Basic Immunology and Multiple Sclerosis
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Basic Immunology and Multiple Sclerosis Ben Thrower M. D. Shepherd MS Institute Atlanta, GA Why Immunology? disease. • MS is an autoimmune disease • Existing and future therapies work by modulating or suppressing the immune system. References 1. AK 1 Abbas AK, Lichtman AH AH. Basic Immunology: Functions and System. W.B. Disorders of the Immune System W B Saunders Company. 2001. 2. Sospedra M M ti R A 2 S d M, Martin R. Annu. R Rev. Immunol. 2005; 23: 683-747. Immunology is like an onion ….. it s ….. not because it’s stinky and makes you want to cry….. layers. ….. but because there are lots of layers Overview of the Immune System Immune System Adaptive Innate (Specific) (Nonspecific) o line of defense 2 1o line of defense Protects/re-exposure Cellular Humoral Cellular Humoral Components Components Components Components Function of the Immune System (Self/Non-self Di (S lf/N i i ti ) lf Discrimination) • To protect from pathogens • ( g Intracellular (e.g. viruses and some bacteria and parasites) • Extracellular (e.g. most bacteria, fungi and parasites) • To eliminate modified or altered self Effects of the Immune System • Beneficial: • Protection from invaders • Elimination of altered self • Detrimental: • Discomfort and collateral damage (inflammation) (i fl ti ) • Damage to self (hypersensitivity or autoimmunity) Innate (Nonspecific) Immunity Innate Host Defenses Against Infection I f ti • Anatomical barriers – Mechanical factors – Chemical factors – Biological factors • Humoral components – Complement Coagulation system – C l ti t – Cytokines • Cellular components – Neutrophils – Monocytes and macrophages – NK cells – Eosinophils The Adaptive Immune System • Cell-mediated Immunity (Cytotoxicity) • T cells • CD4+ (Th1 & Th2) • CD8+ • Humoral Immunity (Antibody production) • B Cells Comparison of Innate and Adaptive Immunity I it Innate Immunity Adaptive Immunity • No time lag • A lag period • Not antigen specific • Antigen specific • No memory • Development of memory Cells of the Immune System Immune System Myeloid Cells Lymphoid Cells Granulocytic Monocytic T cells B cells NK cells Neutrophils Macrophages Helper cells Basophils B hil Kupffer ll K ff cells S Suppressor cells ll Pl ll Plasma cells Eosinophils Dendritic cells Cytotoxic cells Immune Interactions • Cell Receptors Immune Interactions • Cell Receptors Endothelial Lining Immune Interactions • Cytokines – Powerful chemical substances that allow for interactions between cells of system the immune system. Immune Interactions • Chemokines – Chemicals used by one immune cell to attract another cell to an inflammation area of inflammation. Cells of the Immune System • Lymphocytes 1) B cells, T cells, cells. Natural killer (NK) cells 2) Have receptors for specific antigens. antigens 3) Key mediators of adaptive immunity. 4) Nomenclature based upon surface proteins called CD (cluster of differentiation). Cells of the Immune System • Antigen-presenting cells (APC) 1) Dendritic cells, macrophages, ll i li (CNS). B cells, microglia (CNS) 2) Capture of antigen for display to lymphocytes. Cytokines immunity, • Mediators involved in cellular immunity including hormone-like glycoproteins released by activated T cells and macrophages. co-stimulators • Some are co stimulators of T cells and T cell proliferation. T cells T-cells CD8 T cell APC Naïve T cell CD4 T cell CD4 T Helper Cells • Activation of macrophages • Activation, proliferation and differentiation of T and B lymphocytes Major Histocompatibility Complex (MHC) • Proteins expressed on the cell surface which play a role in the immune system autoimmunity. and autoimmunity • Referred to as HLA (human leukocyte humans. antigen) in humans Major Histocompatibility Complex (MHC) • MHC class I – present