![]() A negative cross-match against T cells but a positive cross-match against B cells indicates a higher risk of acute rejection, but transplantation may still be performed with a high level of caution.A negative cross-match against T and B cells indicates a lower risk of rejection reactions therefore, transplantation may be performed.Recipient serum is examined for preformed antibodies ( donor-specific antibodies) against donor T and B lymphocytes.Prerequisites for organ matching Cross-matching (transplantation) The activated helper T cells help the plasma cells produce alloantibodies → damage the target cell directly or induce antibody-dependent cell-mediated cytotoxicity. ![]() The activated helper T cells recruit recipient macrophages to the graft.Activated helper ( CD 4) T cells recognize HLA class II molecules on dendritic cells within the transplanted organ.Activated cytotoxic ( CD 8) T cells recognize other HLA class I molecules on all cells in the donor graft and cause target cell death by releasing molecules such as perforin and granulozyme.Clinical importance: Activation of a particular T cell by a foreign HLA peptide results in clonal proliferation of that type of T lymphocyte, a process that is mediated by IL-2 and leads to acute rejection.Direct allorecognition: HLA molecules on the allograft are exceptionally strong antigens and can directly stimulate the T cells without being broken down and presented by the antigen-presenting cells of the recipient.The antigens are then broken down and presented by the antigen-presenting cells.HLA molecules on an allograft are extremely different from those of the recipient and are thus treated as foreign antigens by the antigen-presenting cells of the recipient.Definition: recognition of a foreign antigen as a non-self antigen by a host.See “ Major histocompatibility complex” for more details. The HLA II cluster codes for class II MHC m olecules and also consists of three loci: HLA-DR, HLA-DP, and HLA-DQ.The HLA I cluster codes for class I MHC molecules and consists of three loci: HLA-A, HLA-B, and HLA-C.MHC: proteins present on the surface of all cells that display antigenic peptide s as a normal physiological function so that they can be recognized by T lymphocytes as either self or non-self antigens.HLA: a gene cluster on chromosome 6 that codes for MHC molecules.Transplant immunology Major histocompatibility complex ( MHC) and human leukocyte antigen ( HLA)
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