A Novel Mutation 774del4 in IFNGR1, Which Produces Truncated Form of Interferon γ Receptor 1, Causes a Dominant-Negative Effect on Interferon γ Signal Transduction.

Patients with interferon γ receptor 1 (IFNγR1) deficiency are characterized by disseminated Bacilli Calmette-Guérin (BCG) infections and severe non-tuberculosis mycobacterium infections, and show remarkable genetic heterogeneity. It is known as one of inherited immunodeficiency disorders with recessive or dominant form. So far known dominant forms of IFNγR1 deficiency are associated with heterozygous mutation in the intracellular domain of IFNγR1, among of which 818del4 is known as a major mutation in IFNGR1, leading to frameshift and premature stop codon. We describe here a novel heterozygous IFNGR1 mutation in a patient with recurrent mycobacterium infections, resulting in impairment of receptor degradation. The proband, a 12-year old Japanese girl, developed multiple osteomyelitis due to M. avium infection. She had suffered from BCG lymphadenitis, which occurred 2 months after BCG vaccination, for 3 years. DNA sequence analysis of IFNGR1 demonstrated that the patient had a heterozygous mutation 774del4, producing a truncated protein lacking intracellular component of IFNγR1. IFNγR1 was overexpressed on the surface of CD14-positive cells in the peripheral blood of the patient, and STAT1 phosphorylation was partially defected in response to high dose IFN-γ stimulation. Impaired TNF-α production in response to IFN-γ stimulation was also observed. T cells from the patient presented decreased IFN-γ production in response to IL-12 stimulation.

In order to define the characterization of this truncated form of IFNγR1, we cloned 774del4 and 818del4 mutations as well as the wild-type into mammalian expression vector. These constructs were transfected into HEK293 cells. Cycloheximide (CHX) treatment enabled detection of IFNγR1 expression by flow cytometry and Western blot analysis. In contrast to the wild-type IFNγR1 protein, which rapidly disappeared after CHX treatment, 774del4 mutant protein was stably retained on the cell surface as was observed in 818del4 mutant. These observations suggest that 774del4 mutant causes overexpression of dominant-negative form of IFNγR1 on the cell surface through impairment of receptor degradation.