Antigens and Antibodies PDF

Antigens and Antibodies Copyright ©2018, Elsevier Inc. All rights reserved.  Learning Objectives At the conclusion of this chapter, the reader should be able to ˜ define the terms antigen and antibody. ˜ compare the characteristics of major histocompatibility complex (MHC) classe...

Antigens and Antibodies Copyright ©2018, Elsevier Inc. All rights reserved.  Learning Objectives At the conclusion of this chapter, the reader should be able to ˜ define the terms antigen and antibody. ˜ compare the characteristics of major histocompatibility complex (MHC) classes I and II. ˜ differentiate the characteristics of each of the five immunoglobulin classes. ˜ draw and describe a typical immunoglobulin G (IgG) molecular structure. Copyright ©2018, Elsevier Inc. All rights reserved. 2  Learning Objectives (Cont.) ˜ compare the differences between isotype, idiotype, and allotype. ˜ name the four phases of an antibody response. ˜ describe the characteristics of a primary and secondary (anamnestic) response. ˜ compare the terms antibody avidity and antibody affinity. ˜ describe the method of production of a monoclonal antibody. Copyright ©2018, Elsevier Inc. All rights reserved. 3  Learning Objectives (Cont.) ˜ correctly answer case study-related multiple choice questions. ˜ analyze a patient history, clinical signs and symptoms, and laboratory date; answer the related multiple choice and critical thinking questions, and conclude the most likely diagnosis. ˜ describe the principal and agglutination reactions in ABO blood grouping. ˜ correctly answer end-of-chapter review questions. Copyright ©2018, Elsevier Inc. All rights reserved. 4  Antigen Characteristics ˜ Immunogen Ø A macromolecule capable of triggering an adaptive immune response and then reacting with the antibodies produced ˜ Antigen Ø Any substance that may be specifically bound by an antibody molecule or T-lymphocyte receptor ˜ Hapten Ø A lower molecular weight molecule that can bind to an antibody but must be attached to a macromolecule as a carrier to stimulate a specific immune response Copyright ©2018, Elsevier Inc. All rights reserved. 5  An$gen vs. Immunogen An$gen Immunogen – Any substance that – Any substance that can bind to an can elicit an an$body or T cell immune response receptor – All immunogens are an$gens – Not all an$gens are immunogens, i.e. haptens  Epitope ˜ As part of an antigen reacts specifically with an antibody or T-lymphocyte receptor ˜ Only prominent determinants on the surface of the antigen will be recognized by the immune system Copyright ©2018, Elsevier Inc. All rights reserved. 7  Histocompatibility Antigens ˜ Major histocompatibility complex (MHC) ˜ Referred to as human leukocyte antigens (HLAs) Copyright ©2018, Elsevier Inc. All rights reserved. 8  Immunogenicity of An$gens Determined by Influenced by – Foreignness – Host genotype – Molecular Size – Dose and route of – Chemical administra$on Composi$on – Presence of – Degradability adjuvants  Immunogenicity of An$gens Determined by Influenced by – Foreignness – Host genotype – Molecular Size – Dose and route of – Chemical administra$on Composi$on – Presence of – Degradability adjuvants Factors Influencing Immunogenicity Foreignness Size Chemical Composition Sequence determinants – Primary Structure – Secondary Structure Conformational determinants – Tertiary Structure – Quarternary Structure Suscep$bility to Ag processing&presenta$o (Degradability)  Gene$cs – Species – Individual Responders vs Non-responders