INRAE, UMR ISP, 37380, Nouzilly, France; Institut de l'élevage, 75012, Paris, France.
INRAE, UMR ISP, 37380, Nouzilly, France.
J Dairy Sci. 2023 Jun;106(6):4245-4256. doi: 10.3168/jds.2022-22728. Epub 2023 Apr 18.
Bovine mastitis is mainly caused by bacterial infection and is responsible for important economic losses as well as alterations of the health and welfare of animals. The increase in somatic cell count (SCC) in milk during mastitis is mainly due to the influx of neutrophils, which have a crucial role in the elimination of pathogens. For a long time, these first-line defenders have been viewed as microbe killers, with a limited role in the orchestration of the immune response. However, their role is more complex: we recently characterized a bovine neutrophil subset expressing major histocompatibility complex class II (MHC-II) molecules (MHC-II), usually distributed on antigen-presenting cells, as having regulatory capacities in cattle. In this study, our objective was to evaluate the implication of different neutrophils subsets in the mammary gland immunity during clinical and subclinical mastitis. Using flow cytometry, we analyzed the presence of MHC-II neutrophils in blood and in milk during clinical mastitis at different time points of inflammation (n = 10 infected quarters) and during subclinical mastitis, defined as the presence of bacteria and an SCC >150,000 cells/mL (n = 27 infected quarters). Our results show, for the first time, that in blood and milk, neutrophils are a heterogeneous population and encompass at least 2 subsets distinguishable by their expression of MHC-II. In milk without mastitis, we observed higher production of reactive oxygen species and higher phagocytosis capacity of MHC-II neutrophils compared with their MHC-II counterparts, indicating the high bactericidal capacities of MHC-II neutrophils. MHC-II neutrophils are enriched in milk compared with blood during subclinical mastitis but not during clinical mastitis. Moreover, we observed a positive and highly significant correlation between MHC-II neutrophils and T lymphocytes present in milk during subclinical mastitis. Our experiments involved a total of 47 cows (40 Holstein and 7 Normande cows). To conclude, our study opens the way to the discovery of new biomarkers of mastitis inflammation.
奶牛乳腺炎主要由细菌感染引起，会给动物的健康和福利带来重要的经济损失。乳腺炎期间牛奶中体细胞计数（SCC）的增加主要是由于中性粒细胞的涌入，中性粒细胞在消除病原体方面起着至关重要的作用。长期以来，这些一线防御细胞一直被视为微生物杀手，在免疫反应的协调中作用有限。然而，它们的作用更为复杂：我们最近发现了一类在牛中性粒细胞中表达主要组织相容性复合体 II 类（MHC-II）分子的细胞亚群（MHC-II），通常分布在抗原呈递细胞上，在牛中具有调节能力。在这项研究中，我们的目标是评估不同中性粒细胞亚群在临床和亚临床乳腺炎期间对乳腺免疫的影响。我们使用流式细胞术分析了临床乳腺炎不同炎症时间点（n=10 个感染乳区）和亚临床乳腺炎（定义为存在细菌和 SCC＞150,000 个细胞/ml）期间血液和牛奶中 MHC-II 中性粒细胞的存在。我们的研究结果首次表明，在血液和牛奶中，中性粒细胞是一个异质群体，至少包含 2 个可以通过 MHC-II 表达来区分的亚群。在没有乳腺炎的牛奶中，我们观察到 MHC-II 中性粒细胞比 MHC-II 中性粒细胞产生更多的活性氧物质和更高的吞噬能力，表明 MHC-II 中性粒细胞具有很强的杀菌能力。在亚临床乳腺炎期间，与血液相比，MHC-II 中性粒细胞在牛奶中富集，但在临床乳腺炎期间则不然。此外，我们观察到在亚临床乳腺炎期间，MHC-II 中性粒细胞与牛奶中存在的 T 淋巴细胞之间存在正相关且高度显著。我们的实验共涉及 47 头奶牛（40 头荷斯坦奶牛和 7 头诺曼底奶牛）。总之，我们的研究为发现乳腺炎炎症的新生物标志物开辟了道路。
