TLR7 and rheumatoid arthritis: Furthermore, a large number of studies have shown that along the signaling pathway from the upstream receptor (TLR7/8/9), to the intermediate adapter (SLC15A4/TASL) and the downstream transcription factor (IRF5), the abnormal function of any of those components may lead to autoimmune diseases, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA)23–31.