PDE4A and rheumatoid arthritis: Moreover, the phosphodiesterase 4 (PDE4) inhibitor Apremilast (Otezla®) strongly inhibited IL-12/IL-23p40 in cultured synovial fluid mononuclear cells from patients with active RA, psoriatic arthritis or peripheral spondyloarthritis (Kragstrup et al., 2019[98]).