Host defense in infantile osteopetrosis.

Since infants with malignant osteopetrosis often die from infection at an early age, we studied several aspects of host defense in five such infants. No consistent abnormality was found in cellular or humoral immunity. Monocyte cellular chemotaxis and phagocytosis were normal in four tested infants. However, all four of these infants had decreased intracellular bacterial killing by monocytes. Neutrophil function tests in five infants showed that two had defective bacterial phagocytosis and four had reduced cellular chemotaxis, decreased nitroblue tetrazolium reduction, and decreased intracellular bacterial killing. The severity of the decreased bactericidal capacity of granulocytes did not correlate with the number of circulating immature granulocytes. Our data suggest that abnormal function of circulating monocytes and granulocytes may contribute to impaired host resistance to infection. We postulate that this defect may reflect a more generalized inherited abnormality of phagocytic cells and perhaps osteoclasts that plays a role in the pathogenesis of infantile osteopetrosis.