Adapter protein involved in the Toll-like receptor and IL-1 receptor signaling pathway in the innate immune response. Acts via IRAK1, IRAK2, IRF7 and TRAF6, leading to NF-kappa-B activation, cytokine secretion and the inflammatory response. Increases IL-8 transcription. Involved in IL-18-mediated signaling pathway. Activates IRF1 resulting in its rapid migration into the nucleus to mediate an efficient induction of IFN-beta, NOS2/INOS, and IL12A genes. Upon TLR8 activation by GU-rich single-stranded RNA (GU-rich RNA) derived from viruses, induces IL1B release through NLRP3 inflammasome activation (By similarity). MyD88-mediated signaling in intestinal epithelial cells is crucial for maintenance of gut homeostasis and controls the expression of the antimicrobial lectin REG3G in the small intestine (By similarity). Homodimer. Also forms heterodimers with TIRAP. Binds to TLR2, TLR4, TLR5, IRAK1, IRAK2 and IRAK4 via their respective TIR domains. Interacts with IL18R1. Interacts with BMX, IL1RL1, IKBKE and IRF7. Interacts with LRRFIP1 and LRRFIP2; this interaction positively regulates Toll-like receptor (TLR) signaling in response to agonist. Interacts with FLII. LRRFIP1 and LRRFIP2 compete with FLII for MYD88-binding. Interacts with IRF1. Upon IL1B treatment, forms a complex with PELI1, IRAK1, IRAK4 and TRAF6; this complex recruits MAP3K7/TAK1, TAB1 and TAB2 to mediate NF-kappa-B activation. Direct binding of SMAD6 to PELI1 prevents the complex formation and hence negatively regulates IL1R-TLR signaling and eventually NF-kappa-B-mediated gene expression. May interact with PIK3AP1. Interacts (via TIR domain) with DHX9 (via H2A and OB-fold regions); this interaction is direct. The intermediate domain (ID) is required for the phosphorylation and activation of IRAK.