Antibodies
Antibodies are proteins produced by the immune system in response to the presence of foreign substances, such as bacteria or viruses. They recognize and bind to specific molecules, known as antigens, to help neutralize or eliminate the foreign invaders. This targeted response is a key component of the body's defense against infections and diseases.
7 Key excerpts on "Antibodies"
eBook - ePubImmunology
A Short Course
- Richard Coico(Author)
- 2021(Publication Date)
- Wiley-Blackwell(Publisher)
...6 ANTIBODY STRUCTURE, FUNCTION, AND INTERACTIONS WITH ANTIGEN INTRODUCTION One of the major functions of the immune system is the production of soluble proteins that circulate freely and exhibit properties that contribute specifically to immunity and protection against foreign material. These soluble proteins are the Antibodies, which belong to the class of proteins called globulins because of their globular structure. Initially, owing to their migratory properties in an electrophoretic field, they were called γ‐globulins (in relation to the more rapidly migrating albumin, α‐globulin, and β‐globulin); today they are known collectively as immunoglobulins (Igs). Immunoglobulins can be membrane bound or secreted. Membrane‐bound antibody is present on the surface of B cells where it serves as the antigen‐specific receptor. The membrane‐bound form of antibody is associated with a heterodimer called Igα/Igβ to form the B‐cell receptor (BCR). As will be discussed in Chapter 9, the Igα/Igβ heterodimer mediates the intracellular signaling mechanisms associated with B‐cell activation. Secreted Antibodies are produced by plasma cells—the terminally differentiated B cells that serve as antibody factories that reside largely within the bone marrow. The structure of immunoglobulins incorporates several features essential for their participation in the immune response. The two most important of these features are specificity and biological activity. Specificity is attributed to a defined region of the antibody molecule containing the hypervariable or complementarity‐determining region (CDR). This restricts the antibody to combine only with those substances that contain a particular antigenic structure. The existence of a vast array of potential antigenic determinants, also known as epitopes, prompted the evolution of a system for producing an enormous repertoire of antibody molecules, each of which is capable of combining with a particular antigenic structure...
eBook - ePub- Peter J. Delves, Seamus J. Martin, Dennis R. Burton, Ivan M. Roitt(Authors)
- 2016(Publication Date)
- Wiley-Blackwell(Publisher)
...CHAPTER 3 Antibodies Key topics The division of labor Five classes of immunoglobulin The IgG molecule The structure and function of the immunoglobulin classes Genetics of antibody diversity and function Just to recap … In order to resist the onslaught of a myriad of pathogens, we have evolved general mechanisms of defense (innate immunity) and mechanisms that are specific for a given pathogen (specific acquired or adaptive immunity). The latter mechanism, as its name implies, can be acquired and optimized through contact with the pathogen or through vaccination. The key players in specific immunity are Antibodies and T‐cells. In this chapter, we consider Antibodies in some detail. Introduction In essence, antibody molecules carry out two principal functions in immune defense. The first function is to recognize and bind to foreign material (antigen). This generally means binding to molecular structures on the surface of the foreign material (antigenic determinants) that differ from molecular structures made by the cells of the host. These antigenic determinants are usually expressed in multiple copies on the foreign material, such as proteins or carbohydrates on a bacterial cell surface or envelope spikes on the surface of a virus. Antibodies of a single host can recognize a huge variety of different molecular structures – a human is capable of producing Antibodies against billions of different molecular structures. This is described as antibody diversity and is necessary to respond to the huge diversity of molecular structures associated with (often highly mutable) pathogens. The simple act of antibody binding may be sufficient to inactivate a pathogen or render a toxin harmless. For instance, antibody coating of a virus can prevent entry into target cells and thereby “neutralize” the virus. However, in many instances, a second function of the antibody molecule is deployed to trigger the elimination of foreign material...