Age Dose Route – Subcutaneous > Intravenous > Intragastric Adjuvant – Substances that enhance an immune response to an Ag Func$ons: Prolong Ag persistence Enhance co-s$mulatory signals Induce granuloma forma$on S$mulate lymphocyte prolifera$on non-specifically Examples: 1): Aluminum Potassium Sulfate (Alum) + An%gen Conclusion: - Salt will ppt the ag, slower release and Increase %me of exposure - Increase the size of Ag to enhance phagocytosis 2) Freund’s adjuvant a- Freund’s Incomplete Adjuvant (FICA) Ag in aqueous solution + mineral oil + emulsifying agent: Slow releaes of ag due to oil droplets surrounding the ag b- Freund’s Complete Adjuvant (FCA) heat killed Mycobacteria + in water- in oil emulsion: cell wall of bacteria to enhance phagocytosis Chemical Nature of Immunogens Proteins Polysaccharides Nucleic Acids Lipids – Some glycolipids and phosopholipids can be immunogenic for T cells and illicit a cell mediated immune response  Types of An$gens T-independent Properties – Polymeric structure – Polyclonal B cell activation Yes -Type 1 (TI-1) No - Type 2 (TI-2) – Resistance to degradation Examples – Pneumococcal polysaccharide, lipopolysaccharide – Flagella  Types of An$gens T-dependent Proteins Structure Examples – Microbial proteins – Non-self or Altered- self proteins  An$genic Determinants Recognized by B cells and Ab Composi$on – Proteins, polysaccharides, nucleic acids, haptens – Sequence (linear) determinants – Conforma$onal determinants Size – 4-8 residues F e  An$genic Determinants Recognized by T cells Composi$on – Proteins (some lipids) – Sequence determinants Processed MHC presenta$on (lipid presenta$on by MHC-like CD1) Size – 8 -15 residues Number – Limited to those that can bind to MHC  Superan$gens Definition: any substance that bind to Vβ domain of T cell— Activation Examples – Staphylococcal enterotoxins – Staphylococcal toxic shock toxin – Staphylococcal exfoliating toxin – Streptococcal pyrogenic exotoxins  Determinants Recognized by the Innate Immune System ˜ PAMPs – Pathogen Associated Molecular Patterns ˜ PRRs – Pattern Recognition Receptors  Biological PAMP PRR Consequence of Interaction Microbial cell wall Complement Opsonization; components Complement activation Mannose- Mannose-binding Opsonization; containing protein Complement carbohydrates activation Polyanions Scavenger receptors Phagocytosis Lipoproteins of TLR-2 (Toll-like Macrophage Gram+ bacteria receptor 2) activation; Yeast cell wall Secretion of components inflammatory cytokines  Biological PAMP PRR Consequence of Interaction Double stranded TLR-3 Production of RNA interferon (antiviral) LPS TLR-4 Macrophage (lipopolysaccharide activation; of Gram– bacteria Secretion of inflammatory cytokines Flagellin (bacterial TLR-5 Macrophage flagella) activation; Secretion of inflammatory cytokines  Biological PAMP PRR Consequence of Interaction U-rich single TLR-7 Production of stranded viral RNA interferon (antiviral) CpG containing TLR-9 Macrophage DNA activation; Secretion of inflammatory cytokines THANKS Kindt Goldsby Osborne Kuby IMMUNOLOGY Immunoglobulins: Structure and Function Copyright © 2007 by W. H. Freeman and Company  TEACHING OBJECTIVES: 1. To discuss the general properties of all immunoglobulins 2. To describe the basic structure of immunoglobulins 3. To relate immunoglobulin structure with function 4. To define immunoglobulin hypervariable and framework regions 5. To define immunoglobulin classes and subclasses, types and subtypes 6. To describe the structures and properties