Large-scale mutational analysis identifies UNC93B1 variants that drive TLR-mediated autoimmunity in mice and humans.

Nucleic acid-sensing Toll-like receptors (TLR) 3, 7/8, and 9 are key innate immune sensors whose activities must be tightly regulated to prevent systemic autoimmune or autoinflammatory disease or virus-associated immunopathology. Here, we report a systematic scanning-alanine mutagenesis screen of all cytosolic and luminal residues of the TLR chaperone protein UNC93B1, which identified both negative and positive regulatory regions affecting TLR3, TLR7, and TLR9 responses. We subsequently identified two families harboring heterozygous coding mutations in UNC93B1, UNC93B1+/T93I and UNC93B1+/R336C, both in key negative regulatory regions identified in our screen. These patients presented with cutaneous tumid lupus and juvenile idiopathic arthritis plus neuroinflammatory disease, respectively. Disruption of UNC93B1-mediated regulation by these mutations led to enhanced TLR7/8 responses, and both variants resulted in systemic autoimmune or inflammatory disease when introduced into mice via genome editing. Altogether, our results implicate the UNC93B1-TLR7/8 axis in human monogenic autoimmune diseases and provide a functional resource to assess the impact of yet-to-be-reported UNC93B1 mutations.

Deletion of Interferon Lambda Receptor Elucidates Susceptibility to the Murine Model of Biliary Atresia.

Biliary atresia (BA) is a life-threatening cholangiopathy occurring in infancy, the most common indication for pediatric liver transplantation. The etiology of BA remains unknown; however, a viral etiology has been proposed as multiple viruses have been detected in explants of infants afflicted with BA. In the murine model of BA, Rhesus rotavirus (RRV) infection of newborn BALB/c pups results in a cholangiopathy that mirrors human BA. Infected BALB/c pups experience 100% symptomatology and mortality, while C57BL/6 mice are asymptomatic. Interferon-λ (IFN-λ) is an epithelial cytokine that provides protection against viral infection. We demonstrated that IFN-λ is highly expressed in C57BL/6, leading to reduced RRV replication. RRV-infection of C57BL/6 IFN-λ receptor knockout (C57BL/6 IFN-λR KO) pups resulted in 90% developing obstructive symptoms and 45% mortality with a higher viral titer in bile ducts and profound periportal inflammation compared to C57BL/6. Histology revealed complete biliary obstruction in symptomatic C57BL/6 IFN-λR KO pups, while C57BL/6 ducts were patent. These findings suggest that IFN-λ is critical in preventing RRV replication. Deficiency in IFN-λ permits RRV infection, which triggers the inflammatory cascade causing biliary obstruction. Further IFN-λ study is warranted as it may play an important role in infant susceptibility to BA.