CENTRAL TOLERANCE IS INDUCED AND MAINTAINED IN THE THYMUS Clonal deletion of self agressive B and T cell clones (not complete) B AND T CELLS WITH SELF REACTIVITY ARE PRESENT IN THE AVAILABLE PERIPHERAL T CELL REPERTOIRE PERIPHERAL TOLERANCE Maintenance of self tolerance of T-lymphocytes against tissue- specific self proteins which are not represented in the thymus Active mechanisms at the level of CD4+ helper T-lymphocytes AUTOIMMUNE DISEASES Disturbance of tolerance Misdirected adaptive immunity to healthy cells and tissues

Normal tissue cells do not express MHC class II NO SIGNAL 1. for CD4+ Th activation Normal tissue cells do not express co-stimulatory molecules and do not produce T cell differentiating cytokines NO SIGNAL 2. for CD4+ Th activation Migration of naive T lymphocytes to normal tissues is limited Antigen presenting cells are not activated in normal tissues NO SIGNAL 3. for CD4+ Th activation PERIPHERAL TISSUES TOLERIZE THEMSELVES PERIPHERAL TOLERANCE IMMUNE RESPONSES ARE NOT INITIATED IN THE PERIPHERY

ANERGY – Functional unresponsiveness, no IL-2 secretion SIGNAL 1 Recognition of auto-antigen on tissue cell SIGNAL 2 No B7 and CD40 expression, no co-stimulation Tissue resident professional APC are not activated SIGNAL 3 Innate immunity is not activated No inflammation CLONAL DELETION – Activation induced cell death Requires persistant high antigen dose Fas – FasL interaction SUPPRESSION – Activity of other cells Cytokine-mediated balance Effector functions are inhibited by regulatory T cells CLONAL IGNORANCE No contact with the immune system Immunologically privileged sites Central nervous system, eye No recognition in the periphery MECHANISMS OF PERIPHERAL TOLERANCE

NEGATIVE REGULATION OF THE IMMUNE SYSTEM

NEGATIVE REGULATION IN THE IMMUNE SYSTEM 1.Decrease of antigen concentration in the course of the immune response 2.Inhibition of B lymphocyte activation - antibody feedback Cross linking of BCR with Fc  RIIB (CD32) by antigen-antibody complex ITIM-induced negative signaling of B cell activation - phosphatases B cells without T cell help are excluded from follicles 3.Death of activated T lymphocytes Passive cell death mediated by the shortage in survival factors (cytokines) Activation induced FasL expression sensitizes activated T cells for Fas- mediated apoptosis (AICD) Activation induced cell death (AICD) is induced by repeated antigenic stimulation 4. Inhibition T lymphocyte activation Anergy of CD4+ T lymphocytes Late in the immune response activated T cells express CTLA-4, the ligand of B7 4.Suppression by regulatory T lymphocytes Counter regulation of Th1 and Th2 cytokines Production of suppressive cytokines IL-10 inhibits APC function such as IL-12 secretion and B7 expression TGF  inhibits T-cell proliferation IL-4 inhibits IFN  -mediated functions IL-10 and TGF  inhibit macrophage activation

NEGATIVE REGULATION OF IMMUNE RESPONSES Naive lymphocytes Number of antigen specific cells Primary effectors Secondary effectors Memory DIFFERENTIATION AICD EXPANSION AICD MEMORY

Iγ-γIγ-γ FcγRI (CD64)FcεRIIFcγRII (CD32) IIIaζ-ζ IIIaζ-γ IIIaγ-γ IIIaβ α β γ-γ α γ-γ γ-γ α FcεRI FcγRIII (CD16) IMMUNOGLOBULIN BINDING Fc RECEPTORS IgG Fc receptors Fc  RI Ig supergene family, MIRR