of immunoglobulin classes  Immunoglobulins = Antibodies Igs = Abs q Primary function: 1- Combine with Ag, 2- Neutralize bacterial toxins 3- or viruses q Seconday interaction: Ab + Complement (in large Ag as bacteria) q In Diagnosis: Ig concentration: In infectious and autoimmune diseases q Presence & Concentartion determination: Serology II Copyright © 2014, 2009, 2003, 1996, 1990 by 36 Mosby, an imprint of Elsevier Inc.. Immunoglobulins:Structure and Function ˜ Definition: Glycoprotein molecules that are produced by plasma cells in response to an immunogen and which function as antibodies + - albumin Amount of protein globulins α1 α2 β γ Immune serum Ag adsorbed serum Mobility General Characteristics of Antibodies ˜ Specific proteins referred to as immunoglobulins ˜ Isolated in the gamma globulin fraction of protein by electrophoretic separation ˜ Primary function to combine with corresponding antigen Copyright ©2018, Elsevier Inc. All rights reserved. 39  Basic Immunoglobulin Structure ˜ Immunoglobulins - heterogeneous ˜ Myeloma proteins - homogeneous immunoglobulins  Antibody Structure ˜ Typical immunoglobulin molecule Ø Heavy chains Ø Light chains Copyright ©2018, Elsevier Inc. All rights reserved. 41  Immunoglobulin Classes ˜ IgM ˜ IgG ˜ IgA ˜ IgD ˜ IgE Copyright ©2018, Elsevier Inc. All rights reserved. 44  Human Immunoglobulin Classes ˜ IgG - Gamma (γ) heavy chains ˜ IgM - Mu (µ) heavy chains ˜ IgA - Alpha (α) heavy chains ˜ IgD - Delta (δ) heavy chains ˜ IgE - Epsilon (ε) heavy chains Human Immunoglobulin Subclasses ˜ IgG Subclasses Ø IgG1 - Gamma 1 (γ1) heavy chains Ø IgG2 - Gamma 2 (γ2) heavy chains Ø IgG3 - Gamma 3 (γ3) heavy chains Ø IgG4 - Gamma 4 (γ4) heavy chains ˜ IgA subclasses Ø IgA1 - Alpha 1 (α1) heavy chains Ø IgA2 - Alpha 2 (α2) heavy chains Human Immunoglobulin Subclasses ˜ IgG Subclasses Ø IgG1 - Gamma 1 (γ1) heavy chains Ø IgG2 - Gamma 2 (γ2) heavy chains Ø IgG3 - Gamma 3 (γ3) heavy chains Ø IgG4 - Gamma 4 (γ4) heavy chains ˜ IgA subclasses Ø IgA1 - Alpha 1 (α1) heavy chains Ø IgA2 - Alpha 2 (α2) heavy chains Antibody Structure—IgG Copyright ©2018, Elsevier Inc. All rights reserved. 50  IgG molecule Used with permission from: Dr. Mike Clark, Immunology Division, Department of Pathology Cambridge University, Cambridge, England  IgG ˜ Structure Ø Monomer (7S) IgG1, IgG2 and IgG4 IgG3  IgG ˜ Structure ˜ Properties Ø Major serum Ig (systemic immunity) Ø Major Ig in extravascular spaces Ø Placental transfer – Does not require Ag binding (± IgG2) Ø Fixes complement (± IgG4) Ø Binds to Fc receptors (± IgG2, IgG4) Phagocytes - opsonization K cells - ADCC Antibody Structure—IgM Copyright ©2018, Elsevier Inc. All rights reserved. 57  IgM J Chain ˜ Structure Ø Pentamer (19S) Ø Extra domain (CH4) Ø J chain Cµ4  IgM ˜ Structure ˜ Properties Ø 3rd highest serum Ig Ø First Ig made by fetus and B cells Ø Fixes complement Antibody Structure—IgA Copyright ©2018, Elsevier Inc. All rights reserved. 60  IgA ˜ Structure Ø Serum - monomer Ø Secretions (sIgA) Dimer (11S) J chain Secretory component Secretory Piece J Chain  IgA ˜ Structure ˜ Properties Ø 2nd highest serum Ig Ø Major secretory Ig (Mucosal or Local Immunity) Tears, saliva, gastric and pulmonary secretions Ø Does not fix complement (unless aggregated) Ø Binds to Fc receptors on some cells Antibody Structure—Secretory IgA Copyright ©2018, Elsevier Inc. All rights reserved. 63 Antibody Structure—IgD Copyright ©2018, Elsevier Inc. All rights reserved. 