A total of 3 × 5 ml heparin blood tubes were collected from each of five donors, and individual tubes were either processed immediately or kept at RT for 6 or 24 h. Whole blood and PBMCs were analysed by fluorescence flow cytometry, using a cocktail of antibodies to CD3, CD4, CD8, CD56, CD14 and CD16. Dead cells were excluded with NIR viability dye. The percentage of neutrophils, identified by side scatter and expression of CD16, within live cells was calculated for (A) whole blood and (B) PBMCs. Each donor is indicated by a different colour. Data were analysed with a one-way repeated measures ANOVA with post-hoc Tukey’s tests and P values indicating significant differences between the timepoints are shown. (C–E) Aliquots of PBMCs were cytospun, stained with modified Giemsa and photographed. Green arrows indicate neutrophils with typical mature nuclear morphology in the 6 and 24 h samples.