Immunosuppression and infection in transplant recipients

Recognizing a foreign element is an inherent characteristic of living beings and guarantees their survival. Evading this defense mechanism is one of the most difficult requirements for transplant success, but it leads to a series of consequences, mainly related to infection. T lymphocytes are the cornerstone of the allogenic response. These cells recognize intracellular and extracellular antigens over HLA molecules in host cells. As a consequence, lymphocytic expansion occurring on several levels is produced, and a humoral or cellular response is the final result. The immunosuppression regimens used in transplantation include induction, maintenance and rescue therapy. Induction therapy serves primarily to decrease the proportion of T-cell precursors and to lower the efficacy of antigen presentation. With respect to maintenance therapy, cyclosporine and tacrolimus inhibit cytokine transcription, azathioprine, and mycophenolate mofetil inhibit nucleotide synthesis, and sirolimus and everolimus inhibit transduction of growth factor signals. As a consequence of immunosuppression, opportunistic microorganisms may appear with endogenic reactivation of latent infection or from an exogenous origin. Prevention of these infections by proper knowledge of the risk factors, rapid diagnosis, and adequate management are fundamental to guarantee the survival of the patient.