TIR8/SIGIRR: an IL-1R/TLR family member with regulatory functions in inflammation and T cell polarization

TIR8, also known as single Ig IL-1 receptor (IL-R)-related molecule, SIGIRR, is a member of the IL-1R like (ILR) family. Unlike most other members of this family, it has a single extracellular Ig domain, a long cytoplasmic tail and a Toll/IL-1R (TIR) domain with two amino acid substitutions possibly consistent with non-conventional signaling. The TIR8 structure and pattern of expression are conserved in evolution from birds to humans. Current evidence suggests that TIR8 inhibits signaling receptor complexes of IL-1 family members associated with Th1 (IL-18), Th2 (IL-33) and Th17 (IL-1) differentiation. TIR8 also dampens TLR-mediated activation. The ability to dampen signaling from ILR family members and TLRs makes TIR8 a key regulator of inflammation, cancer-related inflammation, and autoimmunity.