Dairy cow mastitis is a common bacterial infectious disease which seriously threatens the development of the dairy cow industry. Previous studies have found that increased IFN-γ expression in dairy cows makes dairy cows more susceptible to mastitis, but the underlying mechanism is still not known. In this study, we utilized the in vitro bovine mammary epithelial cells (BMECs) model to explore the molecular mechanism via transcriptome sequencing technology, immunofluorescence, and Western blotting. It was found that IFN-γ promoted the adhesion and invasion of Staphylococcus aureus to BMECs through increasing the expression of TLR4-mediated CCL5 in BMECs. IFN-γ increased the activity of arginase II and reduced the level of arginine in cells, while the addition of arginine inhibited the expression of TLR4 and CCL5. An invasion experiment in mice further validated that IFN-γ treatment significantly increased the bacterial load in mammary glands and blood. However, the colonization and diffusion of S. aureus were interestingly decreased after Arg supplement. These data reveal that increased IFN-γ reduces arginine levels and activates TLR4-CCL5 signaling, leading to enhanced susceptibility of BMECs to S. aureus. Our findings are helpful to understand the pathogenesis of dairy cow mastitis and provide a theoretical basis for improvement of mastitis resistance in dairy cows.

奶牛乳腺炎是一种常见的细菌性传染病，严重威胁奶牛产业的发展。先前的研究发现，奶牛中 IFN-γ 表达增加会使奶牛更容易患乳腺炎，但其潜在机制尚不清楚。在这项研究中，我们利用体外牛乳腺上皮细胞（BMECs）模型，通过转录组测序技术、免疫荧光和蛋白质印迹来探索分子机制。发现IFN-γ促进金黄色葡萄球菌的粘附和侵袭通过增加 BMECs 中 TLR4 介导的 CCL5 的表达对 BMECs 产生影响。IFN-γ增加了精氨酸酶II的活性，降低了细胞中精氨酸的水平，而精氨酸的加入抑制了TLR4和CCL5的表达。在小鼠中进行的入侵实验进一步证实了 IFN-γ 治疗显着增加了乳腺和血液中的细菌负荷。然而，在补充 Arg 后，金黄色葡萄球菌的定植和扩散有趣地降低了。这些数据表明，增加的 IFN-γ 会降低精氨酸水平并激活 TLR4-CCL5 信号传导，导致 BMECs 对金黄色葡萄球菌的敏感性增强. 本研究结果有助于了解奶牛乳腺炎的发病机制，为提高奶牛乳腺炎抵抗力提供​​理论依据。