SIGIRR (single immunoglobulin and TIR domain containing) functions as a crucial negative regulator of innate immune signaling pathways, particularly those mediated by Toll-like receptors (TLRs) and interleukin-1 receptors (IL-1Rs) 1. The protein attenuates TLR4 signaling through TIR-TIR domain interactions and interferes with IL-1R1/IL1RAP heterodimerization via its extracellular domain 2. SIGIRR expression is constitutively present in various cell types but becomes downregulated during inflammatory conditions, such as LPS stimulation in bladder epithelial cells and severe acute pancreatitis 23. Mechanistically, SIGIRR knockdown leads to enhanced NF-κB and MAPK activation, increased cytokine production, and reduced LPS tolerance 2. The protein plays protective roles in multiple disease contexts: it preserves intestinal barrier integrity during severe acute pancreatitis by inhibiting TLR4 signaling 3, and its dysregulation is associated with rheumatoid arthritis susceptibility 4. Additionally, SIGIRR serves as a checkpoint regulator in NK cells, with its blockade enhancing NK cell-mediated anti-tumor and anti-viral responses 5. These findings establish SIGIRR as a critical immune checkpoint molecule with therapeutic potential in inflammatory and autoimmune diseases 6.