Neutrophil uptake of vaccinia virus in vitro

We studied human neutrophils for uptake of vaccinia virus. Uptake was determined radiometrically and by electron microscopy. Vaccinia virus was labeled with 14C or 3H, incubated with neutrophils, and quantified in neutrophil pellets in a new radiometric phagocytosis assay. Better results were obtained from assays of [3H]thymidine-labeled virus; uptake increased through 1 hr and then plateaued. Phagocytosis of 3H-labeled Staphylococcus aureus was normal. Uptake of virus was serum dependent. Hexose monophosphate shunt activity was measured by two methods. No 14CO2 from [14C]1-glucose accompanied uptake of vaccinia virus, in contrast to the respiratory burst accompanying bacterial phagocytosis. Electron microscopy showed intact to slightly digested intraphagolysosomal vaccinia virus. Pock reduction assay showed a decrease in viral content due to neutrophils until 6 hr of incubation, when a modest but significant increase was observed. Thus, neutrophil uptake of vaccinia virus is distinguished from bacterial phagocytosis.