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Infants with malignant osteopetrosis show impaired monocyte and granulocyte function, leading to reduced bacterial killing and increased infection risk. This suggests a generalized phagocytic cell defect in the disease.
Area of Science:
- Immunology
- Pediatric Hematology/Oncology
- Cell Biology
Background:
- Malignant osteopetrosis in infants frequently leads to early mortality due to infections.
- Understanding host defense mechanisms is crucial for managing these patients.
Purpose of the Study:
- To investigate cellular and humoral immunity in infants with malignant osteopetrosis.
- To identify specific defects in immune cell function contributing to infection susceptibility.
Main Methods:
- Assessed cellular and humoral immunity in five infants with malignant osteopetrosis.
- Performed monocyte function tests including chemotaxis, phagocytosis, and intracellular bacterial killing.
- Conducted neutrophil function tests: phagocytosis, chemotaxis, nitroblue tetrazolium reduction, and intracellular bacterial killing.
Main Results:
- No consistent abnormalities in overall cellular or humoral immunity were found.
- Monocytes showed normal chemotaxis and phagocytosis but decreased intracellular bacterial killing.
- Neutrophils exhibited defective phagocytosis, reduced chemotaxis, and impaired intracellular bacterial killing in some infants.
Conclusions:
- Abnormal monocyte and granulocyte function likely contributes to impaired host resistance in infantile osteopetrosis.
- The observed phagocytic cell defects may stem from a broader inherited abnormality affecting phagocytes and osteoclasts, impacting disease pathogenesis.
Abstract:
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.