TLR9 and systemic lupus erythematosus: Tretinoin is a potent inhibitor of Pin1, effectively blocking the TLR-7/TLR-9/Pin1/IRAK-1/IRF-7 signaling pathway by inhibiting and degrading activated Pin1, making it an attractive candidate for treating SLE, as Pin1 plays a key role in preventing the progression of the disease (63).