Mutagenesis of immunoglobulin-like domains from the extracellular human interferon-gamma receptor alpha chain and their recognition by neutralizing antibodies monitored by surface plasmon resonance technology

In a novel form of IFN-gamma receptor 1 deficiency, cell surface receptors fail to bind IFN-gamma

Complete IFN-gamma receptor ligand-binding chain (IFNgammaR1) deficiency is a life-threatening autosomal recessive immune disorder. Affected children invariably die of mycobacterial infection, unless bone marrow transplantation is undertaken. Pathogenic IFNGR1 mutations identified to date include nonsense and splice mutations and frameshift deletions and insertions. All result in a premature stop codon upstream from the segment encoding the transmembrane domain, precluding cell surface expression of the receptors. We report herein two sporadic and two familial cases of a novel form of complete IFNgammaR1 deficiency in which normal numbers of receptors are detected at the cell surface. Two in-frame deletions and two missense IFNGR1 mutations were identified in the segment encoding the extracellular ligand-binding domain of the receptor. Eight independent IFNgammaR1-specific mAb's, including seven blocking antibodies, gave recognition patterns that differed between patients, suggesting that different epitopes were altered by the mutations. No specific binding of (125)I-IFN-gamma to cells was observed in any patient, however, and the cells failed to respond to IFN-gamma. The mutations therefore cause complete IFNgammaR1 deficiency by disrupting the IFN-gamma-binding site without affecting surface expression. The detection of surface IFNgammaR1 molecules by specific antibodies, including blocking antibodies, does not exclude a diagnosis of complete IFNgammaR1 deficiency.

Variable region cDNA sequences and characterization of murine anti-human interferon gamma receptor monoclonal antibodies that inhibit receptor binding by interferon gamma

Murine monoclonal antibodies (mAbs) are described that recognize the extracellular human interferon gamma receptor alpha-chain (IFN gamma R) and inhibit the binding to it of interferon gamma. The inhibitory activities (IC50s) of these mAbs, quantified by radioimmunoassay using native receptor on human Raji cells, lie in the range 0.5-24 nM, whereas their relative affinities for the immobilised recombinant extracellular receptor, determined using surface plasmon resonance technology, are in the range 0.6-40.9 nM. Nine mAbs derived from one immunization, were shown by variable region cDNA sequencing to be clonally related, with mAb A6 from this group showing the highest affinity for the receptor. Another two mAbs, gamma R38 and gamma R99, derived from a separate immunization, are clonally unrelated to each other and to those in the A6 family. From the V-region sequences, the L-chains of mAbs A6, gamma R38 and gamma R99 were shown to belong to the V kappa 34C, V kappa 34C and V kappa 1 families, whereas the H-chains belong to the 3069, J606 and J558 families, respectively. The mAbs A6 and gamma R38 recognize overlapping epitopes on the N-terminal Ig-like domain of the IFN gamma R, whereas the gamma R99 epitope is located largely in the membrane proximal Ig-like domain. Sequence comparisons with Ig structures solved by X-ray diffraction allowed deductions concerning likely CDR canonical conformations. These studies provide essential information for crystallographic and mutagenesis experiments aimed at understanding the molecular basis of the interactions of these mAbs with the extracellular IFN gamma R.