Aerobic responses of mouse macrophages to phagocytosis against Escherichia coli as revealed by microphotometry.

Fluorescence of peritoneal macrophages, which ingested E. coli labelled with N-[7-(dimethylamino)-4-methyl-coumarinyl]-maleimide, was measured with a microfluorometer. The cellular contents of protein and formazan of a monotetrazolium produced by succinate dehydrogenase (SD) activity were assayed with a microspectrophotometer. During phagocytosis, protein increased in 30 min., but was balanced later by self-hydrolysis. SD activity was unchanged for 30 min. and then increased until 2 hrs. Upon removal of bacteria, the fluorescence and protein decreased with time, whereas SD activity increased further for 1 hr. before decrease. This indicates a delayed activation of the enzyme. The cellular ATP content was reduced during phagocytosis and restored to the normal level 3 hrs. after removal of bacteria. Both KCN-sensitive and -insensitive oxygen uptakes increased in phagocytosis. Thus, oxidative metabolism of macrophages is stimulated in phagocytosis and the stimulation can be demonstrated in situ by the microphotometric methods.