A sensitive procedure for quantifying the phagocytic competence of blood granulocytes

The phagocytic activity of blood granulocytes can be quantitatively assayed by ingestion of opsonised paraffin oil droplets containing the dye "Oil Red-O" (Stossel, T.P., Mason, R.J., Hartwig, J., and Vaughan, M. (1972) J. Clin. Invest. 51: 615-624). We have modified this assay by incorporating [3H]glycerol into the oil droplets which allows a more sensitive and reproducible measurement of the phagocytic competence of blood granulocytes even at very low cell counts. Comparative studies after one day storage of the blood at 4 degrees C is feasible since they retain 84% of the phagocytic capacity measured when isolated from fresh blood.