Phagocytic function in Down syndrome--II. Bactericidal activity and phagocytosis.

Bactericidal capacity was investigated to delineate the impairment of phagocytic function. Fourteen individuals with Down syndrome and fifteen matched institutionalised controls were studied. A non-matched comparison normal group was also evaluated, representing a non-institutionalised young adult population. Neutrophil bactericidal capacity was impaired in institutionalised subjects, the defect being most apparent in Down syndrome. Monocyte bactericidal capacity was identical in institutionalised and non-institutionalised subjects. Humoral functions revealed no differences. Neutrophil phagocytosis was diminished in institutionalised individuals, Down syndrome subjects being the least effective. Monocytes had normal phagocytosis, but opsonisation was defective in both the Down syndrome and matched institutionalised groups. Neutrophils were more efficient at phagocytosis than monocytes. No physiologically significant differences were noted in neutrophil or monocyte intracellular killing.