Immunoglobulin - PDF

# Immunoglobulin - **Dr. Bilal Aheed** ## Objectives - Immune System - What is Antibodies - Types of immunoglobulin - Its structure of individual immunoglobulin - Role in human tissue or body - Function of immunoglobulin - Antigen Determination ## The Immune System - The latin term "IMMUNIS" m...

# Immunoglobulin - **Dr. Bilal Aheed** ## Objectives - Immune System - What is Antibodies - Types of immunoglobulin - Its structure of individual immunoglobulin - Role in human tissue or body - Function of immunoglobulin - Antigen Determination ## The Immune System - The latin term "IMMUNIS" means EXEMPT, referring to protection against foreign agents. - **Definition:** The integrated body system of organs, tissues, cells and cell products that differentiates self from non-self and neutralizes potentially pathogenic organisms. - (The American Heritage Stedman's Medical Dictionary) - **The Immune System Consists of:** - **1. Innate Immunity** - Primary Response - **2. Acquired Immunity** - Secondary Response ## Cells of the Immune System - **Diagram:** A diagram shows the various cells of the immune system and their relation to each other. - **Pluripotent Stem Cell** - Myeloid Stem Cell - Lymphoid Stem Cell - **Myeloid Stem Cell** - Erythrocyte - Megakaryocyte (blood clotting) - Monocyte - Macrophage - Granulocytes - **Lymphoid Stem Cell** - **Thymus** - T Lymphocyte, NK Lymphocyte - B Lymphocyte - Plasma Cell ## Immunoglobulin (Ig)/Antibody(Ab) - Gamma globulins called immunoglobulins (Ig) - Molecular weights between 160,000 and 970,000 - About 20% of all the plasma proteins - Composed of light and heavy polypeptide chains - Most are combinations of two light and two heavy chains ## Differences Between Antigen and Antibody - **Diagram:** A diagram shows an antigen (a bacterial cell) with epitopes on the cell surface. Antibodies are shown binding to the epitopes. - Antibodies, also called immunoglobulins, Y-shaped molecules are proteins manufactured by the body that help fight against foreign substances called **antigens**. - **Antigens** are any substance that stimulate the immune system to produce antibodies. - **Antigens** can be bacteria, viruses, or fungi that cause infection and disease. ## Antibodies vs Immunoglobulin - Antibodies are specific glycoprotein configurations produced by B-lymphocytes and plasma cells in response to a specific antigen and capable of reacting with that antigen - All antibodies are immunoglobulins, although not all Igs can function as antibodies. - The main difference between immunoglobulin and antibody is that immunoglobulin has a transmembrane domain in order to be attached to the plasma membrane whereas antibody does not have a transmembrane domain. ## Structure of Antibody/Immunoglobulin - **Fc Region:** Activate immune system - **Fab Region:** Antibodies binding sites - **Variable Region:** Unique for each antibody - **Constant Region:** Constant for all antibodies - **Epitopes:** Antigen determinant. - **Heavy Chain:** Classify the immunoglobulin - **Light Chain:** Kappa and Lambda - **Diagram:** A diagram shows the structure of an antibody with its different domains labeled: - **Antigen** - **CDRs** - **VH** - **VL** - **Light Chain (LC)** - **CL** - **Heavy Chain (HC)** - **CH1** - **Fc Region** - **CH2** - **CH3** - **Disulfide Bond** - **Antigen Binding Site** - **Fab Region** - **Hinge Region** - **Monomer:** A flexible Y-shaped molecule with four protein chains: - 2 identical light chains Kappa, or lambda - 2 identical heavy chains alpha, gamma, mu, delta or epsilon - **The Fragment Crystallizable Region (Fc Region)** is the tail region of an antibody that interacts with cell surface receptors called Fc receptors and some proteins of the complement system. - This property allows antibodies to activate the immune system. - **The other part of an antibody, called the Fab Region,** contains variable sections that define the specific target that the antibody can bind. - **Diagram:** A diagram shows an antibody bound to an Fc receptor on the surface of an effector cell. - **Pathogen:** A pathogen (e.g. a virus) is also shown bound to an antibody. ## Variable and Constant Region - **4. Two Regions:** - **Variable (V) Region:** The sequence of the ~110 N terminal residues of L chain and H chain was seen to be unique for each antibody with different binding specificity. - **N-end:** - L chain 1/2-VL - H chain 1/4-VH - **Constant (C) Region:** The C terminal sequence (~ 110 residues of L chain and remaining of H chain) was constant for all antibodies - **C-end:** - L chain 1/2-CL - H chain 3/4-CH - **Diagram:** A diagram shows the variable region and constant region of an antibody. ## Variable Region - **Diagram:** A diagram shows an antibody with its variable domains (VL and VH), constant domains (CL, CH1-CH3), and the hinge region highlighted. - **The amino acids of V region varies greatly among antibodies with different antigen specificity.** - **Hypervariable Regions/Complementarity-Determining Regions (CDRs) form the antigen-binding site.** ## Constant Region - **Diagram:** A diagram shows an antibody with its constant region, variable region, hinge region, and other domains. - **Regions of relatively constant sequence beyond the V regions.** - **The Ig constant region domains take part in various biological functions that are determined by the amino acid sequence of each domain.** ## Light and Heavy Chains - **Light Chain:** V_L (110 aa) + C_L (110 aa) - **Heavy Chain:** V_H (110 aa) + C_H1-C_H3 (or C_H4) (330-440 aa) - **Diagram:** A diagram shows the light chain and heavy chains of an antibody. - The chains are connected by disulfide bonds. - The variable and constant regions are labeled. ## Antigenic Determinant or Epitope - **The structure recognized by an antibody.** - **Diagram:** A series of diagrams shows an antibody binding to different epitopes on different antigens. - The binding site formed by the complementarity-determining regions is highlighted. - **Concept:** Epitopes can bind in pockets or grooves or on extended surfaces in the binding site of antibodies. ## Functions of the Domains on Ig - **Diagram:** A diagram shows the different regions of an antibody and their functions. - **Ag Binding** - **Binding to Fc Receptors** - **Complement Binding Site** - **Placental Transfer** ## The Class and Subclass of Immunoglobulin - In humans, there are five distinct classes of antibody/immunoglobulin molecule according to the sequence of constant region of H chain. - **H Chain:** - μ, γ, α, δ, ε - **The H chain of a given antibody molecule determines the class of that antibody.** - **Ig:** - IgM - IgG - IgA - IgD - IgE ## Heavy Chain - Minor differences in the amino acid sequences and differences in position and numbers of disulfide bond of the α and γ heavy chains led to further classification of the heavy chains that determine the subclass of antibody molecule they constitute. - **α Heavy Chains:** - α₁ - IgA₁ - α₂ - IgA₂ - **γ Heavy Chains:** - γ₁ - IgG₁ - γ₂ - IgG₂ - γ₃ - IgG₃ - γ₄ - IgG₄ - **Diagram:** A diagram shows the different subclasses of IgG with their disulfide bonds. ## 2 Light Chain Types: κ or λ - In humans, 60% of light chains are kappa and 40% are lambda; in mice 95% are kappa and 5% are lambda. - Comparison of λ chain sequences revealed minor differences that could be used to classify λ chains into subtypes - 3 in mice and 4 in humans. - Each antibody has two identical heavy and light chains. - A normal antibody molecule contains only one light-chain type, either κ or λ, never both. ## Hinge Region - **Diagram:** A diagram shows an antibody with its hinge region highlighted. - **The γ, δ, and α heavy chains contain an extended peptide sequence between the CH1 and CH2 domains that has no homology with the other domains.** - **IgG, IgD and IgA are rich in proline residues.** - **This gives IgG, IgD, and IgA segmental flexibility.** ## Function of Antibodies - 1. To neutralize toxins and viruses - 2. To opsonize microbes so they are more easily phagocytosed - 3. To activate complement - 4. To prevent the attachment of microbes to mucosal surfaces ## Function of Antibodies: Detailed Explanation - **Neutralization:** - **Diagram:** A diagram shows an antibody binding to a virus and preventing it from infecting a cell. - Antibodies bind to and inactivate viruses and toxins. - These antibodies are called “neutralizing antibodies.” - **Complement Recruitment by Antibodies:** - **Diagram:** A diagram shows an antibody binding to a bacterial cell and activating the complement system. - Antigen-antibody complexes activate the complement system (the classical pathway), triggering its antibacterial activity. - **Opsonization:** - **Diagram:** A diagram shows an antibody bound to a bacterial cell, which is being phagocytosed by a phagocytic cell. - Phagocytic cells grab the antibodies bound to the surface of foreign substances, for efficient phagocytosis. - **They are ready to eat.