Transplantation

Transplantation = transfer of tissue or organ ● autologous - donor = recipient ● syngeneic - genetically identical donor and recipient (identical twins) ● allogeneic - genetically nonidentical donor of the same species ● xenogenic - the donor of another species ● implant - artificial tissue compensation

Allotransplantation ● differences in donor-recipient MHC gp and secondary histocompatibility Ag ● alloreactivity of T lymphocytes - the risk of rejection and graft-versus-host disease ● direct detection of alloantigens – recipient T lymphocytes recognize the different MHC gp and non-MHC molecules on donor cells ● indirect recognition of alloantigens - APC absorb different MHC gp from donor cells and present the fragments to T lymphocytes ● CD8+ T cells recognize MHC gp I. ● CD4+ T cells recognize MHC gp II.

Recognition of alloantigens

Testing before transplantation ● ABO compatibility -risk of hyperacute or accelerated rejection (= formation of Ab against A or B Ag on graft vascular endothelium) ● HLA typing (determining of MHC gp alelic forms) phenotyping and genotyping by PCR ● Cross-match - lymphocytotoxic test – detection of preformed Ab (after blood transfusions, transplantation, repeated childbirth) ● Mixed lymphocyte reaction - testing of T lymphocytes alloreactivity, monitor for reactivity of lymphocytes to allogeneic HLA

HLA typing a) phenotyping: Evaluation of HLA molecules using typing serums Typing antiserums = alloantiserums of multipar (created cytotoxic Ab against paternal HLA Ag of their children), serum of patients after repeated blood transfusions, monoclonal Ab - molecules HLA class I: separated T lymphocytes - molecules HLA class II: separated B lymphocytes b) genotyping: evaluation of specific alleles DNA typing of HLA class II: DR, DP, DQ by PCR

Cross-match test ● determination of preformed antibodies ● recipient serum + donor lymphocytes + rabbit complement → if cytotoxic Ab against donor HLA Ag are present in recipient serum (called alloantibodies = Ab activating complement) → lysis of donor lymphocytes. Visualization of dye penetration into lysis cells. ● positive test = the presence of preformed Ab → risk of hyperacute rejection! → contraindication to transplantation

Mixed lymphocyte reaction (MRL) ● determination of T lymphocytes alloreactivity ● mixed donor and recipient lymphocytes → T lymphocytes after recognition of allogeneic MHC gp activate and proliferate One-way MRL ● determination of recipient T lymphocytes reactivity against donor cells ● donor cells treated with chemotherapy or irradiated lose the ability of proliferation

Mixed lymphocyte reaction (MRL)

Immunologically privileged sites and tissues Transplantation of some tissues don´t lead to the induction of allogeneic reactivity minimal content of lecocytes mechanisms that prevent to the development of injurious inflammation Evolutionarily significant, protection of vital organs (brain, eye, gonads) Factors protecting immunologically privileged structures isolation from the immune system preference of TH2 reactoin, supression of TH1 reaction FasL expression production of TGFb

Rejection Factors: ● The genetic difference between donor and recipient, especially in the genes coding for MHC gp (HLA) ● Type of tissue / organ - the strongest reactions against vascularized tissues containing many APC (skin) ● The activity of the recipient immune system - the immunodeficiency recipient has a smaller rejection reaction; immunosuppressive therapy after transplantation – suppression of rejection ● State of transplanted organ - the length of ischemia, the method of preservation, traumatization of organ at collection

Hyperacute rejection ● minutes to hours after transplantation ● humoral mediated immune response mechanism: ● if in recipients blood are present preformed or natural Ab (IgM anti-carbohydrate Ag) before transplantation → Ab + Ag of graft (MHC gp or endothelial Ag) → graft damage by activated complement (lysis of cells) ● the graft endothelium: activation of coagulation factors and platelets, formation thrombi, accumulation of neutrophil granulocytes prevention: ● negative cross match before transplantation, ABO compatibility

Accelerated rejection ● 3 to 5 days after transplantation ● caused by antibodies that don´t activate complement ● cytotoxic and inflammatory responses triggered by binding of antibodies to Fc-receptors on phagocytes and NK cells prevention: ● negative cross match before transplantation, ABO compatibility

Acute rejection ● days to weeks after the transplantation or after a lack of immunosuppressive treatment ● cell-mediated immune response mechanism: ● reaction of recipient TH1 and TC cells against Ag of graft tissue ● infiltration by lymphocytes, mononuclears, granulocytes around small vessels → destruction of tissue transplant

Chronic rejection ● from 2 months after transplantation ● the most common cause of graft failure mechanism is not fully understood: ● non-immunological factors (tissue ischemia) and TH2 responses with production alloantibodies, pathogenetic role of cytokines and growth factors (TGF β) ● fibrosis of the internal blood vessels of the transplanted tissue, endothelial damage →impaired perfusion of graft → gradual loss of its function dominating findings: vascular damage

Bone Marrow Transplantation ● Collection of hematopoietic stem cells ● Myeloablation ● Transplantation ● Engraftment ● Rejection ● Graft-versus-host reaction

Graft-versus-host (GvH) disease ● after bone marrow transplantation ● GvH also after blood transfusion to immunodeficiency recipients ● T-lymphocytes in the graft bone marrow recognize recipient tissue Ag as foreign (alooreactivity)