eBook - ePubBacterial Pathogenesis
A Molecular Approach
- Brenda A. Wilson, Malcolm Winkler, Brian T. Ho(Authors)
- 2019(Publication Date)
- ASM Press(Publisher)
...Humoral immunity involves activation of na ï ve B cells through one of two pathways. The first pathway is a T-cell-dependent process, which is followed by clonal expansion and proliferation of the activated mature B cells and their terminal differentiation into plasma cells (mature, nonproliferating B cells that act as professional antibody-producing factories). Alternatively, T-cell-independent activation of B cells can occur through direct binding of highly repetitive structures on their surfaces, which leads to proliferation, maturation, and production of Antibodies. Antibodies generated through this T-cell-independent pathway tend to have lower affinity for their targets than those generated through the T-cell-dependent activation of B cells. Antibodies are found in blood (serum) and tissue fluids, as well as many bodily secretions (e.g., saliva, mucosal fluids, vaginal fluids, and breast milk). Antibodies carry out a number of the adaptive immune system’s critical tasks, including: binding and neutralizing the activities of foreign substances, such as toxins, bacteria, and other pathogens; coating foreign substances for enhanced opsonization and clearance from the body; and targeting infected host cells for the killing action of cytotoxic T cells (CTLs) and natural killer (NK) cells. To understand how different Antibodies perform such diverse tasks, it is first necessary to understand how each type of antibody is put together and how they work. Characteristics of Antibodies and Their Diverse Roles in Preventing Infection The basic structures of the five types of Antibodies (IgG, IgM, IgD, IgE, and IgA/sIgA) are shown in Figure 4-1. The antibody monomer consists of a complex of two heavy chains (H-chains) and two light chains (L-chains). The words “heavy” and “light” refer to the size of the peptide chain, with the H-chain being the larger of the two. The H-chains and L-chains are held together by a combination of disulfide bonds and noncovalent interactions...
eBook - ePubBionanotechnology
Principles and Applications
- Anil Kumar Anal(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
...5 Immune Systems, Molecular Diagnostics, and Bionanotechnology 5.1 Introduction Emil von Behring, the father of immunology, and Shibasaburo Kitasato discovered a compound in blood that neutralized diphtheria toxin, which was later termed as Antikörper or Antibodies. Antibodies were observed to show toxin specificity, that is, the ability to distinguish between two immune components. The terms Antisomatogen and Immunkörperbildner were coined referring to the substance that caused the formation of antibody, which gave rise to the term antigen. Hence, antibody and its cognate antigen led to the foundation of immunology (Schroeder and Cavacini 2010). Innate immunity and adaptive immunity are the two types of human immune responses. Innate immunity system, including components such as epithelial cells, phagocytic cells, cytokines, natural killer cells, and complement system, is the early defense system for the development of adaptive immunity (Moulds 2009). Adaptive or humoral immunity shows immune response against foreign materials and pathogens via cell-mediated and antibody-mediated response mechanisms. In cell-mediated response, T-lymphocytes cells are activated to eliminate pathogens that exist within host cell and in antibody-mediated response and B-lymphocyte cells are activated to eliminate pathogens surviving outside the host cells (Moticka 2016). 5.2 Antibodies Antibodies, also known as immunoglobulins (Ig), are glycoproteins produced by B-lymphocytes in response to antigens and foreign body particles (e.g., virus, bacteria, endoparasite, drugs, dust, and pollen grains). During adaptive immunity response, antigen-specific B-lymphocyte recognizes antigens with the help of antibody (B-cell receptor), which are activated with the assistance of helper T-lymphocytes (Th cell). The Th cells, in turn, are activated by antigen-presenting cells (APC) displaying a processed form of antigens...
eBook - ePub- Eleftherios P. Diamandis, Theodore K. Christopoulos, Eleftherios P. Diamandis, Theodore K. Christopoulos(Authors)
- 1996(Publication Date)
- Academic Press(Publisher)
...Furthermore, recent advances in molecular biology demonstrate the mechanism by which this unique structure provides the vast diversity required. Immunoglobulin molecules are bifunctional proteins having unique recognition sites which specifically bind antigen, as well as functional sites remote from the antigen binding site. The latter participate in various effector functions such as complement activation, stimulation of mast cells to release histamine, and removal of antigens in circulating immune complexes. In this way Antibodies participate in many different reactions which make up the immune response. The development of our understanding of immunoglobulin structure and function has been reviewed extensively(12 – 14). As a group, Antibodies are heterogeneous proteins which can be classified into a small number of classes and subclasses based on the presence of certain common antigenic determinants shared by the members of the group. Each subclass comprises individual populations of similar proteins with unique amino acid sequence, each one of which is the product of single B-cell clone. Heterogeneity within a class was first noted as variable electrophoretic mobility of the major classes of immunoglobulins. 2.2. Basic Structure The basic structural unit of all classes of immunoglobulins is a symmetric four-chain heterodimer made of two identical heavy chains (H, MW 50,000 Da each) and two identical light chains (L, MW 25,000 Da) which form the characteristic Y-shape (Fig. 2.1). Each L chain binds a H chain with one or more disulfide (–s–s–) bonds. The two H chains likewise are bound by one or more disulfide bonds in the “hinge” region, all of which contribute to the chemical stability of immunoglobulin molecules. Immunoglobulin heavy chains μ (IgM) and ε (IgE) do not have a hinge region, but contain additional amino acids in an additional constant domain in the general location of the hinge...
