TLRs signaling overview. This figure depicts the endogenous ligands released during xenotransplantation that trigger two of the most important TLR receptors, TLR2 and TLR4, and the MyD88-dependent and MyD88-independent (TRIF-dependent) signaling pathways activated by TLRs. Abbreviation: TLR, toll-like receptor; MyD88, myeloid differentiation primary response protein 88; Mal, MyD88-adapter like; TIRAP, TIR domain-containing adapter; TRAK, TSH-receptor antibody test; TRAM, Trif-related adaptor molecule; TRIF, TIR domain-containing adaptor protein inducing type 1 interferons; TBK1, TANK binding Kinase-1; IRF, interferon regulatory factor; MAPK, mitogen-activated protein kinases; JNK, c-Jun N-terminal kinase; ERK, extracellular signal-regulated kinase; RIP1, Receptor-Interacting Protein 1; TRAF6, tumor necrosis factor-receptor-associated factor-6; TAK1, TGF-β-activated kinase-1; TAB1, TAK1-Binding Protein-1; TAB2, TAK1-Binding Protein-2; UBC13, ubiquitin-conjugating enzyme-13; UEV1A, ubiquitin-conjugating enzyme E2-variant-1; IKK, IkappaB kinase; AP-1, transcription factor complex-1; interleukin, IL; IFN, interferon; TNF, tumor necrosis factor.