Human IFNAR2 deficiency: Lessons for antiviral immunity

Abstract

Type I interferon (IFN-α/β) is a fundamental antiviral defense mechanism. Mouse models have been pivotal to understanding the role of IFN-α/β in immunity, although validation of these findings in humans has been limited. We investigated a previously healthy child with fatal encephalitis after inoculation of the live attenuated measles, mumps, and rubella (MMR) vaccine. By targeted resequencing, we identified a homozygous mutation in the high-affinity IFN-α/β receptor (IFNAR2) in the proband, as well as a newborn sibling, that rendered cells unresponsive to IFN-α/β. Reconstitution of the proband's cells with wild-type IFNAR2 restored IFN-α/β responsiveness and control of IFN-attenuated viruses. Despite the severe outcome of systemic live vaccine challenge, the proband had previously shown no evidence of heightened susceptibility to respiratory viral pathogens. The phenotype of IFNAR2 deficiency, together with similar findings in STAT2-deficient patients, supports an essential but narrow role for IFN-α/β in human antiviral immunity.

Figure 1. Failure of IFN-α/β antiviral response.

(A) Meningoencephalitis on cortical biopsy. Cortical inflammatory cell nodular infiltrate (left) with marked microglial activation (CD45 staining, middle) and patchy dural inflammation (right). Scale bars 100µm (B) Patient fibroblasts supported the formation of large plaques by parainfluenza 5 and Bunyamwera viruses deleted for IFN-α/β antagonists (PIV5ΔC, BUNΔNSs). Scale bar 1cm (C) Failure of IFN-α to inhibit wild-type (WT) PIV5 replication in patient fibroblasts, revealed by immunofluorescence staining of viral antigen. Scale bars 50µm. (D) Immunoblot showing absence of antiviral protein (MXA and IFIT1/ISG56) induction by IFN-α (representative of n=3 experiments). (E) Absent transcriptional response to IFN-α and IFN-β but preserved IFN-γ response in patient cells, assessed by microarray; red dots represent significantly differentially expressed probes (≥ 2-fold, adj. P<0.01, n=3 replicates). Exact P values are reported in supplemental datasets S1-3. Patient = patient II.1 (see Figure 3).

Figure 2. Absence of IFN-α/β signaling but preserved IFN-γ signaling.

(A) Schematic of IFN-α/β and IFN-γ signal transduction. (B) Absent tyrosine phosphorylation of TYK2/JAK1/STAT1/STAT2 in response to IFN-α. (C) Normal tyrosine phosphorylation of JAK1/STAT1 in response to IFN-γ(C). Data are representative of n=3 experiments. Patient = patient II.1 (see Figure 3).

Figure 3. Autosomal recessive IFNAR2-deficiency.

(A) Capillary sequencing of IFNAR2 revealed variant c.A311del was homozygous in patient II.1, resulting in a frameshift mutation p.E104fs110X, heterozygous in both parents, and homozygous in a newborn sibling, II.2. (B) A311del is predicted to truncate all protein isoforms of IFNAR2 at the first N-terminal extracellular domain (ECD). (C) Absent IFNAR2 expression in fibroblasts of the proband by immunoblot with an antibody against C-terminal IFNAR2 (representative of n=3 experiments).

Figure 4. IFNAR2 complementation restores IFN-α/β responses.

(A) Stable expression of WT IFNAR2 or null control by lentiviral transduction in patient fibroblasts restored: (B) STAT1 tyrosine phosphorylation; (C) ISG induction (representative immunoblots of n=3 experiments); (D) Control of IFN-attenuated viruses parainfluenza 5 VΔC (PIV5VΔC) and Edmonton strain measles (MeV) in plaque assays; and (E) overnight IFN-α inhibition of Enders mumps vaccine (MuV), PIV3 and PIV5 by immunofluorescent detection of viral protein. Scale bars 200μm, Patient = patient II.1.