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Severe, malignant osteopetrosis is a disease characterized by osteoclasts that fail to resorb bone. Serious defects in the ability of white blood cells to eradicate infectious agents confound the clinical course. Defective superoxide generation by neutrophils, monocytes, and lymphocytes contributes to this inability to fight infection. To elucidate the mechanisms resulting in the defective superoxide generation observed in osteopetrotic leukocytes, gene expression, translocation, and phosphorylation of the major components that form the functional NADPH oxidase complex were studied in transformed B-lymphocytes. The expression of the p47 subunit of NADPH oxidase was reduced in B-lymphocytes collected from osteopetrotic patients compared to those from controls. Phosphorylation and translocation of p47 to the cell membrane after PMA stimulation was similar in B-lymphocytes from both patients and normal controls. However, total amount of p47 phosphorylation and translocation was reduced in patient samples. This was further supported by the experiment using p47 antisense oligonucleotide. The other major components of the oxidase (p91, p22, p67) were found to be present at normal levels. Thus, the reduction in p47 expression results in reduced ability to assemble a functional NADPH oxidase complex at the membrane of lymphocytes from osteopetrotic patients. This defect translates into reduced superoxide generation and an increased propensity for infection. |
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