IFN-γ Enhances Osteoclast Generation in Cultures of Peripheral Blood from Osteopetrotic Patients and Normalizes Superoxide Production

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Abstract
Interferon-γ (IFN-γ) treatment increases osteoclastic bone resorption in vivo in patients with malignant osteopetrosis (OP). The treatment effect was studied in vitro in osteoclasts generated by culturing peripheral white blood cells (PWBC) from OP patients and normal human control subjects. Osteoclasts were treated with or without IFN-γ prior to the end of the culture period. Osteoclasts from normal subjects were large in size (161 +/- 18 μm in diameter) with >10 nuclei per osteoclast. These cells showed intense staining for tartrate-resistant acid phosphatase (TRAP), expressed abundant calcitonin receptors (CTR), and formed numerous resorption pits on bovine bone slices, indicative of authentic osteoclasts. In contrast, similarly cultured osteoclasts from OP patients were smaller in size (18 +/- 3 μm in diameter), with 2-3 nuclei per osteoclast, and stained lightly for TRAP. However, IFN-γ treatment of osteoclasts from OP patients resulted in the formation of larger osteoclasts (171 +/- 33 μm in diameter) with >10 nuclei per cell, similar in appearance to osteoclasts from normal subjects. IFN-γ stimulation increased the intensity of TRAP staining (p < 0.0001) to levels near that of the normal osteoclasts. Unstimulated osteoclasts from 6 OP patients had a significantly lower baseline level of superoxide production, as measured by nitroblue tetrazolium reduction (p < 0.0001), compared with normal osteoclasts. IFN-γ markedly increased (p < 0.0001) superoxide production. Whereas there was a 3-fold increase in superoxide generation in OP patients' osteoclasts, osteoclasts from control subjects had only a small and insignificant increase in superoxide production after IFN-γ treatment.