HLA antigens (Human Leukocyte Antigens) = human MHC (Main Histocompatibility Complex) antigens Downloaded from: StudentConsult (on 4 August 2013 10:57 AM) © 2005 Elsevier Polymorphism of human MHC antigens 2010 Numbers of HLA Alleles HLA Class I Alleles 3,411 HLA Class II Alleles 1,222 HLAAlleles 4,633 Other non-HLAAlleles 110 Polymorphism of human MHC antigens HLA genes are localized on 6p chromosome Co-dominant expression of HLA genes HLA-I antigens HLA-II antigens Downloaded from: StudentConsult (on 18 July 2006 08:13 AM) © 2005 Elsevier Binding of antigenic peptide to HLA molecule Jan Klein, Ph.D., and Akie Sato, Ph.D.: The HLA System. N Engl J Med 2000; 343:702- 709 Downloaded from: StudentConsult (on 18 July 2006 08:13 AM) © 2005 Elsevier Interaction of TCR with HLA+antigen Superantigens • Bind to invariant regions of HLA-II and TCR. • The consequence is a polyclonal stimulation of lymphocytes without presence of antigen. • This stimulation may lead to autoimmune reaction. • High quantity of released cytokines may lead to a severe damage of the organism. • Examples: staphylococcal enterotoxin, erytrogenic toxin of Streptococcus toxin streptokoků Activation of TCR by antigen and superantigen MHC class II Signal transduction Superantigen T cell APC TRC Signal transduction αβ α β αβ α β Antigen Initiation of the immune response, Role of HLA antigens Two types of antigens as regards antibody production stimulation • T- dependent. Initiation of immune response requires antigen presenting cells, T-lymphocytes. Includes majority of antigens. • T-independent. For the stimulation of B-cells Tlymphocytes (and APC) are not necessary. Polysacharides are typical examples. Only IgM is produced (not other isotypes). No immune memory is induced. • T Role of HLA antigens in immune response • HLA-I: Expressed on all nucleated cells. Presentation of endogenous antigens to CD8+ cells. This leads to activation of the CD8+ cell and cytotoxic effect on antigen-presenting cell. • HLA-II Expressed on professional antigenpresenting cells – monocytes, macrophages, dendritic cells, B-cells. Presentation of exogenous antigens to CD4+ cells. This leads to activation of the CD4+ (and also the antigen presenting cell). Downloaded from: StudentConsult (on 18 July 2006 08:13 AM) © 2005 Elsevier Role of HLA antigens in immune response Degradation and presentation of antigens on HLA-II molecules Presentation of endogenous antigens by HLA-I Proteasome cleaves protein into short paptides Cytosolic antigen TAP MHC class I glycoprotein Nucleus Golgi apparatus T cell T-cell receptor CD 8 Endoplasmic reticulum T-cell stimulation by antigen is a complex reaction PAMP Quiescent T-cell pathogen antigen Toll-like receptor Antigen-presenting cell MHC class II molecule peptide T-cell receptor B 7 CD 28 activation Downloaded from: StudentConsult (on 20 July 2006 09:34 AM) © 2005 Elsevier Surface structures of T-lymphocytes Costimulatory signals in T-cell activation Function of Th1 cells Initiation of antibody response in T-cell dependent antigens Activation of immune system by antigen B-cell receptor Antigen Antibodies Interleukin 4,5,6 B-cell activation Interleukin 4 Antigen presenting cell B cell peptide DC80/86 MHCII CD28 Th0 T Cell Th2 T Cell Interleukin 4 Expression of viral antigens on HLA-I molecules HLA antigens and diseases • Various, predominantly immunopathologic, diseases are more frequent in persons with some HLA antigens. • Presence of the HLA antigen makes a predisposition for development of the disease (increased relative risk), but not cause a disease. • Majority of the carriers of the „disease associated antigen“ are healthy! Ankylosing spondylitis • Males predominantly affected, frequency 1:1000. • Usually starts with sacroileitis, consequently vertebral column is affected. • Fibrotisation and ossification of