Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) are the most prevalent pathogens to induce mastitis. The pathogenesis of infections induced by E. coli is sophisticatedly modulated by lipopolysaccharide (LPS), LPS binding protein, membrane CD14 (mCD14), and soluble CD14 (sCD14). In the first study, administration of recombinant bovine sCD14 (rbosCDl4) significantly reduced the fatality of LPS challenged mice and the severity of mouse mastitis in terms of clinical signs, bacterial load, and TNF-alpha production. Before investigating the potential of this strategy in dairy cows, endogenous sCD14 in milk was characterized. Based on the data of 396 quarters, the milk concentration of sCD14 was 6.67 +/- 0.44 mug/ml. The stages of lactation affected the concentration of sCD14 in milk, which was higher in transitional milk (0--4 days postpartum). Milk sCD14 also increased during an intramammary LPS challenge, which paralleled with SCC increase. The protective effect of sCD14 on bovine E. coli mastitis was then investigated. It was shown that rbosCDl4 sensitized the mammary gland to recruit leukocytes in response to LPS. To prove that the early recruitment of leukocytes plays a role in preventing intramammary E. coli infections, E. coli mastitis was induced in 9 dairy cows with or without 100 mug rbosCD14. Quarters challenged with E. coli plus rbosCD14 had a more rapid recruitment of neutrophils, a faster clearance of bacteria, reduced concentrations of TNF-alpha and IL-8 in milk, and reduced clinical symptoms than quarters injected with saline. / For S. aureus mastitis, a newly designed trivalent whole-cell vaccine being composed of the most dominant serotypes (T5, T8, and T336) was evaluated. The vaccine was immunized with or without either one of the two adjuvants, aluminum hydroxide (ALUM) and Freund's incomplete adjuvant (FICA). The vaccine, with or without the presence of adjuvants, increased antigen-specific IgG1, IgG2, but not IgM, in serum. However, all formulations only had limited effects on lymphocyte subsets, interferon (IFN)-gamma mRNA expression, and neutrophil phagocytosis in comparison with the control. / Taken together, the results indicated that increasing the concentration of sCD14 in milk might be a potential strategy to prevent or reduce severity of E. coli mastitis. On the other hand, both ALUM and FICA did not augment the immune responses when formulated with trivalent vaccine. A more immunostimulatory adjuvant will be required to improve the efficacy of the novel trivalent vaccine against S. aureus mastitis.

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