** ## Immunoglobulin (Ig) - **Diagram:** A diagram showing the five classes of immunoglobulin (IgA, IgG, IgM, IgE, IgD) with their corresponding heavy chains. - **1. IgG: γ heavy chains** - **2. IgA: α heavy chains dimer** - **3. IgM: μ heavy chains pentamer** - **4. IgE: ε heavy chains** - **5. IgD: δ heavy chains** ## Classes (Isotypes) of Immunoglobulins - **Classes based on constant region of heavy chains:** - Immunoglobulin A (IgA) - Immunoglobulin D (IgD) - Immunoglobulin E (IgE) - Immunoglobulin G (IgG) - Immunoglobulin M (IgM) - **Diagram:** A diagram shows the constant regions of an antibody. - **Differentiation of heavy chains:** - Length of C region, location of disulfide bonds, hinge region, distribution of carbohydrate - **Classes have different effector functions.** ## Immunoglobulin - **Diagram:** A diagram shows the five classes of immunoglobulin (IgG, IgE, IgD, IgM, and IgA). ## Immunoglobulin G (IgG) - **Structure:** Monomer - **Percentage serum antibodies:** 80% - **Location:** Blood, lymph, intestine - **Half-life in serum:** 23 days - **Complement Fixation:** Yes - **Placental Transfer:** Yes - **Function:** 2nd Immune Response - **Known Functions:** Enhances phagocytosis, neutralizes toxins and viruses, protects fetus and newborn, complement activation - **Increases in:** - Chronic granulomatous infections - Infections of all types - Hyperimmunization - Liver disease - Malnutrition (severe) - Dysproteinemia - Disease associated with hypersensitivity granulomas, dermatologic disorders, and IgG myeloma - Rheumatoid arthritis - **Decreases in:** - Agammaglobulinemia - Lymphoid aplasia - Selective IgG, IgA deficiency - IgA myeloma - Bence Jones proteinemia - Chronic lymphoblastic leukemia ## IgA - **Diagram:** A diagram shows the structure of IgA in serum (monomer) and in secretions (dimer with J chain and secretory component). - The J chain and secretory component are highlighted. - **Structure:** - Serum: monomer - Secretions (sIgA) - Dimer (11S) - J chain - Secretory component ## Immunoglobulin A (IgA) - **Structure:** Monomer, Dimer and Secretory - **Percentage serum antibodies: 10-15%** - **Location:** Secretions (tears, saliva, colostrum, genitourinary tract, GIT, prostate, respiratory epithelium (bronchial tract), milk), blood and lymph. - **Half-life in serum:** 6 days - **Role:** Mucosal Immunity - **Complement Fixation:** No - **Placental Transfer:** No - **Known Functions:** Localized protection of mucosal surfaces. - Provides immunity to infant digestive tract. - **Increases (in adults) in:** - Waldenström's macroglobulinemia - Trypanosomiasis - Actinomycosis - Carrión's disease (bartonellosis) - Malaria - Infectious mononucleosis - Lupus erythematosus - Rheumatoid arthritis - Dysgammaglobulinemia (certain cases) - **Decreases in:** - Agammaglobulinemia - Lymphoproliferative disorders (certain cases) - Lymphoid aplasia - IgG, and IgA myeloma - Dysgammaglobulinemia - Chronic lymphoblastic leukemia ## Immunoglobulin M (IgM) - **Structure:** Pentamer and monomer (Largest Ab) - **Percentage serum antibodies:** 5-10% - **Location:** Blood, lymph, B cell surface (monomer) - **Half-life in serum:** 5 days - **Complement Fixation:** Yes - **Placental Transfer:** No - **Known Functions:** - First antibodies produced during an infection. - Effective against microbes and agglutinating antigens. - ONLY IgM can also produces from **fetus** (utero) and neonate/newborn (active immunity). ## IgE and IgD Antibodies of the Immune Response - **IgE** - Binds with high affinity to receptors on mast cells, basophils and activated eosinophils. - Longer half-life when cell bound. - Initiates a strong inflammatory reaction to parasites. - Involved in