INRA, UMR 1282 Infectiologie et Santé Publique, F-37380 Nouzilly, France.
Vet Res. 2012 Feb 13;43(1):14. doi: 10.1186/1297-9716-43-14.
Escherichia coli is a frequent cause of clinical mastitis in dairy cows. It has been shown that a prompt response of the mammary gland after E. coli entry into the lumen of the gland is required to control the infection, which means that the early detection of bacteria is of prime importance. Yet, apart from lipopolysaccharide (LPS), little is known of the bacterial components which are detected by the mammary innate immune system. We investigated the repertoire of potential bacterial agonists sensed by the udder and bovine mammary epithelial cells (bMEC) during E. coli mastitis by using purified or synthetic molecular surrogates of bacterial agonists of identified pattern-recognition receptors (PRRs). The production of CXCL8 and the influx of leucocytes in milk were the readouts of reactivity of stimulated cultured bMEC and challenged udders, respectively. Quantitative PCR revealed that bMEC in culture expressed the nucleotide oligomerization domain receptors NOD1 and NOD2, along with the Toll-like receptors TLR1, TLR2, TLR4, and TLR6, but hardly TLR5. In line with expression data, bMEC proved to react to the cognate agonists C12-iE-DAP (NOD1), Pam3CSK4 (TLR1/2), Pam2CSK4 (TLR2/6), pure LPS (TLR4), but not to flagellin (TLR5). As the udder reactivity to NOD1 and TLR5 agonists has never been reported, we tested whether the mammary gland reacted to intramammary infusion of C12-iE-DAP or flagellin. The udder reacted to C12-iE-DAP, but not to flagellin, in line with the reactivity of bMEC. These results extend our knowledge of the reactivity of the bovine mammary gland to bacterial agonists of the innate immune system, and suggest that E. coli can be recognized by several PRRs including NOD1, but unexpectedly not by TLR5. The way the mammary gland senses E. coli is likely to shape the innate immune response and finally the outcome of E. coli mastitis.
大肠杆菌是奶牛临床乳腺炎的常见病因。已经表明，大肠杆菌进入乳腺腔后，乳腺需要迅速作出反应来控制感染，这意味着早期检测细菌至关重要。然而，除了脂多糖（LPS）之外，人们对乳腺固有免疫系统检测到的细菌成分知之甚少。我们通过使用已鉴定的模式识别受体（PRR）的细菌激动剂的纯化或合成分子类似物，研究了大肠杆菌乳腺炎期间乳腺和牛乳腺上皮细胞（bMEC）感知的潜在细菌激动剂的 repertoire。CXCL8 的产生和白细胞流入牛奶分别是刺激培养的 bMEC 和受挑战的乳房的反应的读数。定量 PCR 显示，培养中的 bMEC 表达核苷酸寡聚化结构域受体 NOD1 和 NOD2，以及 Toll 样受体 TLR1、TLR2、TLR4 和 TLR6，但几乎不表达 TLR5。与表达数据一致，bMEC 被证明对同源激动剂 C12-iE-DAP（NOD1）、Pam3CSK4（TLR1/2）、Pam2CSK4（TLR2/6）、纯 LPS（TLR4）作出反应，但不对鞭毛蛋白（TLR5）作出反应。由于乳腺对 NOD1 和 TLR5 激动剂的反应从未被报道过，我们测试了乳腺对 C12-iE-DAP 或鞭毛蛋白的宫内输注是否有反应。与 bMEC 的反应一致，乳腺对 C12-iE-DAP 有反应，但对鞭毛蛋白无反应。这些结果扩展了我们对牛乳腺固有免疫系统细菌激动剂反应的认识，并表明大肠杆菌可以被几种 PRR 识别，包括 NOD1，但出乎意料的是不能被 TLR5 识别。乳腺感知大肠杆菌的方式可能会影响固有免疫反应，并最终影响大肠杆菌乳腺炎的结果。
