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Immunology: Week 8 (Transplants: transfer of cells, tissues, or organs…
Immunology: Week 8
Transplants: transfer of cells, tissues, or organs from a donor to a recipient
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Graft Types
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REJECTION due to specificity and memory (Think of second exposures in adaptive immunity)
First-set Rejection (10-14 days): tissue is grafted, revascularization occurs, inflammation (cellular infiltration) causes damage to cells and the graft dies (thrombosis and necrosis)
Second-set Rejection (5-6 days): No revascularization - reaction occurs much more quickly than in first-set rejection
TYPES
Hyperacute (≥ 24 hr): occurs from preexisting Igs and before revascularization. Igs bind to graft cells and activate the complement system.
Acute (7-10 days): mediated by T-cell responses, massive infiltration and macrophages indicate Th-cell activation and proliferation, and rejection occurs mostly through effector stage mechanisms # #
Chronic (Months-Years): develops after acute rejection reactions have stopped, thought to be due to co-responses between humoral and cell mediators #
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Allografts are most likely to last the longest, but chronic rejection is more common with each passing year after tranplantation (wrt kidney transplants)
STAGES
Sensitization Stage: CD4+, CD8+ and T cells recognize alloantigens expressed on foreign graft cells
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Donor MHC peptides may or may not be recognized in recipient's APC MHC through indirect presentation
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Acceptance (12-14 days): tissue is grafted, revascularization occurs, the foreign and resident tissue heal and reach resolution
Allograft Tolerance (what we tissues we naturally tolerate) #
Tissues at sequestered sites in body, have no lymphatic vessels (eyes, brain, testes, uterus)
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Tissues w/o alloantigens (cartilage, heart valves) #
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