1	CLSC320 Principles of Immunology Fundamental Concepts in Immunology Program for Clinical Laboratory Science Unit - 06 Immune Response To Tissue Antigens In Transplantation
2	Unit Guidelines Reading assignment: Pages 124 - 147 of textbook Learning objectives: Those listed on page125 of textbook Key terms: Those listed on pages 125 & 126 of textbook
3	General Features of Transplantation - 1 eTissue (allograft) transplanted between allogeneic (genetically non- identical) individuals will usually trigger an immune response. eThe immune response may be specific (cell-mediated or humoral) or nonspecific. eGraft rejection occurs when the class I and class II MHC molecules of the donor tissue do not Amatch@ those of the recipient. eThe severity of rejection may be limited in two ways: 1.by suppressing the recipient=s immune system 2.by testing for MHC compatibility (histocompatibility) prior to transplantation eTissue grafted between identical twins (syngeneic) does not result in rejection.
4	Major Histocompatibility Complex - 1 eIn humans this complex is called: human leukocyte antigen (HLA) eChromosome 6's short arm is where genes are located. eGenes code for a variety of proteins that are expressed on surfaces of a variety of cells. eThree classes of MHC gene products have been identified: Class I = Class II = Class III = HLA-A, HLA-B, HLA-C antigens HLA-D, HLA-DR, HLA-DQ, HLA-DP antigens properdin, C2, C4a, C4b, TNF", TNF(
5	MHC – I Facts Facts: Ufound on the surface of all nucleated cells Ualso found on the surface of platelets Uhighest concentrations found on: -T-cells -B-cells -Macrophages Uchains are composed of glycoproteins
6	MHC – I Drawing " chain $₂ microglobulin "₁ region "₂ region "₃ region transmembrane region peptide-binding grove extracellular domain intracellular domain
7	Function of MHC - I USpecific Tissue Markers: URecognition of Foreign Antigen: UGraft Rejection: -reflects the unique genetic makeup of individual -able to bind endogenous proteins on virally altered cells -serve as antigen-presenting cells -serve as target cells (due to virus inside) -CD8+ cells recognize antigen bound to MHC I -the principle antigen recognized by recipient=s immune system after tissue transplantation
8	MHC – II Facts Facts: Ufound on the surface of all immunocompetent cells: -Macrophages -Monocytes -B-cells -activated T-cells Ucells that do not normally express Class II MHC but can be induced to express it are: -resting T-cells -endothelial cells -thyroid cells Uchains are composed of glycoproteins
9	MHC – Class II Drawing " chain $ chain "₁ region "₂ region $₁ region $₂ region transmembrane region extracellular domain intracellular domain
10	Functions of MHC - II URecognition of Foreign Antigen: -able to bind processed antigen -serve as antigen-presenting cells -CD4+ cells recognize antigen bound to MHC II -initiation of immune response depends on: -CD4+ cell recognizes processed antigen as foreign
11	OSF – Graft vs Host Reaction On pages 130 - 131AOne Step Further@ presents a more in- depth discussion of the Graft - vs. - Host Reaction. This presentation is contained on a separate slide presentation called A One Step Further #9" The student may call up the slide program OSF-9 later or click on the arrow below to view slides now. Cytokines
12	MHC Antigens in Transplantation Transplantation of an Aallogeneic graft@ is the best understood and most practiced procedure in transplantation immunology. The genetic dissimilarity that exists between the donor MHC antigens and the recipient=s MHC antigens is the major reason for an immune reaction that causes graft rejection.
