NBME Exam 2023 WITH 100% CORRECT ANSWERS

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Graft-versus-host disease (GVHD) Follows bone marrow transplantation. -Transplanted donor mature T cells that recognize self-tissue as foreign -new T-cells will be educated in the recipient's thymus -must be some histoincompatibility -the recipient must be immunocompromised -type IV hypersensitivity reaction Autograft From one part of the body to another Isograft transplant between genetically identical individuals (usually twins) Allograft organ transplant between members of the same species Xenograft organ transplant between members of different species What leads to transplant rejection? T-cells from either the recipient or the donor bone marrow recognizes the other person's different HLAs (i.e. alloantigens) and attack the transplant or recipient. Alloantigens molecules that differ in the same species (ex: HLA mismatches) that are recognized by the lymphocytes of the recipient in organ donation 3 ways to be exposed to HLA proteins Transfusion, pregnancy, transplant Direct pathway of allorecognition a donor APC (with foreign MHC) interacts with recipient CD4+ and CD8+ T cells, CD4+ T-cells interact with B-cells which go on to produce antibodies specific to the donor tissue -leads to ACUTE rejection via humoral and cell-mediated response Indirect pathway of allorecognition Recipient APC ingests, processes, and presents donor peptide to T-cells. Subsequent graft rejection is mainly due to CD4+ T-cells that secrete inflammatory cytokines that injure the graft. -CHRONIC rejection Semi-direct pathway of allorecognition Recipient APC takes donor tissue in through exosome and presents foreign/donor MHC as well as self/recipient-MCH -T-cell response leads to graft rejection Mixed Lymphocyte Reaction (MLR) In vitro model of T-cell recognition of alloantigens to assess donor match. -T-cells from one person are cultured with leukocytes from another person and the responses are assayed. The magnitude of this response is proportional to the extent of the MHC differences between those two individuals and is a rough predictor of the outcomes of grafts exchanged between these individuals.

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