Inflammatory and Immune Pathways in Kidney Transplant Rejection: Current Evidence and Future Perspectives

Kidney transplantation remains the optimal treatment for end-stage renal disease, yet long-term allograft survival has plateaued due to persistent rejection. This review provides a comprehensive overview of the inflammatory and immune pathways implicated in kidney allograft rejection, integrating current evidence from basic and translational research. Ischemia–reperfusion injury initiates an inflammatory cascade through the release of damage-associated molecular patterns, activating Toll-like receptors and the complement system, thereby priming the alloimmune response. Innate immune cells, including macrophages, dendritic cells, and natural killer cells, bridge sterile tissue injury to adaptive alloimmunity, while the emerging concept of trained immunity reveals long-lasting epigenetic reprogramming of monocytes with direct implications for graft longevity. The adaptive response encompasses T cell-mediated rejection, driven by Th1, Th17, and CD8+ cytotoxic lymphocytes, and antibody-mediated rejection, mediated by donor-specific antibodies through complement activation and antibody-dependent cellular cytotoxicity. Key signalling pathways, including JAK-STAT, NF-κB, NLRP3 inflammasome, and mTOR, amplify allograft inflammation and promote progression toward chronic injury. Macrophage polarisation and macrophage-to-myofibroblast transition have been identified as major drivers of interstitial fibrosis and late graft failure. Recent advances in non-invasive biomarkers, such as donor-derived cell-free DNA and molecular phenotyping, are transforming rejection diagnostics. Emerging therapies, including costimulation blockade, anti-CD38 antibodies, complement inhibitors, and regulatory T cell-based approaches, offer the potential to shift transplant medicine toward precision-guided, tolerance-inducing strategies. This review synthesises these developments and discusses future perspectives for improving long-term allograft outcomes.