IFN-γ plays an important role in the host response to a mycobacterial infection. A complete IFN-γ receptor 1 deficiency is a life-threatening condition because it renders patients highly susceptible t o a mycobacterial infection. Several mutations in the IFN-γ receptor and STAT1 gene have been identified in the rare mycobacterial infections. These mutations have partial function of the IFN-γ receptor and similar pathologic features to clinical tuberculosis.

The function of the IFN-γ receptor was evluated in the patients with clinical tuerculosis. In addition, the DNA coding sequence of the IFNgR1 and STAT1 gene was also analyzed in disseminated tuberculosis patients who might have a defective IFN-γ receptor.

The cell surface expression levels of HLA-DR and CD64 in the PMBC after being stimulation with IFN-γ (100Imicro/ml, 1000Imicro/ml) were increased in both controls and patients. However, the rate of increase in both groups was similar. The production of TNF-alpha in the response to stimulation with LPS was higher in the both groups (850.7±687.8 vs. 836.7±564.3 pg/ml). Pretreatment with IFN-γ prior to LPS stimulation resulted infurther increase in TNF-alpha production in the both groups was similar. The known mutations in the IFNgR1 and STAT1 coding sequences were not found in the genomic DNA of patients wit disseminated tuberculosis.

The functional and genetic defects of the IFN-γ receptor were not identified in clinical tuberculosis. This suggests the defective IFN-γ receptor that predispoe patiens to a BCG or NTM infection can not alone account for the cases of clinical tuberculosis.