on all nucleated cells. Present antigen fragments to CD8 cells cells. • MHC class II – present on antigen (APC). presenting cells (APC) Present antigen to CD4 cells. CD4+ T Helper Cells MHC II – Major Histocompatibility Complex* CD4 APC TCR CD8 Immature CD4+/CD8+ T Cell * MHC = HLA (Human Lymphocyte Antigen) CD4+ T Helper Cells CD4 TCR CD8 Mature CD4+ Cell CD4 / APC Receptors CD4 TCR Class II MHC CD3 CD28 B7-1/B7-2 (CD80/CD86) LFA-1 ICAM -1 VLA-4 CD4 T Helper Cell APC Immunological Synapse” The “Immunological Synapse • The interaction between the TCR and MHC molecules is not strong • Accessory molecules stabilize the interaction – CD4/Class II MHC or CD8/Class I MHC – CD2/LFA-3 LFA 1/ICAM 1 – LFA-1/ICAM-1 Immunological Synapse” The “Immunological Synapse • Specificity for antigen resides solely in the TCR • The accessory molecules are invariant • Expression is increased i response i d in to cytokines Immunological Synapse” The “Immunological Synapse g g • Engagement of TCR and Ag/MHC is one signal needed for activation of T cells • Second signal comes from costimulatory molecules – CD28 on T cells interacting with B7-1 (CD80) or B7-2 (CD86) – Others • Costimulatory molecules are invariant CD4 / APC Receptors CD4 Costimulatory TCR Class II MHC p Receptor CD3 CD28 B7-1/ B7-2 LFA-1 ICAM -1 VLA-4 CD4 T Helper Cell APC CD4 / APC Receptors CD4 Adhesion TCR Class II MHC Receptors R t CD3 CD28 B7-1/ B7-2 LFA-1 ICAM -1 VLA-4 CD4 T Helper Cell APC CD4 / APC Receptors CD4 TCR Class II MHC g Integrins CD3 CD28 B7-1/ B7-2 LFA-1 ICAM -1 VLA-4 CD4 T Helper Cell APC Costimulation is Necessary for T Cell Activation • Engagement of TCR and Ag/MHC in h b f A /MHC i the absence of co- stimulation can lead to anergy • Engagement of co-stimulatory E t f ti l t molecules in the absence of TCR engagement results in no p response • Activation only occurs when both TCR and co-stimulatory molecules are engaged with their ti li d th i respective ligands • Downregulation occurs if CTLA- 4 interacts with B7 – CTLA 4 sends an inhibitory CTLA-4 inhibitor signal Key Steps in T cell Activation p • APC must process and p peptides to T cells present p p • T cells must receive a costimulatory signal – Usually from CD28/B7 • Accessory adhesion molecules help to stabilize binding of T cell and APC – CD4/MHC-class II or CD8/MHC class I LFA-1/ICAM-1 – LFA 1/ICAM 1 – CD2/LFA-3 • Signal from cell surface is transmitted to nucleus – Second messengers • Cytokines produced to help drive cell division – IL-2 and others Naïve CD4 T cells differentiate into TH1 and TH2 cells Naïve CD4 T cell Th1 Th2 Anti- Pro-inflammatory inflammatory Cytokines • IL-2 Cytokines • Il-12 Reciprocal Inhibition • IL-4 • IL-5 • IFN-γ • Il-10 • TNF • IL-13 • TGF-β (TH3) B cell Macrophage Yong, W CD4 Subsets CD4 T cell IL-12 IL 12 IL-6/IL-23 IL-4 CD4 CD4 Th1 cell CD4 Th17 cell Th2 cell Cells CD4 Th17 C ll • Recently described subset of CD4 cells. IL-17 TNF • Cytokines produced = IL 17 and TNF- alpha. Stimulated by IL-6 d IL-23 t ki • Sti l t d b IL 6 and IL 23 cytokine. Bettelli E, Carrier Y, Gao W, et al. Nature 2006; 441(7090):235-238. T cells T-cells CD8 T cell APC Naïve T cell CD4 T cell CD8 T Cells • Cytotoxic CD8 cells are the only T cells capable of killing other cells by direct contact. contact • CD8 cells may also serve a regulatory or role. suppressive role CD8+ T Cells MHC I – Major Histocompatibility Complex* CD4 APC TCR CD8 Immature CD4+/CD8+ T Cell * MHC = HLA (Human Lymphocyte Antigen) CD8+ T Cells TC Cytotoxic CD4 TCR CD8 TS Suppressor Mature CD8+ Cell CD8 / APC Receptors CD8 TCR Class I MHC CD3 CD28 B7-1/ B7-2 LFA-1 ICAM -1 VLA-4 CD8 T Cell APC Cytotoxic T Cell (Tc) , , y • TC cells, or killer T cells, are the only T cells that can directly attack and kill other cells • They circulate throughout the body in search of body ll h display h i hi h h