66  IgD ˜ Structure Ø Monomer Ø Tail piece Tail Piece  IgD ˜ Structure Ø Monomer Ø Tail piece Tail Piece Antibody Structure—IgE Copyright ©2018, Elsevier Inc. All rights reserved. 69  IgE ˜ Structure ˜ Properties Ø Least common serum Ig Binds to basophils and mast cells (Does not require Ag binding) Ø Allergic reactions Ø Parasitic infections (Helminths) Binds to Fc receptor on eosinophils Ø Does not fix complement  Human Immunoglobulin Light Chain Types ˜ Kappa (κ) ˜ Lambda (λ)  Human Immunoglobulin Light Chain Subtypes ˜ Lambda light chains Ø Lambda 1 (λ1) Ø Lambda 2 (λ2) Ø Lambda 3 (λ3) Ø Lambda 4 (λ4)  Immunoglobulins ˜ Nomenclature Ø IgM (kappa) Ø IgA1(lambda 2) Ø IgG ˜ Heterogeneity Immunoglobulin Classes (Cont.) Copyright ©2018, Elsevier Inc. All rights reserved. 82 Immunoglobulin Classes (Cont.) Copyright ©2018, Elsevier Inc. All rights reserved. 83  Structure of the Variable Region ˜ Hypervariable (HVR) or complimentarity determining regions (CDR) HVR3 150 Variability Index 100 HVR2 HVR1 50 FR1 FR2 FR3 FR4 0 25 50 75 100 Amino acid residue Framework regions  Immunoglobulin Variants ˜ Isotype determinants ˜ Allotype determinants ˜ Idiotype determinants Copyright ©2018, Elsevier Inc. All rights reserved. 85 Immunoglobulin Variants (Cont.) Copyright ©2018, Elsevier Inc. All rights reserved. 86 Immunoglobulin Variants (Cont.) Copyright ©2018, Elsevier Inc. All rights reserved. 87  Antibody Synthesis ˜ Primary antibody response ˜ Secondary (anamnestic) antibody response Copyright ©2018, Elsevier Inc. All rights reserved. 88 Antibody Synthesis (Cont.) Copyright ©2018, Elsevier Inc. All rights reserved. 89  Antibody Specificity and Diversity ˜ Based on clonal selection and Ig genetics ˜ 1950s: Jerne and Burnet’s theory of clonal selection for antibody formation: Lymphocytes are genetically preprogrammed to produce one type of immunoglobulin. A specific antigen finds the particular cells capable of responding to it, causing them to proliferate. Would require a large number of genes.  Antibody Specificity and Diversity (continued) ˜ 1965: Dryer and Bennett: Constant and variable portions of immunoglobulin chains are coded for by separate genes. ˜ 1987: Susumu Tonegawa: Specific Ig gene segments are selected and joined together during B-cell maturation.  Clonal Selection ˜ Each B cell has a BCR specific for a particular antigen. ˜ When antigen enters the body, it binds only to the B cells that possess BCRs specific for it. ˜ Only those B cells proliferate and differentiate into antibody-producing plasma cells. Monoclonal Antibodies Copyright ©2018, Elsevier Inc. All rights reserved. 93  Multiple Myeloma (MM) § Plasma Cell Cancer § Multiple bone lesions § Cause: Unknown, but could be radiation, obesity,… § Overproduction of a single Ig component called M Protein or paraprotein=Monoclonal gammopathies § M proteins in palsma and/or urine  Multiple Myeloma: Diagnostic Evaluation § Bleeding is common. § Platelet abnormalities are present. § Electrophoresis of serum or urine reveals tall sharp peaks on a densitometer tracing; a dense localized band is seen in 75% of myeloma cases. § A monoclonal serum protein is detected in 91% of MM patients. The type of antibody is IgG in most patients. IgA is seen less frequently, and IgD is rarely demonstrated. Bence Jones protein in urine: monoclonal light chains in the urine of patients with MM  Quantification of Antibodies § Provide information about the functional immune status of an individual § IgG, IgM and IgA van be quatified using : 1- Radial immunodiffusion 2- Nephelometry 3- Tubidimetry