intervertebral joins and filaments. • The process leads to decreased mobility and ankylosis in terminal state. • Ninety-five percent of patients are HLA-27 positive. Ankylosing spondylitis Ankylozing spondylitis and HLA B-27 • Frequency of the disease is 1:1000. • Ninety-five percent of patients are HLA-27 positive (in Caucasian population). • But: HLA-27 is present in approximately 5% of people only 1 / 50 HLA B-27+ persons will develop ankylosing spondylitis! • Negativity of HLA-B27 almost excludes the diagnosis of ankylosing spondylitis. • Pozitivity – only shows that the patient has the predisposition! It does not make a diagnosis! Coeliac disease • Haplotype HLA-DQ2 / HLA-DQ8 is expressed in majority of patients with coeliac disease. • However these HLA genes are present in approximately 40% of general population. Only in 3-4% of them will develop the celiac disease. • The test for HLA DQ2/DQ8 has high negative predictive value (can exclude the disease) but minimal positive predictive value (cannot make a diagnosis). Regulation of the immune response – Interactions of the components of the immune system – Characteristcs of the stimulating antigen (PAMPs, T-dependent and T-independent antigens) – Neuroendocrine interactions Regulation inside the immune system – Physical interactions among cells – through surface molecules transmitting positive or negative signals. – Chemical signals – cytokines, regulation by antibodies (idiotype-antiidiotype interactions) Costimulatory molecules involved in the interaction between APC and T-lymphocyte APC T-lymphocyte Regulation by T-lymphocytes • Relation between Th1 and Th2 cells • Various types of regulatory cells Development and function of Th1 and Th2 cells Bacteria TH 1 TH 0 TH 2 Macrophage NK cell Mast cell Treg lymphocytes • Separate subgroup of regulatory T-cells • Thymic development, although the development in periphery was also documented (i-Treg). • CD4+CD25+ • Suppress immune reaction against self-antigens • 5-10% of peripheral CD4+ cells • Mechanisms of regulation: Production of TGF b, expression of CTLA-4 …. TR-1 lymphocytes • Induced i periphery by antigen. • CD4+ • Production of high levels of IL-10, IFN-g, TGF-b, but not IL-2. • Similar function have Th3 cells T-lymphocyte checkpoints • Stimulatory – CD27 (ligand CD70 - APC), – CD28 (Ligand CD80, 86 - APC), – CD40 – expressed on APC, B-ly (ligand CD154 = CD40L – T-ly) , – OX40 – activates and memory T-ly (ligand OX49L), – GITR - Treg (ligand GITRL – mainly APC) • Inhibitory – CTLA-4 expressed on activated T-lymphocytes, Treg (ligand CD80,86) , – PD-1 expressed on activated T-lymphocytes (ligand PDL1, PDL2,- activated macrophages, granulocytes) CTLA-4 • Expressed mainly on the surface of activated helper T cells. • Transmits an inhibitory signal to T-cells. • Similar to the T-cell co-stimulatory protein,CD28 both molecules bind to CD80 and CD86, (B7-1 and B7-2) • Intracellular CTLA4 is also found in regulatory T-cells and may be important to their function. • CTLA-4 binds its ligands, captures them from the surface of APC and internalizes them via a process that is called transendocytosis, leading to a reduction of APC-mediated T cell activation. • Ipilimumab – monoclonal antibody that blocks CTLA-4 function, is used for „stimulation“ of immune system during immunotherapy of several tumors. • Abatacept – fusion protein IgG+CTLA-4 – binds CD80/86, prevents T-cell activation, is used as immunosuppressive agent. Vazba CTLA-4 na CD80/86 vede k inhibici funkce T-lymfocytů PD-1 (Programmed cell death protein-1) • Expressed on activated T-lymphocytes • Binding to is ligands (PD-L1, PD-L2, expressed mainly on activated macrophages, granulocytes, dendritic cells) leads to apoptosis of antigen specific lymphocytes. • An important check-point in T-cell regulation. • PD-L1 is expressed on