ITAM ITIM NEGATIVE REGULATION OF B LYMPHOCYTES BY IMMUNE COMPLEXES Fc  RIIb

ACTIVATING AND INHIBITORY RECEPTORS IN THE IMMUNE SYSTEM Activating receptor ITAM ExpressionInhibitory receptor ITIM Expression Fc receptorok Ig supergene family BCR  * B cell TCR ,  * CD3  * T cell Fc  RIa (CD64) Fc  RI  * Macrophage, DC (internalization) Fc  RIIa (CD32) Macrophage, DC (internalization) Fc  RIIb (CD32) B cell Fc  RIIIa (CD16) Fc  RI  * vagy  * NK cell (ADCC) Fc  RI, Fc  RI  * Mast cell (ADCC) C-type lectin Fc  RIIb (CD23b)Fc  RIIa (CD23a) B cell MHC I receptorok Ig supergene familyHuman KARHuman KIRNK and T cell C-típusú lektinEgér KIR Human NKG2C/DNK and regulatory T cellHuman NKG2A/BNK and regulatory T cell Other receptors BCRCD22B cell CD28CTLA-4T cell  MIRR Multisubunit Immune Recognition Receptors  The ligand binding and signal transducing subunits are separated, they co-localize in membrane microdomains.

CD28 Activated T cell CD28 cross linked by B7 Costimulatory molecules also associate with inhibitory receptors CTLA-4 binds CD28 with a higher affinity than B7 molecules /CTLA-4 B7 CD28 T cell B7 22 Signal 1 + Co-stimulation induces CTLA-4 The lack of signal 2 to the T cell shuts down the T cell response. Cross-linking of CTLA-4 by B7 inhibits co-stimulation and inhibits T cell activation -----

NEGATIVE REGULATION OF T CELL ACTIVATION BY CTLA-4 CTLA-4 CD28 B7 LATE EXPRESSION HIGHER AFFINITY TO B7 THAN CD28 T APC

THE ROLE OF CD4+ T CELLS IN APOPTOSIS T CELL HOMEOSTASISSHUT OFF IMMUNE RESPONSES

REGULATORY T CELLS

Treg CD25 IL-2Rα CTLA4 B7 ligand GITR MARKERS OF THYMUS DERIVED NATURAL Treg CELLS CD127 IL-7Rα ↓ Treg differentiation, maintenance, function Transcription factor – many target genes Itself is not sufficient to confer suppressive function A TGFβ does not induce regulatory function FoxP3 CD4 + CD25 + FOXP3 + REGULATORY T CELLS

FUNCTIONS OF REGULATORY T CELLS Maintenance of peripheral tolerance Prevention of autoimmunity Limiting inflammatory processes (asthma, inflammatory bowel diseases) Inhibit protection against infectious diseases Limit immune responses to tumors MECHANISM Intrinsic and extrinsic regulation Various inhibitory mechanisms Cell contacts – Cytokines Interaction with the target effector T cells

REGULATORY FUNCTION OF REGULATORY T LYMPHOCYTES IL-35 Inhibitory cytokines TGFβIL-10 Cytolysis Metabolic dysregulationInhibition of dendritic cell maturation Descreased cytokine production (IL-2) Adenosin around the cell cAMP transfer Indolamin2,3-dioxigenase LAG-3 – CD4 homolog Treg : effektor T cell = 1 : 8 Treg : DC = 1 : 0,8

THE ROLE OF IL-35 IN THE FUNCTION OF REGULATORY T CELLS Induced capability, the effector cell is involved NOT ONLY A FUNCTION The molecular patterns of activated Treg cells are different in the presence and absence of effector cells The expression of EBI3 and IL-12α/p35 (IL-35) subunits is increased in the presence of effector T cells Treg cells in contact with effector cell act also on effector cells out of contact through IL-35 Initial T cell activationSensed by Treg cells Increased suppressive mechanisms

