Temperature‐dependent formation of vacuolar and canalicular systems in association with degranulation in stimulated neutrophils

Effects of temperature on the morphological changes and degranulation were studied in stimulated neutrophils. Neutrophils were stimulated by formyl‐methionyl‐leucyl‐phenylalanine (FMLP) and cytochalasin B at 4°C, 20°C and 37°C, and they were processed for electron microscopy and biochemical assays of myeloperoxidase (MPO) activity. When neutrophils were stimulated at 4°C, they did not show apparent morphological changes nor release MPO activity. In the cells stimulated at 20°C, there were many cytoplasmic vacuoles, localization of MPO‐positive granules adjacent to the cell membrane and around the vacuoles, MPO‐positive materials in the cavity of the vacuoles, and slightly decreased numbers of granules. They released moderate amounts of MPO activity. The neutrophils at 37° C showed formation of small vacuoles and canaliculi and a marked decrease in the number of MPO‐positive granules indicative of degranulation, and they released increased amounts of MPO activity. There were MPO‐positive materials on the membrane and in the cavity of the vacuoles. Ruthenium red staining showed that the vacuoles were formed open outside the cell. These results indicate that the vacuolar systems are involved in degranulation in stimulated neutrophils and that their formation is dependent on temperature.