Flg22, an N-terminus fragment of Flg, was also investigated. IP injection of 10 µg Flg significantly increased the splenic gene expression of interleukin-8, interferon-γ (IFN-γ), and tumor necrosis factor-like cytokine-1A, suggesting that Flg activated the innate immune system in chicks. The injection of Flg significantly decreased food intake, voluntary activity, blood glucose concentration, and crop emptying rate, and increased cloacal temperature and plasma concentrations of nitrite, nitrate, and corticosterone. However, the injection of Flg22 only affected the splenic gene expression of IFN-γ, indicating that the full-length of Flg is required for its action. These results suggest that Flg, a ligand for TLR5, is related to non-specific symptoms including anorexia, hypoactivity, increase in body temperature, disturbance of food passage in the digestive tract, and the activation of hypothalamic-pituitary-adrenal axis during bacterial infection in chicks.

鞭毛蛋白（Flg）是一种球形蛋白，存在于细菌鞭毛中，可作为病原体相关的分子模式，也可作为脊椎动物的toll-like receptor-5（TLR5）配体。TLR的大多数配体在被细菌感染的动物中参与非特异性作用，例如厌食和机能减退。但是，关于Flg对鸟类的影响知之甚少。因此，本研究的目的是确定是否腹膜内（IP）FLG的注射影响食物摄取，自主活动，泄殖腔温度，作物排空率，血液成分，而在雏鸡细胞因子的脾基因表达（原鸡）。还研究了Flg22（Flg的N端片段）的作用。IP注射10 µg Flg可以显着提高白细胞介素8，干扰素γ（IFN-γ）和肿瘤坏死因子样细胞因子1A的脾脏基因表达，表明Flg激活了雏鸡的先天免疫系统。注射Flg会显着降低食物摄入，自愿活动，血糖浓度和农作物排空率，并增加泄殖腔温度以及亚硝酸盐，硝酸盐和皮质酮的血浆浓度。然而，注射Flg22仅影响IFN-γ的脾基因表达，表明Flg的全长是其作用所必需的。这些结果表明，TLG5的配体Flg与非特异性症状有关，包括厌食，活动不足，体温升高，