A shedding soluble form of interleukin-17 receptor D exacerbates collagen-induced arthritis through facilitating TNF-α-dependent receptor clustering

Rheumatoid arthritis (RA) is exacerbated by TNF-alpha signaling. However, it remains unclear whether TNF-α-activated TNFR1 and TNFR2 are regulated by extracellular factors. Here, we showed that soluble glycosylated interleukin-17 receptor D (sIL-17RD), which was produced by proteolytic cleavage, enhanced TNF-α-induced RA. We revealed that IL-17RD shedding was induced by the proteolytic enzyme TACE and enhanced by TNF-α expression in macrophages. Intriguingly, sIL-17RD was elevated in the sera of arthritic mice and rats. Recombinant sIL-17RD significantly enhanced the TNF-α-induced proinflammatory response by promoting TNF-α-TNFR–sIL-17RD complex formation and receptor clustering, leading to the accelerated development of collagen-induced arthritis. Our observations revealed that ectodomain shedding of IL-17RD occurred in RA to boost the TNF-α-induced inflammatory response. Targeting sIL-17RD may provide a new strategy for the therapy of RA.