eBook - ePubThe Immune Response
Basic and Clinical Principles
- Tak W. Mak, Mary E. Saunders, Maya Rani Chaddah, Wendy Lynn Tamminen(Authors)
- 2005(Publication Date)
- Academic Press(Publisher)
...The presence in the host’s plasma of all of these different Antibodies specific for different regions of the same antigen makes a natural antiserum polyclonal —that is, containing Antibodies produced by many different B cell clones. Such antigen-specific Antibodies in a polyclonal antiserum preparation have a wide variety of amino acid sequences, but they all act against the same antigen. In addition, as the immune response progresses, Antibodies to a given epitope are produced, which have the same specificity, but which differ in isotype, providing a further layer of heterogeneity (see isotype switching later in this chapter and in Ch. 9). It was the polyclonal character of the natural antibody response to antigen, and the fact that a single type of antibody protein is present in only very small amounts, that made the initial sequencing of Antibodies such a challenge. In 1975, Georges Köhler and César Milstein developed the hybridoma technology, which allows scientists to create immortalized B cells secreting immense amounts of pure antibody of a single known specificity. Such Igs are known as monoclonal Antibodies (see Ch. 7). This groundbreaking technique, which garnered for its creators the Nobel Prize in Physiology or Medicine in 1984, has been used to great advantage in generating tools for both basic and industrial research and for clinical applications. Studies using monoclonal Antibodies, or mAbs, have greatly refined our knowledge of the function and structure of Ig molecules. B. The Structure of Immunoglobulins Immunoglobulins are specialized glycoproteins synthesized only by B lymphocytes. These proteins are encoded by a genetic locus whose almost unique features confer the unusual structural characteristics of the Ig polypeptide chains. Immunoglobulins are first expressed in a membrane-bound form on the surface of B cells, where they function as part of the B cell’s antigen receptor...
eBook - ePubIntroductory Immunology
Basic Concepts for Interdisciplinary Applications
- Jeffrey K. Actor(Author)
- 2019(Publication Date)
- Academic Press(Publisher)
...Orthologous lymphocytes in humans were determined to develop in the bone marrow. It is now understood that the B subset of lymphocytes is responsible for humoral immunity, defined by their expression of antibody molecules. Structural Characteristics of Immunoglobulins Immunogloblulins, interchangeably referred to as Antibodies, share a common structure that allows them to bind to a nearly limitless number of specific antigens (including proteins, carbohydrates, glycoproteins, polysaccharides, nucleic acids, and lipids). Their structure confers multiple cellular processes, mediated by variable and constant region domains. The anatomy of the immunoglobulin in its monomeric form may be described as a Y -shaped glycoprotein consisting of two identical heavy chains of 55 kDa, paired with two identical light chains of 25 kDa (Fig. 3.1). These chains are held together by one or more interchain disulfide bonds; enzymatic cleavage of the disulfide bonds results in two fragments—a homogenous portion that could be crystallized (fragment, crystalline; Fc) and another fragment that could bind antigen (Fab2). These regions denote the effector antigen-binding functions of the antibody molecule. Within the heavy chain at the junction of the Fab 2 and Fc regions are short amino acid sequences that are rich in proline and cysteine. These are hinge regions, which confer flexibility for optimized binding with antigen. Fig. 3.1 Anatomy of the immunoglobulin. The basic structure of the antibody contains heavy chains and light chains, showing intradisulfide and interdisulfide bonds and the characteristic hinge region. The interactions between variable domains constitute the antigen-binding domain, while the constant regions confer specific biological properties of the molecule. Each heavy chain pairs with one of two varieties of light chains, the kamma or lambda light chain, to comprise the Fab 2 portion of the antibody...
