Resazurin reduction as a function of respiratory burst in bovine neutrophils.

OBJECTIVE: To determine whether the respiratory burst of neutrophils from bovine blood and milk can be analyzed by use of a fluorometric resazurin reduction assay.

SAMPLE POPULATION: Neutrophils were obtained from EDTA-anticoagulated blood of 7 dairy cows. Neutrophils also were isolated from milk samples of a cow intramammarily challenge exposed with Escherichia coli lipopolysaccharide.

PROCEDURE: The respiratory burst of neutrophils was analyzed in parallel, using the conventional luminol-enhanced luminometric procedure and a novel fluorometric procedure with resazurin as the fluorogenic substrate. Opsonized zymosan and phorbol myristate acetate were used as stimulants. The mechanism of the fluorescent response was analyzed, using metabolic inhibitors to various cell functions. Luminometry and fluorometry were carried out in parallel, using microtitration tray-reading instruments.

RESULTS: Stimulation of neutrophils induced resazurin reduction to resorufin and a fluorescent response. The luminescent response was transient, but the fluorescent response (build-up of fluorescent resorufin) was cumulative. Therefore, a single end-point measurement can be used for the fluorometric assay.

CONCLUSIONS: The proposed fluorometric microtitration tray technology is simple and has a high throughput capacity. The fluorometric and luminometric assays seem to have similar potential in the analysis of phagocyte functions.