allergic reactions. - **Diagram:** A diagram shows the structure of IgE. - **Structure:** Monomer - **Extra domain (CH4)** -**IgD** - Antigen receptor on mature B-cells. - No other known function. - **Diagram:** A diagram shows the structure of IgD. - **Structure:** - Monomer - Tail piece ## Immunoglobulin E (IgE) - **Structure:** Monomer - **Percentage serum antibodies:** 0.002% - **Location:** Bound to mast cells and basophils throughout body. Blood. - **Half-life in serum:** 2 days. - **Complement Fixation:** No - **Placental Transfer:** No - **Known Functions:** - Allergic reactions. - Possibly lysis of worms. - It recognized cancer cell. - **Diagram:** A diagram shows the structure of IgE. - **Increases in:** - Atopic skin diseases such as eczema - Hay fever - Asthma - Anaphylactic shock - IgE-myeloma myeloma - **Decreases in:** - Congenital agammaglobulinemia - Hypogammaglobulinemia due to faulty metabolism or synthesis of immunoglobulins. ## Immunoglobulin D (IgD) - **Structure:** Monomer. - **Percentage serum antibodies:** 0.2% . - **Location:** B-cell surface, blood, and lymph. - **Half-life in serum:** 3 days. - **Complement Fixation:** No. - **Placental Transfer:** No. - **Known Functions:** - In serum function is unknown. - **It activates B-cells and defends body by immune system**. - **It activates to produce anti-microbial factor to participate in respiratory immune defense in human**. - **Increases in:** - Chronic infections - IgD myelomas ## Primary and Secondary Response - **Diagram:** A diagram showing the primary and secondary antibody response curves for IgG and IgM. ## Antigenic Determinants on Immunoglobulins - **3 Major Categories:** - **Isotypic determinants** - **Allotypic determinants** - **Idiotypic determinants** - **Diagram:** A series of diagrams showing the three major categories of antigenic determinants. ## Isotypic Determinants - **Diagram:** A diagram shows an antibody with its isotypic determinants marked. - **Definition:** Isotypes are antigenic determinants that characterize classes and subclasses of antibody. - **Location:** Isotypes are found in the constant region of the heavy chain and light. - **Occurrence:** Isotypes are found in ALL NORMAL individuals in the species. - **Different species inherit different constant-region genes and therefore express different isotypes.** - **When an antibody from one species is injected into another species, the isotypic determinants will be recognized as foreign, inducing an antibody response to the isotypic determinants on the foreign antibody.** - **Antibodies to isotypes are used for quantitation of Ig classes and subclasses in research or clinic.** ## Allotypic Determinants - **Diagram:** A diagram shows an antibody with its allotypic determinants marked. - **Definition:** Additional antigenic features of Ig that vary among individuals of the same species and are under genetic control. - **Location:** The allotypic differences are localized to the constant region of the heavy and light chains. - **Occurrence:** Individual allotypes are found in individual members of a species. Any individual Ig molecule will only have one allotype. - **Antibody to allotypic determinants can be produced by injecting antibodies from one member of a species into another member of the same species who carries different allotypic determinants.** - **Allotypes represent slight differences in the amino acid sequences in the heavy or light chains of different individuals.** ## Idiotypic Determinants - **Diagram:** A diagram shows an antibody with its idiotypic determinants marked. - **Definition:** Unique antigenic determinants present on individual antibody molecules or on molecules of identical specificity. - **Location:** Idiotypes are localized on the variable region of the Ig molecules. - **The unique amino acid sequence of the VH and VL domains of a given antibody can function not only as an antigen binding site but also as a set of antigenic determinants.** - **Each individual antigenic determinant of the variable region is refers to as an idiotype. - **Each antibody will present multiple idiotypes. - **Idiotypic determinants of the antibody can recognized by self immune system to generate anti-idiotype Abs.**