This is a humanized IgG4 antibody using the same sequences as the therapeutic antibody mirikizumab. It is designed to bind to the p19 subunit of interleukin 23 for the treatment of immune-mediated diseases, including ulcerative colitis, Crohn’s disease and psoriasis. IL23, a member of the IL12 family of cytokines, has 2 components: the p40 subunit, which is shared by IL12, and the p19 subunit, which is found in IL23 but not IL12. Both IL23 and IL12 can activate the transcription activator STAT4, and stimulate the production of interferon-gamma (IFNG). In contrast to IL12, which acts mainly on naive CD4(+) T cells, IL23 preferentially acts on memory CD4(+) T cells. IL23 also plays a key role in the maintenance and amplification of T helper 17 (Th17) cells and the stimulation of many innate immune cells, which are important in the pathogenesis of chronic inflammatory diseases, including UC.