many cancer cells. • Monoclonal antibody against PD-1 (e.g. nivolumab) is used in immunotherapy of tumors. Regulation by antibodies • Negative regulation after IgG binding to FcgRII on B- cells. • Binding of the immune complex during the presentation of antigens by dendritic follicular cells to B-lymphocytes in germinal centers significantly increases immunogenicity. Inhibition of B-cells by antigen-antibody complexes Antigen Antigen IgG IgG Fc-receptor CD32B(FcR-II) BCR Associated proteinkinazesProtein phosphatase AKTIVACE Cell membrane Cytokines • Mediators, „tissue hormons“, main regulators of the cells of the immune system. • Produced mainly by the cells of the immune system, also the cells of the immune system predominate as the target cells. • The effect on the target cell is based on the interaction with specific receptors. • Usually short half-life • Nomenclature: – IL-1 - IL-36 (?) – Historical names: interferons, TNF, CSF.. Cytokines • Usually produced by a broad range of cells, bus some cells are usually „main producers“ of the concrete cytokine.. • Pleiotropic effect. • Cytokine network is formed. • A concrete cytokine may have both stimulatory and inhibitory effect, depending on the the interaction with other cytokines, concentration of the cytokine…. JAK-SAT signalisation plays a crucial role in signal transduction from cytokine receptors A roman god JANUS had two faces Effect of cytokines on cells Autokrine Receptor Parakrine Endokrine Signal Cytokine production Blood Effects of cytokines • Pro-inflammatory cytokines: IL-1, IL-6, TNF-a, IL-18 • Stimulation of macrophages: IFN-g • Stimulation of granulocytes: IL-8 • T-lymphocytes stimulation: IL-2 • B-lymphocytes stimulation, production of antibodies: IL-4, IL-5, IL-6, BAFF • Progenitor cells proliferation: IL-3, GM-CSF, M-CFS • Negative regulators: IL-10, IL-13, TGF-b Interferons (IFN) • Type I: IFN a, IFN b : produced by the virus infected cells (fibroblasts, macrophages). In the target cells they inhibit viral replication. • Type II „Immune“: IFN g: produced by activated TH1 cells, causes activation of macrophages. Chemokines • Low molecular weight polypeptides. • Based on the concentration gradient, they control migration of inglammatory cells to sites of inflammation (inflammatory chemokines). • Chemokineds regulate migration of cells even in physiological conditions (homeostatic chemokines). • They can also affect other functions of vatious cells of the immune system. • According to the location of cysteines at the N-terminus, they are divided into 4 families: CC, CXC, CX3C and C. • About 45 chemokines and 19 different chemokine receptors have been described.. • . Chemokines in anti-tumor response Cytokines in pathogensis of diseases • Atopic diseases: IL-4 stimulates IgE production, IL-5 stimulates eosinophils production. • Inflammatory diseases (rheumatic, Crohn´s disease), systemic response in sepsis – various pro-inflammatiory cytokines, TNF-a seems to be the most important. • Immunodeficiency diseases may be caused by disturbed production of various cytokines (IFNg, IL-12), or defect of cytokine receptors. Therapeutic use of cytokines • IFN-a: anti-tumor treatment (malignancies of the lymphatic system, renal cancer, treatment of hepatitis B and C • IL-2- anti-tumor treatment • GM-CSF – treatment of granulocytopenia • IFN-b: treatment of multiple sclerosis • IFN-g: treatment of some immunodeficiencies Anti-cytokine treatment • Blockade of function of cytokines by various approaches: – Direct blockade of cytokines. – Blockade of cytokine receptors. – Soluble artificial receptors binding cytokines. • Most frequently monoclonal antibodies, various fusion proteins… • Anti-inflammatory treatment: directed against TNF-a, IL- 1, IL-6, IL-17, IL-23.. • Anti-tumor treatment – blockade of various growth factors (e.g. EGF)