Enzymes of leukocyte oxidative metabolism in Down's syndrome

Enzymes of importance for oxygen dependent leukocyte killing of microorganisms were studied in 14 patients with Down's Syndrome (DS) and 10 controls. As has been reported previously for other cell types, the level of CuZn superoxide dismutase (SOD) was 50% higher in polymorphonuclear leukocytes (PMN) from DS patients than from the controls. The amount of SOD was extremely low in the PMNs from controls, i.e. only about 6% of the levels in other human tissues. The levels of catalase and of the Mn dependent SOD were normal. The myeloperoxidase (MPO) activity of DS PMNs was only 59% of that of the control cells. Previously reported increased levels of CuZnSOD and GSH peroxidase in erythrocytes and CuZnSOD in lymphocytes were confirmed. The increased levels of SOD in DS phagocytes provide a possible partial explanation for previous reports of defective killing of S. aureus in DS. In addition, the MPO deficiency impairs the H2O2-halide-MPO system, which is of particular importance for fungal killing, e.g. of C. albicans, which has also been reported to be deficient in DS. The findings may thus explain some of the mechanisms underlying the increased susceptibility to certain infections in DS.