b d cells that di l the antigen to which they have been sensitized • Their targets include: – Virus-infected cells – p Cells with intracellular bacteria or parasites – Cancer cells – Foreign cells from blood transfusions or transplants Mechanisms of Tc A ti M h i f Action • In some cases, TC cells: – Bind to the target cell and release perforin into its membrane • In the presence of Ca2+ perforin causes cell lysis by creating transmembrane pores • Other TC cells induce cell death by: – Secreting lymphotoxin, which fragments the target cell’s DNA – Secreting gamma interferon, which stimulates phagocytosis by macrophages B Cells • B cells may mature into antibody producing plasma cells. APC s. • B cells may function as APC’s B Cell – CD4 Th Interactions CD40 CD 40 Ligand CD4 Th B Cell TCR C ll Cell MHCII CD28 B7 Cytokine Receptor B Cell Proliferation CD4 Activation and Differentiation CD40 CD 40 Ligand CD4 Th B Cell TCR Cell C ll MHCII CD28 B7 Antibodies • Also called immunoglobulins – Constitute the gamma globulin portion of blood proteins – Are soluble proteins secreted by activated B cells and plasma cells in response to an antigen p g p y – Are capable of binding specifically with that antigen • There are five classes of antibodies: IgD, IgM, IgG, IgA, and IgE Natural Killer (NK) Cells antibody coated cells. • Bind to and kill antibody-coated cells • Called “natural killers” because they do not first. have to recognize antigen first g Immunological tolerance • Definition: – Specific immune unresponsiveness to an antigen that is induced by exposure of lymphocytes to that antigen (tolerogen vs immunogen) • Significance: – All individuals should be tolerant of their own antigens (self-tolerance); breakdown -->autoimmunity p – The induction of tolerance could be exploited to treat autoimmune diseases – Mechanisms of tolerance must first be understood Mechanisms of unresponsiveness to lf ti t self antigens • Central tolerance – Immature self-reactive T lymphocytes that recognize self g y g g antigens in the thymus undergo negative selection (deletion). • Peripheral tolerance Mature self-reactive T lymphocytes th t escape central –M t lf ti l h t that t l tolerance and recognize self antigens in peripheral tissues (anergy), ( ) g can be inactivated (anergy killed (deletion) or regulated gy), gy (suppressed). • “Clonal ignorance” – Mature self-reactive lymphocytes do not respond to self antigens in non-inflamed settings. Multiple Sclerosis What went wrong? Key Steps in the MS Process 1. 1 A breakdown in the ability to distinguish self from non-self. 2. 2 Upregulation of myelin reactive CD4 Th1 cells. 3. Increased permeability of the BBB. 3 I d bilit f th BBB 4. The role of B cells and CD8 cells. Requirements for the development of an autoimmune disease Nature Immunology (9): 759-761 (2001) HLA Type and MS Risk • Many autoimmune diseases in humans are linked to particular HLA alleles. • HLA DR2 and DR4 haplotypes are associated with an increased risk for MS. Environmental Factors • Many pathogens have been proposed to have a role in the pathogenesis of MS. HHV-6, EBV, • HHV 6 EBV Chlamydia pneumonia Molecular Mimicry • The pathogen contains similar peptide sequences to peptides found in myelin (MBP, MAG others). (MBP MAG, MOG others) • The pathogen may have similar three- di i l t t th t t dimensional structures that promote cross- reactive immunity. Immune Dysfunction in MS • Myelin autoreactive CD4 cells may have less of a need for co-stimulation to become activated in a person with MS MS. • Downregulation of CD4 cells via CTLA-4 MS. may be impaired in MS Innate and Adaptive Immune Responses TLR (Toll Like Autoreactive Cytokines Receptor) CD4/CD8 Pathogen Innate Immune Cell I t I C ll Naïve CD4 T cells differentiate into TH1 and TH2 cells Naïve T cell Th1 Th2 Anti- Pro-inflammatory inflammatory