A novel UNC93B1 gain-of-function mutation leads to TLR7 and TLR8 hyperactivation and systemic lupus erythematosus

Dysfunctions in nucleic acid-sensing Toll-like receptors (TLRs) disrupt nucleic acid tolerance, leading to systemic lupus erythematosus (SLE). Here, we report a novel homozygous gain-of-function p.R95L mutation in the TLR chaperone protein UNC93B1 in an SLE patient. Bulk and single-cell transcriptional analysis of the patient's peripheral blood mononuclear cells (PBMCs) revealed significantly elevated inflammation in T cells and myeloid cells due to enhanced dendritic cells function. The UNC93B1 R95L mutation leads to hyperactivation of TLR7/8, but not TLR3/9, upon stimulation with specific agonists in vitro. Transgenic Unc93b1R95L/R95L mice develop inflammatory and autoimmune phenotypes, and the upregulation of inflammatory signaling differs among organs, with a specific contribution of malfunctioned T cells and B cells. In human and mouse cell lines, the UNC93B1 R95L mutation promotes TLR7/8 signaling by enhancing its binding to ssRNA, without affecting TLR7/8 translocation. Overall, our results elucidate the pathology of organs and the immunological profiles of immune cell populations in the development of SLE caused by the UNC93B1 R95L mutation through the TLR7/8 axis.