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.