Recurrent rhinovirus infections in a child with inherited MDA5 deficiency

Lamborn, Ian T.; Jing, Huie; Zhang, Yu; Drutman, Scott B.; Abbott, Jordan K.; Munir, Shirin; Bade, Sangeeta; Murdock, Heardley M.; Santos, Celia P.; Brock, Linda G.; Masutani, Evan; Fordjour, Emmanuel Y.; McElwee, Joshua J.; Hughes, Jason D.; Nichols, Dave P.; Belkadi, Aziz; Oler, Andrew J.; Happel, Corinne S.; Matthews, Helen F.; Abel, Laurent; Collins, Peter L.; Subbarao, Kanta; Gelfand, Erwin W.; Ciancanelli, Michael J.; Casanova, Jean-Laurent; Su, Helen C.

The MDA5 protein encoded by IFIH1 consists of N-terminal tandem caspase activation recruitment domains (CARD) and a C-terminal domain (CTD), which surround a central tripartite helicase core (Wu et al., 2013) . MDA5 forms a "C"-shaped ring encircling (ds)RNA, such that its monomers stack together along the (ds)RNA stem to form long filaments necessary for recognition of viral RNA. Lysine at 365 is located in the Hel1 domain of the helicase core ( Fig. 2 B) , where it interacts with the 2'-hydroxyl group of ribose in the target RNA backbone (Wu et al., 2013) . Substitution with glutamic acid introduces a negative charge that is predicted to abolish the protein-nucleic acid interaction and MDA5 These were classified as positive single-stranded RNA virus, negative single-stranded RNA virus, double-stranded DNA virus, or bacteria as indicated in the adjacent symbol key. (B) RT-PCR molecular typing of RNA isolated from nasopharyngeal samples, using primer sets that preferentially amplify the indicated HRV species. Patient's samples a to h, as indicated in A, were collected between 2 and 4 yr of age. Sample a was negative for respiratory pathogens and h positive for influenza A. Purified HRV-B14 and -A16 virus stocks, and a sample from a different subject having respiratory symptoms but negative for HRV/ enterovirus, were also tested. Results are representative of three repeats. (C) Phylogenetic tree based on nucleotide sequences of 5′UTR of HRV isolates showing evolutionary relationship of the patient's samples to closest serotypes and representative HRV species. oligomerization ( Fig. 2 C) . Consistent with our prediction, either before or after induction by IFN-α treatment, the endogenous MDA5 protein in homozygous mutant patient cells was expressed at levels comparable to those in cells from healthy controls or heterozygous or homozygous wild-type family members (Fig. 2 D and not depicted) . Levels of endogenous RIG-I or MAVS proteins were unaffected (Fig. 2 D) . However, when overexpressed in cells that lack endogenous protein, mutant MDA5 failed to bind to a synthetic MDA5 ligand, poly(I:C) (Fig. 2 E; Gitlin et al., 2006; Kato et al., 2006) .