Acts as a negative regulator of the Toll-like and IL-1R receptor signaling pathways. Attenuates the recruitment of receptor-proximal signaling components to the TLR4 receptor, probably through an TIR-TIR domain interaction with TLR4. Through its extracellular domain interferes with the heterodimerization of Il1R1 and IL1RAP (By similarity). Interacts with IL1R1, IRAK1, TLR4, TLR5, TLR9 and TRAF6. Upon IL-1 stimulation found in a complex at least composed of IL1R1, SIGIRR, MYD88, IRAK1 and TRAF6. Upon stimulation with LPC found in a complex at least composed of TLR4, SIG1IR, MYD88, IRAK1 and TRAF6. Interacts with PALM3 (By similarity). Belongs to the interleukin-1 receptor family.