TOLERANCE AND AUTOIMMUNITY STRONG IMMUNE RESPONSES TO FOREIGN ANTIGENS WHILE SUSTAINED TOLERANCE TOWARD HUMAN MACROMOLECULES AUTOIMMUNE DISEASES Complicated multifactorial diseases No single entity can be identified as the necessary and sufficient cause of a particular disease Unlucky combination of genetic and environmental factors Side effect of successfully fighting against infections

DiseaseHLA serotype Relatív riskSex ratio Women/male Ankylosing spondylitisB Acute anterior uveitisB <0.5 Goodpasture’s syndromeDR215.9~1 Multiple sclerosisDR Graves’s diseaseDR Myasthenia gravisDR32.5~1 Systemic lupus erythematosusDR Insulin dependent diabetes mellitus DR3 and DR4 3.2~1 Rheumatoid arthritisDR44.23 Pemphigus vulgarisDR414.4~1 Hashimoto thyroiditisDR ASSOCIATIONS OF HLA ALLOTYPE WITH SUSCEPTIBILITY TO AUTOIMMUNE DISEASE Maximum 20% of predisposed people develop the disease  environmental factors

Chronic inflammatory conditions Repair mechanisms cannot compete with tissue destruction caused by the immune system Variety of symptoms and of target tissues 2 – 3% of the population, females are more commonly affected Mechanisms of recognition and effector functions are the same as those acting against pathogens and environmental antigens Both genetic and environmental factors are involved in the pre- disposition to autoimmune diseases –HLA class I and II and other genetic factors affect susceptibility Runs in families and varies between populations C1, C2 or C4 deficiency predisposes to systemic lupus erythematosus (SLE) –Environmental factors Goodpasture’s syndrome – autoantibodies to type IV collagen, glomerulonephritis, smokers develop pulmonary hemorrhage as well Symphathetic ophtalmia – provoked by demage Infection – Wegener’s syndrome – antibodies to proteinase-3 of neutrophil granules results in destruction of small blood vessels primarily in the lung Any infection can induce granulocyte activation and exposure of the autoantigen AUTOIMMUNE DISEASES

TISSUE-SPECIFIC AUTOIMMUNE DISEASES Endocrine glands Tissue-specific proteins are not expressed in other cells Vascularized tissues, secrete hormone to the blood –Easy access to the immune system Impaired function of a single type of epithelial cells Thyroid gland –Hashimoto’s thyroiditis no thyroid hormone production – hypothyroid CD4+ T cells and antibodies against thyroglobulin and microsomal proteins –Graves’ disease Antibodies to TSH receptor – hyperthyroid Negative feedback regulation is not functional CD4+ Th2 cells and antibodies against the muscle of eye – bulding eyes Islets of Langerhans in pancreas –Insulin-dependent diabetes T cells against insulin, glutamic acid decarboxylase GAD –Insulin-resistant diabetes Antagonistic antibodies to insulin receptor Adrenal gland –Addison’s disease – chronic adrenal gland hypofunction Lymphocyte infiltration

DISEASES MEDIATED BY ANTIBODIES AGAINST CELL SURFACE RECEPTORS Type II hypersensitivity SyndromeAntigenAntibodyConsequense Grave’s diseaseThyroid stimulating hormon receptor AgonistHyperthyroidism Myasthenia gravisAcetylcholine receptor AntagonistProgressive muscle weakness Insulin resistant diabetes Insulin receptorAntagonistHyperglycemia, ketoacidosis HypoglycemiaInsulin receptorAgonistHypoglycemia Grave’s disease – signaling through the TSH receptor the disease is transferred to the fetus by antibodies can be cured by plasmapheresis Myasthenia gravis – internalization and degradation of the receptor

PITUIARY Tyroid stimulating hormon TSH PITUIARY Tyroid hormons T3/T4 HYPERTYROSIS STIMULATING ANTIBODIES IN GRAVES’ DISEASE Tyroid hormons T3 triiodine tyronin T4 tyroxin Tyroglobulin Folliculus lumen NEGATIVE FEED BACK

