TGFB1 and rheumatoid arthritis: In addition to IL-6, TGF-β1, and IL-23, the expression of IL-17A is regulated by retinoids, in particular RA (Figure 2), which is important in the context of liver disease and fibrosis, since the liver is the main site of storage of Vitamin A. RA is capable of inhibiting the expression of RORγτ, promoting the development of iTregs and the expression of FoxP3.