Processing of staphylococcus aureus and zymosan particles by human leukocytes measured by flow cytometry

Staphylococcus aureus were labeled with fluorescein‐isothiocytanate (FITC), stained by ethidium bromide (EB), and measured by flow cytometry (FCM). Bacteria were identified by their FITC‐fluorescence and discriminated from the leukocyte cell nuclei by the much higher EB fluorescence and lower coefficient of variation of the latter. Following phagocytosis, both the bacterial FITC‐and EB‐fluorescence decayed. The mean FITC‐fluorescence was reduced about 20% after 15 min and 30–50% after 60 min. Zymosan particles were labeled by FITC and incubated with leukocytes for 15 min. Phagocytes were sorted by FCM and the zymosan particles were liberated by sonication. Their forward angle light scatter was reduced by about 50.6 ± 2.1% and the FITC‐fluorescence by 8.7 ± 1.0% (mean ± SD). The reduced FITC‐fluorescence and light scatter suggests degradation of proteins, and the decay of EB‐fluorescence degradation of DNA, but the specificity remains to be established. By this method phagocytes from a patient with systemic lupus erythematosus seemed to have a selective defect in DNA degradation, whereas phagocytes from a patient with acute myelogenous leukemia had a low capacity to degrade bacterial proteins. This technique offers opportunities for automatic measurements of bacteria and zymosan particle degradation by phagocytes.