IL37 and ulcerative colitis: Interleukin-23 (IL-23) consists of 2 subunits: p40, shared with interleukin-12 (IL-12), and the unique p19 subunit.1 Mirikizumab, a humanized IgG4-variant monoclonal antibody that binds to p19, has shown efficacy in treating ulcerative colitis (UC).2 However, patients previously treated with ustekinumab, a monoclonal antibody targeting p40, were excluded from phase 3 trials of mirikizumab, resulting in a lack of clinical evidence for such cases.