Interleukin-6 (IL-6), a pleiotropic pro-inflammatory cytokine. In the context of transplant rejection, IL-6 plays a central and multifaceted role in promoting both adaptive and innate immune responses that damage the graft. It drives the differentiation and activity of antibody-producing plasma cells and memory B cells, which generate donor-specific antibodies (DSAs) that attack the transplant. Simultaneously, IL-6 promotes T-cell activation and inhibits the development of regulatory T cells (Tregs).