Nerve impulse Internalization NO Na+ influx NO muscle contraction MIYSTENIA GRAVIS BLOCKING AUTO – ANTIBODIES IN MYASTENIA GRAVIS NEURO-MUSCULAR JUNCTION Muscle Acetilcholin receptor Degradation

Insulin  cell  cell  cell  cell  cell Pancreatic islet cells MECHANISM OF AUTOREACTIVITY IN INSULIN- DEPENDENT DIABETES Type IV hypersensitivity AUTOREACTIVE CYTOTOXIC T CELLS KILL INSULIN SECRETING β-CELLS glucagon Somatostatin 10 8 insulin secreting cells

SYSTEMIC AUTOIMMUN DISEASES Autoreactivity against common components of human cells Systemic lupus erythematosus SLE –Type III hypersensitivity –Autoantibodies against cell surface, cytoplasmic, nuclear proteins, nucleic acid, nucleoprotein particles induce tissue demage –Comon nucleoprotein particles Nucleosome Splicosome Small cytoplasmic ribonucleoprotein complex – Ro, La –Soluble cellular antigens bind antibodies and form soluble immune complexes – released form dying, dead cells –Immune complexes are deposited to blood vessels,kidneys, joints and other tissues Rheumatoid arthritis – Type IV hypersensitivity –Cellular response to synovial membrane CD4+ and CD8+ T cells, B cells, plasma cells, neutrophils, macrophages Production of rheuma factors – antibodies to IgG-Fc

FACTORS INVOLVED IN THE PATHOMECHANISM OF AUTOIMMUNE DISEASES Lack of AICD – mediated clonal deletion –mutation in Fas or FasL Block of anergy –induced by tissue necrosis or local inflammation  breaking T cell anergy by increased B7 expression Novel Th epitope  self reactive B cell activation  drug induced hemolytic anemia Inefficiency of regulatory T cell function Molecular mimicry –cross reactivity of pathogenic and self proteins Polyclonal lymphocyte activation –LPS, superantigens Immunologically previledged sites  Damage of anatomical barriers –Post-traumic uveitis Exposure of cryptic antigens, determinants, sub-dominant epitopes  Damage of molecular barriers – APC function, pathogenic enzymes ANY CHANGE DISTURBING THE PHYSIOLOGICAL THRESHOLD

ASSOCIATION OF INFECTION WITH IMMUNE- MEIDATED TISSUE DEMAGE InfectionHLA associationConsequence Group A Streptococcus?Rheumatic fever carditis, polya-arthritis Chlymydia thrachomatisHLA-B27Reiter’s syndrome arthritis Shigella felxneri Salmonella typhimurium Salmonella enteritidis Yersinia enterocolitica Campylobacter jejuni HLA-B27Reactive arthritis Borella burgdorfeiHLA-DR2, DR4Chronic arthritis in Lyme disease

Type II HYPERSENSITIVITY IgG antibodies bound to cell surface or tissue antigen Antigen expressing cells – become sensitive to complement- mediated lysis and/or opsonized phagocytosis Frustrated phagocytosis  tissue damage Antibodies inhibit or stimulate cell functions no tissue damage HYPESENSITIVITY REACTIONS caused by IMMUNCOMPLEXES Type II and III

Cell Peptide modified by drug Th B IgG type antibodies MECHANISMS OF DRUG SENSITIVITY

„Butterfly„ flush on the face - discoid lupus erythematosus (DLE) – skin manifestation systemic lupus erythematosus (SLE) Chronic inflammation in SLE upper dermis. Vacuolized and disintegrated basal layer, flushing purpura containing erythrocytes. TYPE III HYPERSENSITIVITY IN SLE

Immunofluorescent staining with anti- complement antibody. IC deposition takes place at the dermal – epidermal border. Immunofluorescent staining with anti-IgG antibody. IMMUNE COMPLEX DEPOSITION IN THE SLE SKIN

Glomerulus in lupus nephritis. Lupus nephritis KIDNEY LESIONS IN RHEUMATIC DISEASES