A rapid, direct assay to measure degranulation of bovine neutrophil primary granules

A direct, rapid, quantitative colorimetric assay to determine neutrophil primary granule degranulation was adapted for use with bovine neutrophils. The assay measures the exocytosis of myeloperoxidase (MPO) using 3,3',5,5'-tetramethylbenzidine as a substrate. The assay was validated by evaluating the effects of various stimulants and inhibitors of degranulation, the kinetics of primary granule exocytosis, and comparing the total myeloperoxidase content of neutrophils obtained from calves and adults. The results demonstrate that the assay is capable of detecting important differences that may occur in degranulation of bovine neutrophil primary granules and in total neutrophil myeloperoxidase content.