Interleukin-6: An Important Mediator of Allograft Injury.

Interleukin-6 (IL-6) is a cytokine with critical innate and adaptive immunity functions. Its diverse immunological and physiological actions include direction of immune cell differentiation, initial response to invading pathogens and ischemic injury, sustained plasma cell growth, and immunoglobulin production. IL-6 transcriptional dysregulation is commonly seen in patients with autoimmune or inflammatory disorders. Emerging information suggests that IL-6 transcription is upregulated in patients with kidney and heart transplant rejection and may account for perpetuation of inflammatory responses in the allograft, leading to allograft rejection and vasculopathy. IL-6-directed therapeutics include monoclonal antibodies directed at IL-6, the IL-6 receptor (IL-6R), and Janus kinase inhibitors. IL-6-mediated signaling to cell targets is unique, involving classic signaling (IL-6->IL-6R) cell membrane receptors, transsignaling (IL-6->soluble IL-6R->gp130) which activates any cell, and the recently discovered IL-6/IL-6R transpresentation in which antigen-presenting cells synthesize and express IL-6/IL-6R complexes, which are transported through the cell membrane subsequently interacting with gp130 to costimulate T cells. Currently, there are new trials in autoimmunity and heart and kidney transplantation to determine effectiveness of inhibiting IL-6/IL-6R to ameliorate chronic allograft rejection and coronary allograft vasculopathy. Therapeutic trials aimed at prevention of ischemia/reperfusion injury to allografts based on animal data should be considered.