Figure 1.

The JAK-STAT signalling pathway. Many cytokines important in the pathogenesis of inflammatory bowel disease [IBD] signal via the JAK-STAT pathway. Cytokine signalling induces phosphorylation of JAKs, which phosphorylate STAT proteins. STAT proteins form homo- or heterodimers and migrate into the nucleus where they activate transcription of inflammatory cytokines. JAK inhibitors are new therapeutic agents currently being investigated in clinical trials in IBD. First-generation JAK inhibitors [e.g. tofacitinib] target multiple JAKs, whereas second-generation JAK inhibitors [e.g. filgotinib] selectively target one JAK.