MyD88, also known as myeloid differentiation primary response gene 88, is a protein encoded by the MyD88 gene. It belongs to the Toll/IL-1R family and the death domain family, and is essentially a cytosolic soluble protein. The structure of MyD88 protein includes an N-terminal death domain (DD), a middle structural domain, and a C-terminal Toll/interleukin-1 receptor (TIR) domain. The DD region can interact with other proteins possessing DD to form homodimers or heterodimers, which further induce the activation of c-Jun N-terminal kinase (JNK) or nuclear factor-κB (NF-κB). It is also associated with TLR-mediated apoptosis. On the other hand, the TIR domain can bind to other TIR domains, mediating signal transduction. MyD88 plays a crucial role in the immune system, serving as a key adaptor molecule in the Toll-like receptor (TLR) signaling pathway. Primarily located in the cytoplasm, it functions as a pure adapter connecting IL-1R1 to downstream IRAK kinases. By recognizing pathogens, MyD88 induces the production of proinflammatory cytokines and upregulation of costimulatory molecules, triggering rapid activation of the innate immune response. Additionally, MyD88 is involved in regulating genes related to immunity, inflammation, and cell survival.