What mainly mediates acute rejection after transplantation?

Acute rejection after transplantation is primarily mediated by T cells, specifically CD4+ helper T cells and CD8+ cytotoxic T cells. This process occurs when the recipient's immune system recognizes the transplanted organ as foreign due to differences in human leukocyte antigens (HLA) between the donor and recipient. The activation of T cells leads to a cascade of immune responses that result in the infiltration of inflammatory cells into the transplanted tissue, causing damage and dysfunction.

T cell-mediated rejection involves two main phases: sensitization and effector responses. During the sensitization phase, dendritic cells present donor antigens to the T cells, leading to their activation and proliferation. In the effector phase, activated T cells directly attack the transplanted tissue, resulting in acute cellular rejection.

While B cells and antibodies can also play roles in rejection processes (such as in antibody-mediated rejection), it is the T cell-mediated immune response that predominantly governs the early stages of acute rejection post-transplantation. Understanding this mechanism is crucial for developing strategies to mitigate rejection and improve transplant outcomes.