13	Types of Grafts Graph types: UAllogeneic graft (allograft): -Graft between two genetically different individuals of same species UAutologous graft (autograft): -Graft between two different body sites of same individual USyngeneic graft (syngraft): -Graft between two genetically identical individuals of same species UXenogeneic graft (xenograft): -Graft between two organisms of different species
14	Tissue Transplantation - Facts eLimiting factor: Uavailability of organs -forced safety procedures (seat belts, airbags, helmets, etc.) have resulted in decreased numbers of fatalities - hence organs. e1st successful kidney transplant: U1954 eMost common transplants: UCorneal USkin UBone marrow UKidney ULiver UHeart UPancreas 1835 in antelope 700 B.C. by Hindu surgeons 1987 1952 in Boston - syngraft - now >10,000/year 1963 - 1st one but 1980 before accepted 1967 - Dr. Barnard on Mr. Washkansky 1980 - before much success achieved
15	Pre-Transplant Testing ePretransfusion lab testing for renal transplants: UABO blood group testing -A and B antigens present on RBC=s and vascular endothelial cells UABO compatibility cross-match between donor & recepient. UHLA-A, -B,-C, -DR, and -DQ tissue typing -the closer the match the more successful the transplant UMixed leukocyte reaction -evaluates an in vitro immune response between donor mononuclear cells and recipient mononuclear cells to donor MHC antigens and recipient MHC antigens. -the greater the proliferation of cells the greater is the incompatibility of MHC antigens
16	Immunosuppression & Contrindications ePostransfusion immunosuppression: Ua variety of drugs are used to suppress the recipient=s immune system so rejection is minimized Ua more detailed discussion of immunosuppressive therapy will be presented later in this unit . eContraindication to transplantation: Uexistence of infection or disease (i.e. cancer)
17	Molecular Basis for Alloantigen Recognition URole of T-cell receptors (TCR=s) -TCR=s may recognize donor antigens in two ways: 1.host TCR=s recognize donor MHC molecules on graft tissue 2.host TCR=s recognize donor MHC-peptide complexes on graft tissue URole of T_Helper (CD4+) cells -CD4 cells recognize MHC class II molecules on donor tissue and produce cytokines as follows: 1.IL-2 & IFN-( activate T_Cytotoxic (CD8+) cells 2.IL-2, IL-4 & IL-5 activate B-cells 3.TNF-$ & IFN-( activate macrophages
18	Four Mechanisms of Graft Rejection UCell-Mediated cytotoxicity UAntibody-Dependent cytotoxicity - complement mediated UAntibody-Dependent cytotoxicity - cell mediated UNon-specific immune response - inflammation
19	Cell-Mediated Cytotoxicity -CD8 cells may become activate via two mechanisms: 1.Host CD4 cells recognize class II MHC- peptide complex on donor APC=s and secrete cytokines that activate B-cells, CD4, CD8, and macrophages which are all involved in the rejection reaction. 2.Host CD8 cells recognize class I MHC-antigen complex on donor graft cells and become activated and are capable of lysing graft tissue cells with the aid of CD4 cells (IL-2 & IFN-().
20	Antibody-Dependent Cytotoxicity Complement Mediated -host B-cells are activated by: ]IL-2, IL-4, & IL-5 from antigen activated T_Helper-cells -activated host B-cells then transform into plasma cells -plasma cells produce specific anti-graft antibodies -antibodies bind with HLA molecules of same specificity and complement is activated -complement then lyses endothelial cells of graft -C3a & C5a from complement activation act in inflammatory reaction
21	Antibody-Dependent Cytotoxicity Cell Mediated -host B-cells are activated by: ]IL-2, IL-4, & IL-5 from antigen activated T_Helper-cells -activated host B-cells then transform into plasma cells -plasma cells produce specific anti-graft antibodies -antibodies bind with HLA molecules of same specificity -Natural killer (NK) cells bind to Fc portion of antibody -graft tissue is lysed
22	Non-Specific Immune Response Inflammation -inflammation is a non-specific immune response in graft rejection that is mediated by: ]host T-cells ]inflammatory cells ]soluble mediators Review the AOne-Step-Further #1" for mechanisms involved in inflammation.
23	Cytokines & Graft Rejection IL-2 CYTOKINE CD4 & CD8 activate CD8 & B-cells IL-4 CD4, CD8, & mast B-cells switch to IgE IL-5 CD4, CD8, & mast activate eosinophils IFN-( CD4, CD8, & NK activate macrophages TNF-$ macrophages, T- cells, & NK activation of macrophages & lysis of cells SOURCE ACTION
24	Three Types of Graft Rejections UHyperacute graft rejection UAcute graft rejection UChronic graft rejection
25	Hyperacute Graft Rejection -Characteristics: ]rejection begins within minutes ]thrombosis within graft blood vessels -Mechanism: ]pre-existing antibodies bind to endothelial cells and activate complement causing thrombosis and necrosis ]pre-existing antibodies may be formed due to transfusions, pregnancy, or previous transplants
26	Acute Graft Rejection - 1 -Characteristics: ]two types of acute graft rejection: vvascular type vcellular type ]occurs within days or weeks of graft -Mechanism: ]vascular type: vIgG + C⁼ against endothelial cells vCD8 cells respond to Ab=s and : -lyse cells -cytokines induce inflammation
