Role of degranulation in activation of the respiratory burst in human neutrophils.

ABSTRACT

The neutrophil response to infection and inflammation includes membrane fusion or degranulation and activation of the membranous respiratory burst oxidase. The role of degranulation in the activation of the burst was explored in resting and activated cells. Exposed membrane proteins of intact cells were labeled with impermeant reagents. Phorbol ester-activated neutrophils and enucleated cells which are granule depleted both exhibit increased labeling with [125I]lactoperoxidase over that of resting cells. The binding of antibodies to granule membranes by cells activated with phorbol ester or treated with cytochalasin B and lithium chloride were similarly increased. These data indicate that insertion of granule membrane into the cell membrane occurs during activation and enucleation of neutrophils. Hyperosmolarity, known to inhibit degranulation, also exhibited an inhibitory effect on the respiratory burst oxidase in the presence of phorbol ester or latex. Pre-treatment of cells with phorbol ester followed by an increase in osmolarity, however, still resulted in activation. Temperatures below 17 degrees C abruptly and simultaneously abolish degranulation and activation of the respiratory burst oxidase. Pre-treatment of neutrophils with phorbol ester at 37 degrees C, followed by measurement of oxidase activity at decreased temperatures, on the other hand, revealed a linear Arrhenius plot above and below 17 degrees C. These results suggest that membrane fusion or degranulation is a step in activation of the respiratory burst.