Cytokines • IL-2 Cytokines • Il-12 Reciprocal Inhibition • IL-4 • IL-5 • IFN-γ • Il-10 • TNF • IL-13 • TGF-β (TH3) B cell Macrophage Yong, W Th1 / Th2 Imbalance Th1 Th2 Normal Th1 / Th2 Imbalance MS Increased BBB Permeability increased, • Some chemokine levels are increased leading to increased adhesion and attraction of autoreactive T cells into the CNS. • Increased production of matrix metalloproteinase leads to increased BBB permeability. permeability The Role of B Cells in MS • Increased immunoglobulin (Ig) production in the CSF, but not the serum. • CSF Ig in MS shows an oligoclonal distribution, i.e. a limited number of B cell production. clones contribute to the Ig production How Do B Cells and Ab Contribute h Pathogenesis i MS? to the P h i in APC’s • B cells may serve as APC s for autoreactive T cells. • B cells provide costimulation for autoreactive T cells. ll help it t ti • B cells may h l recruit autoreactive T cells into the CNS. • B cells produce myelin-specific autoantibodies that destroy myelin. The Role of CD8 Cells in MS • Cells in the CNS express MHC I much more so than MHC II. Myelin-reactive • Myelin reactive CD8 cells are more common than myelin-reactive CD4 cells in tissue MS brain tissue. • Myelin-reactive CD8 cells secrete h ki for li ti ll chemokines f myelin-reactive CD4 cells. Mechanism of Action of Current Therapies • Glatiramer acetetate • Beta interferons • Natalizumab MOA: Glatiramer acetate (GA) • Anti-inflammatory effects – Th2/ T ll Treg cells • GA promotes the development of Th2 and Treg cells • Release anti-inflammatory cytokines reducing the activity of Th1 cells in the periphery and CNS – Innate immune effects • Direct effect on monocytes/APCs yielding anti- inflammatory cytokine producing phenotype • Polarizes CD4+ T cell development down a Th2 and Treg path CD8 – Possible role for regulatory CD8+ cells • Induces a population of GA-reactive CD8+ T cells that can suppress or even kill CD4+ T cells Weber MS, et al. Neurotherapeutics. 2007;4:647-53., Arnon R, et al. Mol Neurobiol. 2007;36:245-53. MOA: Glatiramer acetate (GA) p • Enhanced reparative p processes – Neurotrophic factors • GA reactive cells and resident CNS cells produce BDNF, NT-3/4, IGF-1, and GDNF – Remyelination • Increases proliferation, differentiation, and survival of OPCs – Neurogenesis • Augments neuronal progenitor cell proliferation, differentiation, and migration to sites of damage; axonal sprouting noted Weber MS, et al. Neurotherapeutics. 2007;4:647-53., Arnon R, et al. Mol Neurobiol. 2007;36:245-53. MOA: GA MOA: GA MOA: GA IFN β may shift T cells from a pro-inflammatory to y profile in the p p y an anti-inflammatory p periphery IFN β IL-4, IL-10, IL-131,2 Th2 IFN-α/βR T cells T suppressor Activity3 X IFNγ4 Th1 1. Mei E, et al. J Neurol Sci 2006; 246(1-2): 71-7 2. Wiesemann E, et al. J Neuroimmunol 2002; 123(1-2): 160-9 3. Noronha A, et al. Ann Neurol 1990; 27(2): 207-10 4. Sega S, et al. Clin Neurol Neurosurg 2004; 106(3): 255-8 IFN β decreases adhesion molecule and MMP expression, blocking T-cell migration across the BBB p g g Periphery BBB CNS Increase in soluble IFN β adhesion molecules sVCAM-11 MMP-9 is required VLA4/VCAM-1 VLA4/VCAM 1 for migration of T cells through the X basement membrane of the BBB2-4 IFN β Activated VLA4 T cell Decreased MMP-9 1. Trojano M, et al. Neurology 1999; 53(7): 1402-08 j , gy ; ( ) Downregulation of 2. Nelissen I, et al. Brain 2003; 126(Pt6): 1371-81 VLA4 in T cells5,6 sVCAM-1 (decoy) 3. Stone LA, et al. Ann Neurol 1995; 37(5): 611-19 4. Stuve O, et al. Ann Neurol 1996; 40(6): 853-63 VCAM-1=vascular cell adhesion molecule ; VLA-4=very 5. Soilu-Hanninen M, et al. J Neuroimmunol 2005; 167(1-2): 175-82 late antigen 4; MMP-9=matrix metalloproteinase 9 6. Murano PA, et al. J Neuroimmunol 2000; 111(1-2): 186-94 Natalizumab MOA Natalizumab Thanks!