Pulmonary infection with nontuberculous mycobacteria (NTM) in previously healthy human immunodeficiency virus-seronegative individuals is difficult to treat. Recently, functional interferon (IFN)-γ deficiency has been identified in individuals susceptible to this disease. Treatment with inhaled IFN-γ for NTM pulmonary disease associated with functional IFN-γ deficiency has not been previously described.

In this study, the IFN-γ pathway was characterised in an individual who had progressive NTM pulmonary infection, despite appropriate multidrug antibiotic therapy, and 10 healthy controls. Levels of IFN-γ and tumour necrosis factor-α in whole blood were assessed before and after incubation with lipopolysaccharide, heat-killed Escherichia coli, heat-killed Staphylococcus aureus and phorbol myristate acetate/ionomycin. The coding regions of interleukin (IL)-12, IL-18 and the IL-12 receptor were sequenced using nested primers. IFN-γ1b (100 µg·dose⁻¹) was administered to the affected individual by ultrasonic nebuliser 3 days·week⁻¹ for 3 months.

In vitro whole blood production of IFN-γ with and without physiological stimuli was consistent with functional IFN-γ deficiency in the affected individual. There was no evidence of mutation in the coding regions of IL-12p35, IL-12p40, IL-12Rβ1 and IL-18 in the affected individual. Treatment with inhaled IFN-γ resulted in rapid and sustained clearance of the organism from the airways and stabilisation of lung function.

In conclusion, inhaled interferon-γ can be effective for the treatment of nontuberculous mycobacteria pulmonary disease associated with functional interferon-γ deficiency.