Detection of lactoferrin and myeloperoxidase release from single neutrophils by a protein A plaque assay

A haemolytic plaque assay was adopted to detect release of lactoferrin and myeloperoxidase (MPO) from single neutrophils. Target erythrocytes coated with protein A were bound as a monolayer by poly-L-lysine to the surface of a plastic dish. Secreted lactoferrin and MPO induced plaque formation dependent on the reaction with complement and specific antiserum producing lysis of the protein-A-coated sheep red blood cells. Lactoferrin was found to be released spontaneously from a fraction of neutrophils while MPO was released only after phagocytosis, reflecting different mechanisms for degranulation of MPO-containing azurophil and lactoferrin-containing specific granules.