The use of frozen monocytes in phagocytosis studies

Human monocytes were isolated from peripheral blood by Lymphoprep density-gradient centrifugation and adherence to fibronectin. The cells were loosened by ethylene-diamino-tetra-acetate (EDTA), frozen by different freezing methods, thawed, washed and compared to unfrozen cells. After freezing, thawing and washing, cell recovery was calculated and found to vary with the freezing procedure. The best result was about 76% cell recovery. No morphological differences were observed between unfrozen and frozen cells. The experiments also showed that the percentage of cells that attached or phagocytized IgG-opsonized erythrocytes (E-IgG) via the Fc-receptor was unaltered after freezing. Neither was there any difference between unfrozen and frozen monocytes with respect to their ability to phagocytize latex particles. There was no significant difference in reactivity between monocytes frozen for one day and those frozen for six weeks.