IL23A and psoriasis: Ustekinumab was approved by the FDA for the treatment of psoriasis in 2009 and is currently the only IL-12/IL-23p40 inhibitor for this disease.466 It is a monoclonal antibody that specifically binds to the shared p40 subunit of IL-12 and IL-23, blocking the signaling pathways that are activated by normal ligand-receptor binding.