Extracellular Stimulation of Intracellular Killing

Abstract

Two main approaches have been used to investigate the intra-cellular killing of micro-organisms by monocytes. The first is microbiological, the killing by phagocytic cells being estimated from the decrease in the number of viable cell-associated bacteria during incubation of phagocytes together with bacteria (Cohn & Morse 1959; Quie et al. 1967). The disadvantage of this widely used method is that the rate of intracellular killing is dependent on the continuous ingestion of new bacteria, and therefore the actual intracellular killing cannot be measured accurately. The second approach is biochemical, being based on measurement of the ‘metabolic burst’ during phagocytosis. The conversion of O2 into the bactericidal agents 2 - and H2O2 during the phagocytosis of particles by granulocytes and monocytes is taken as an indirect measure of the killing capacity of the phagocytic cells (Sbarra & Karnovsky 1959; for review see Klebanoff 19 79). However, this approach does not elucidate the intracellular killing itself because in biochemical assays the metabolic burst is measured during the continuous ingestion of inert particles or bacteria.