Quantitative evaluation of plasma-opsonizing activity from the lag period of phagocytosis-connected oxygen consumption by leukocytes in whole blood.

The lag period preceding the burst of oxygen consumption by phagocytes was measured with an oxygen electrode after the addition of unopsonized zymosan in CO-treated and diluted whole blood. The duration of the lag period correlated with the phagocytic index (r = 0.98, p < 0.001). The phagocytic index was defined as the mean number of zymosan particles per phagocyte. The lag period was termed opsonizing time and used for evaluation of plasma opsonizing activity. The opsonizing time was found to be inversely related to the plasma concentration used (< 15%) and was independent of phagocyte concentration. Magnesium ions were required throughout the opsonizing time, but calcium ions were essential only during the initial phase, indicating that the alternative complement pathway plays a major role in the observed opsonizing time. The mean opsonizing times in blood from normal adults and newborn infants were 5.6 +/- 0.7 min (n = 7) and 9.1 +/- 0.7 (n = 4), respectively. The opsonizing time, expressed as its reciprocal value, correlated significantly with phagocytic index, CH50 activity, and immunochemically assayed C3, but not C4, concentration in plasma.