A Functional Differentiation of Human Neutrophil Granules: Generation of C5a by a Specific (Secondary) Granule Product and Inactivation of C5a by Azurophil (Primary) Granule Products

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Abstract
During phagocytosis of latex particles human neutrophils not only release a serum activator that generates the chemotactic C5 fragment, C5a, by complement activation, but these cells also release a product that destroys the chemotactic activity of C5a. These separate neutrophil products, however, are released sequentially by neutrophils during phagocytosis with the serum activator appearing more rapidly in incubation media. Chemotactic activity is generated optimally in serum by post-phagocytic media at pH 7.2 to 7.4, whereas C5a inactivation occurs both at neutral pH and at a more acid pH, 6.2 to 6.4. Studies in which the azurophil (primary) granules and specific (secondary) granules are separated from neutrophil lysates by sucrose density centrifugation show that the serum activator is contained in specific granules whereas C5a inactivators are restricted to the azurophil granules. Gel filtration chromatography of lysates of purified granule preparations indicates that the serum activator contained in specific granules is a large molecule (m.w. greater than 150,000), and that there are at least two C5a inactivators associated with the azurophil granules, with estimated m.w.'s of 65,000 and 30,000. Isoelectric focusing of azurophil granule lysates also indicates at least two separate C5a inactivators. It is evident that mediators contained in the specific and azurophil neutrophil granules may have functionally opposing roles once released by the cells. These mediators, which effect the generation or inactivation of C5a, have different pH optima of activity and distinct kinetics of release from neutrophils and together may contribute to the self-limited amplification and localization of acute inflammatory responses.