TLR7 gain-of-function genetic variation causes human lupus

While circumstantial evidence supports enhanced TLR7 signaling as a mechanism of human systemic autoimmune disease, we have lacked the proof afforded by lupus-causing TLR7 gene variants. Here we describe human systemic lupus erythematosus (SLE) caused by TLR7 gain-of-function (GoF). We identified a de novo, novel, missense TLR7 Y264H variant in a child with severe lupus. The de novo TLR7 Y264H variant selectively increased sensing of guanosine and was sufficient to cause lupus when introduced in mice (kika mice). We performed RNA-seq of kika and wild type B cells cultured for 20 hours with anti-IgM and found a decreased tendency to apoptosis in kika B cells, including decreased expression of active Caspase 3 and also a small decrease in proliferation. Overall, these results suggest that hypersensitive TLR7 signaling allows the survival of B cells that are binding self-antigen through their surface BCR. Spleens were obtained from wild type or Tlr7Y264H mice (kika mice). Total B cells were purified and then stimulated with anti-mouse IgM (10 µg/mL) for 20 hours.