STAT3 and graft versus host disease: The cytokine interleukin 6 (IL-6) plays a significant role in the initiation of the inflammatory response in different situations including tissue damage, infection, autoimmune disease as well as GvHD through activation of the signal transducer and activator of transcription 3 (STAT3) and mitogen activated protein (MAP) kinase pathways [5, 6].