Inflammatory bowel disease (IBD) is a group of immune-mediated diseases that are treated with immunosuppressants such as Janus kinase 1 inhibitors (JAK1i). The relevant side effects of immunosuppressants include infections. Herpes viruses (including the varicella zoster virus - VZV) remain in the body for life and can reactivate in the event of immunodeficiency. Under treatment with JAK1i, there is an increased risk of VZV reactivation in individuals with IBD. Natural killer (NK) cells are part of the immune system and are important for controlling viral infections. The aim of this project is to investigate the influence of JAK1i on the antiviral function of NK cells and the control of different herpes virus infections in order to better prevent these complications.