27	Acute Graft Rejection - 2 -Mechanism: - cont=d ]cellular type: vhost CD8 cells respond to presence of foreign antigen of donor graft vrelease cytokines that: -activate macrophages -activate other lymphocytes vresults in high numbers of lymphocytes and macrophages found in parenchymal cells of graft
28	Chronic Graft Rejection -Characteristics: ]slow process that takes months or even years ]fibrosis occurs ]results in loss of normal organ structure & function -Mechanism: ]slow cell-mediated rejection ]caused by antibody-antigen complexes being deposited in donor tissue
29	Immunosuppressive Drugs - Steroids 1.Steroids: -prednisone: -methylprednisone ]suppress inflammatory and immune reactions by: valteration of leukocyte circulation Nincreased neutrophils Ndecreased lymphocytes vimpair macrophage activity Ndecreased presentation of antigen vreduction in monocyte production Ndecreased macrophages
30	Immunosuppressive Drugs - Cytotoxic 2.Cytotoxic drugs: -cyclophosphamide: -azathioprine drug of choice -methotrexate -chlorambucil ]suppress proliferation of cells 3.Cyclosprine drugs: -cyclosporine A ]most important immunosuppressive drug used ]selectively impairs CD4 cells production of IL-2 ]thus suppresses CD8 cell production ]is not cytotoxic
31	Other Methods of Immunosuppression 1.Anti-lymphocyte antibodies (polyclonal): -non-specific against T- lymphocytes -impairs cell-mediated immune responses -complications that arise: ]lack of standardization of dose ]cross-reactivity with host tissues ]inducing antibody production of host against these antibodies 2.Anti-lymphocyte antibodies (monoclonal): -specific against T- lymphocytes -shows no cross-reactivity with host tissues
32	Tissue Transplantation Press the ESC key to end program
33	One Step Further Graft-vs-Host Reaction OSF - 9 Pages 130 & 131 7click button to return to main program
34	Graft-vs-Host Reaction - 2 Initiation of Host-vs-Graft Reactions: Initiation of Graft-vs-Host Reactions: ein allografts (grafts between same species) that differ from a recipient at the class I and class II MHC loci (resulting in dissimilar antigenic molecules), both the CD8+ and CD4+ cells of the host become activated and the resulting immune response is against the grafted tissue of donor ein allografts (grafts between same species) that differ from a recipient at the class I and class II MHC loci (resulting in dissimilar antigenic molecules), both the CD8+ and CD4+ donor cells become activated and the resulting immune response is against the tissues of the host (recipient)
35	Graft-vs-Host Reaction - 3 Conditions that may cause a Graft-vs-Host Reaction: ethere are differences in tissue histocomaptibility between donor and host ethe host is immunocompromised ethe graft cells are immunocompetent and are able to trigger an immune reaction against host tissue eprocedures or products that may cause GVD when immunocompetent lymphocytes are present include: Žintrauterine transfusions Žblood transfusions - whole, packed, or frozen Žplatelet transfusions Žplasma transfusions - fresh or frozen Žtransplantation of fetal thymus Žtransplantation of fetal liver Žtransplantation of bone marrow
36	Graft-vs-Host Reaction - 4 Graft-vs-Host Reaction (GVD) and Graft-vs-Host Disease (GVHD): ewhen the Graft-vs-Host reaction injures the host tissues such that loss of function occurs in the affected area, it is then called Graft-vs-Host Disease (GVHD). Classification of Graft-vs-Host Disease (GVHD): ebased on the histiologic pattern observed at site of tissue injury Žacute GVHD: wepithelial cells necrosis in: -skin, liver, and GI tract wrash, jaundice, diarrhea, and pulmonary infiltrates wdeath may result from increased susceptibility to infections
37	Graft-vs-Host Reaction - 5 Classification of Graft-vs-Host Disease (GVHD): continued Žchronic GVHD: wpresence of fibrosis and atrophy of one of the target sites: -skin, liver, and GI tract wdysfunction of target site may lead to death woccurs in patients that have severe immunodeficiency woccurs in immunodeficient patients that have received transfusions containing immunocompetent lymphocytes within 5 - 30 days wsecondary infections are frequently seen in patients with GVHD
38	Graft-vs-Host Reaction - 6 Mechanism: enot well understood eNatural killer cells (NK) act as effector cells ebelief is that IL-2 activates NK cells to become lymphokine-activated killer cells (LAK) eNK cells are seen attached to dying epithelial cells eLAK cells are not MHC-restricted and are able to lyse host cells
39	Graft-vs-Host Reaction - 7 Treatment: etreated using immunosuppressive therapy in patients with GVH eimmunosuppressive therapy of little help in patients with GVHD ecyclosporine may help in patients with GVHD Prevention: ePatients who are immunocomromised should: Žbe typed for HLA antigens Žtested for compatibility with blood products Žreceive blood products that have been irradiated to destroy viable lymphocytes
40	Graft-vs-Host Reaction - 7 7click button to return to main program