Acute GvH disease ● days to weeks after the transplantation of stem cells ● damage of liver, skin and intestinal mucosa ● prevention: appropriate donor selection, the removal of T lymphocytes from the graft and effective immunosuppression

Chonic GvH disease ● months to years after transplantation ● infiltration of tissues and organs by TH2 lymphocytes, production of alloantibodies and cytokines → fibrosis ● process like autoimmune disease: vasculitis, scleroderma, sicca-syndrome ● chronic inflammation of blood vessels, skin, internal organs and glands, which leads to fibrosis, blood circulation disorders and loss of function

Graft versus leukemia effect (GvL) ● donor T lymphocytes react against residual leukemick cells of recipient (setpoint response) ● mechanism is consistent with acute GvH ● associated with a certain degree of GvH (adverse reactions)

Immunologic relationship between mother and allogenic fetus

Immunologic relationship between mother and allogenic fetus ● fetal cells have on the surface alloantigens inherited from his father ● pregnancy = "semiallogenic transplantation“ Tolerance of fetus by mother allow the following mechanisms: ● the relative isolation of the fetus from maternal immune system (no mixing of blood circulation) ● trophoblast - immune barrier witch protects against mother alloreactive T lymphocytes - don´t express classical MHC gp, expresses non-classical HLA-E and HLA-G ● transfer of small doses of fetal antigens in maternal circulation causes tolerance ... suppressin of TH1 and preference of TH2 immune mechanisms in pregnancy

Rh incompatibility Complications in pregnancy: production of anti-RhD antibodies by RhD- mother carrying an RhD+ fetus (hemolytic disease of newborns) Fetal erythrocytes penetrate into the maternal bloodstream during pregnancy - a small amount, don´t immunize During childbirth or abortion (after 8 weeks of gestation) fetal erythrocytes can penetrate into the bloodstream of mother → immunization, formation of anti-RhD antibodies After childbirth, investigate Rh factor of born child, if is child Rh+, mother gets up to 72 hours after birth injection of anti-Rh antibodies (administered after abortion too)

Rh incompatibility

Anti-Rh(D) injection, this antibodies bind to RhD Ag on baby´s red blood cells, this Ag than can´t bind to BCR and can´t activate B lymphocytes, this immune comlexes also actively inhibit B lymphocytes During next childbirths, if fetus is Rh+ and mother produce anti-Rh antibodies, this Abb destroy red blood cells of fetus, which can lead to fetal death, or in severe postpartum anemia (anemia neonatorum) and neonatal jaundice (icterus gravis neonatorum) For each pregnant woman during the first trimester investigate blod Rh factor and the presence of antibodies, in Rh- women performed a test for antibodies also in II. and III. trimester

Immunopathological reactions

Classification by Coombs and Gell Immunopathological reactions: immune response, which caused damage to the body (secondary consequence of defense responses against pathogens, inappropriate responses to harmless antigens, autoimmunity) IV types of immunopathological reactions: Type I reaction - a response based on IgE antibodies Type II reaction - a response based on antibodies, IgG and IgM Type III reaction - a response based on the formation of immune complexes Type IV reaction - cell-mediated response

Immunopathological reactions based on antibodies IgG and IgM (reaction type II) Cytotoxic antibodies IgG and IgM: ● complement activation ● ADCC ● binding to Fc receptors on phagocytes and NK cells

Examples of immunopathological reaction Type II Transfusion reactions in administration of incompatibile blood: binding of antibodies to antigens on erythrocytes → activation of the classical way of complement → cell lysis Hemolytic disease of newborns: caused by antibodies against RhD antigen

Autoimmune diseases: ● organ-specific cytotoxic antibodies (antibodies against erythrocytes, neutrophils, thrombocytes, glomerular basement membrane ...) ● blocking or stimulating antibodies Graves - Basedow's disease - stimulating antibodies against the receptor for TSH Myasthenia gravis - blocking of acetylcholin receptor→ blocking of neuromuscular transmission Pernicious anemia - blocking the absorption of vitamin B12 Antiphospholipid syndrome - antibodies against fosfolipids Fertility disorder - antibodies against sperms or oocytes

Immunopathological reactions based on immune complexes formation (reaction type III) ● caused by IgG antibodies → bind to antigen → creation of immune complexes ● immunocomplexes - bind to Fc receptors on phagocytes - activate complement ● immune complexes, depending on the quantity and structure, are eliminated by phagocytes or stored in tissues ● pathological immunocomplexes response arises when is a large dose of antigen, or antigen in the body remains; arise 10-14 days after aplication of Ag and induced inflamation can get to chronic state ● immune complexes are deposited in the kidneys (glomerulonephritis), on the surface of endothelial cells (vasculitis) and in synovie joint (arthritis)

Serum sickness ● the therapeutic application of xenogeneic serum (antiserum to snake venom) ● creation of immune complexes and their storage in the vessel walls of different organs ● clinical manifestations: urticaria, arthralgia, myalgia Systemic lupus erythematosus ● antibodies against nuclear antigens, ANA, anti-dsDNA Farmer's lung ● IgG antibody against inhaled antigens (molds, hay) Post-streptococcal glomerulonephritis, cryoglobulinemia, revmatoid arthritis, post-infectious arthritis

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