Escherichia coli is the leading cause of severe mastitis in dairy farms. As E. coli mastitis is refractory to the hygienic control measures adapted to contagious mastitis, efficient vaccines are in demand. Existing mastitis vaccines, based on the use of killed rough E. coli J5 as the antigen, aim at inducing phagocytosis by neutrophils. We assessed the binding of J5-induced antibodies to isogenic rough and smooth strains along with a panel of mastitis-associated E. coli. Analysis by enzyme-linked immunosorbent assay revealed that antibodies to OmpA or killed J5 bind readily to rough E. coli but poorly to smooth strains. Flow cytometry analysis indicated that immunization with J5 induced antibodies that cross-reacted with rough E. coli strains but with only a small subpopulation of smooth strains. We identified type 1 fimbriae as the target of most antibodies cross-reacting with the smooth strains. These results suggest that the O-polysaccharide of lipopolysaccharide shields the outer membrane antigens and that only fiber antigens protruding at the bacterial surface can elicit antibodies reacting with mastitis-associated E. coli. We evaluated J5-induced antibodies in an opsonophagocytic killing assay with bovine neutrophils. J5 immune serum was not more efficient than preimmune serum, showing that immunization did not improve on the already high efficiency of naturally acquired antibodies to E. coli. In conclusion, it is unlikely that the efficiency of J5 vaccines is related to the induction of opsonic antibodies. Consequently, other research directions, such as cell-mediated immunity, should be explored to improve E. coli mastitis vaccines.

中文翻译：

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大肠杆菌O-抗原多糖对J5诱导的交叉反应抗体的屏蔽作用

大肠杆菌是奶牛场严重乳腺炎的主要原因。由于大肠杆菌乳腺炎对适用于传染性乳腺炎的卫生控制措施无效，因此需要有效的疫苗。现有的乳腺炎疫苗基于使用杀死的粗糙大肠杆菌J5 作为抗原，旨在诱导中性粒细胞的吞噬作用。我们评估了 J5 诱导的抗体与同基因粗糙和平滑菌株以及一组乳腺炎相关大肠杆菌的结合。酶联免疫吸附试验分析表明 OmpA 或被杀死的 J5 的抗体很容易与粗糙的大肠杆菌结合但很难平滑应变。流式细胞术分析表明，J5 免疫诱导的抗体与粗糙的大肠杆菌菌株发生交叉反应，但仅与平滑菌株的一小部分亚群发生交叉反应。我们将 1 型菌毛鉴定为大多数与平滑菌株交叉反应的抗体的目标。这些结果表明脂多糖的 O-多糖屏蔽了外膜抗原，只有在细菌表面突出的纤维抗原才能引发与乳腺炎相关大肠杆菌反应的抗体. 我们在牛中性粒细胞的调理吞噬杀伤试验中评估了 J5 诱导的抗体。J5 免疫血清并不比免疫前血清更有效，这表明免疫并没有提高天然获得的大肠杆菌抗体的效率。总之，J5 疫苗的效率不太可能与调理性抗体的诱导有关。因此，应探索其他研究方向，如细胞介导的免疫，以改进大肠杆菌乳腺炎疫苗。