Essentials of Clinical Immunology PDF 6th Edition

ESSENTIALS OF CLINICAL IMMUNOLOGY H E LEN C HAPEL, M AN SEL HAENEY SIRAJ MISBAH AND NEIL SNOWDEN 6TH EDITION Available on Learn Smart. Choose Smart.  Essentials of C...

ESSENTIALS OF CLINICAL IMMUNOLOGY H E LEN C HAPEL, M AN SEL HAENEY SIRAJ MISBAH AND NEIL SNOWDEN 6TH EDITION Available on Learn Smart. Choose Smart.  Essentials of Clinical Immunology Helen Chapel MA, MD, FRCP, FRCPath Consultant Immunologist, Reader Department of Clinical Immunology Nuffield Department of Medicine University of Oxford Mansel Haeney MSc, MB ChB, FRCP, FRCPath Consultant Immunologist, Clinical Sciences Building Hope Hospital, Salford Siraj Misbah MSc, FRCP, FRCPath Consultant Clinical Immunologist, Honorary Senior Clinical Lecturer in Immunology Department of Clinical Immunology and University of Oxford John Radcliffe Hospital, Oxford Neil Snowden MB, BChir, FRCP, FRCPath Consultant Rheumatologist and Clinical Immunologist North Manchester General Hospital, Delaunays Road Manchester Sixth Edition This edition first published 2014 © 2014 by John Wiley & Sons, Ltd Registered office: John Wiley & Sons, Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK Editorial offices: 9600 Garsington Road, Oxford, OX4 2DQ, UK      The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK      350 Main Street, Malden, MA 02148-5020, USA For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley. com/wiley-blackwell The right of the author to be identified as the author of this work has been asserted in accordance with the UK Copyright, Designs and Patents Act 1988. 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No warranty may be created or extended by any promotional statements for this work. Neither the publisher nor the author shall be liable for any damages arising herefrom. First published 1984 ELBS edition 1986 Second edition 1988 Third edition 1993 Fourth edition 1999 Fifth edition 2006 Sixth edition 2014 Library of Congress Cataloging-in-Publication Data Chapel, Helen, author. Essentials of clinical immunology / Helen Chapel, Mansel Haeney, Siraj Misbah, Neil Snowden. – Sixth edition.     p. ; cm. Preceded by: Essentials of clinical immunology / Helen Chapel... [et al.]. 5th ed. 2006. Includes bibliographical references and index. ISBN 978-1-118-47295-8 (pbk. : alk. paper) – ISBN 978-1-118-48784-6 – ISBN 978-1-118-48785-3 – ISBN 978-1-118-48786-0 (emobi) – ISBN 978-1-118-48787-7 (epub) – ISBN 978-1-118-48788-4 (epdf ) I. Haeney, Mansel, author. II. Misbah, Siraj A., author. III. Snowden, Neil, author. IV. Title. [DNLM: 1. Immunity–immunology. 2. Immune System Phenomena–physiology. QW 540] RC582 616.07'9–dc23       2013024794 A catalogue record for this book is available from the British Library. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Cover image: Tim Vernon / Science Photo Library Cover design by Visual Philosophy Set in 10/12 pt Adobe Garamond Pro by Toppan Best-set Premedia Limited 1 2014 Contents Preface to the Sixth Edition iv Preface to the First Edition v How to Use Your Textbook vi About the Companion Website ix Key to Illustrations x 1 Basic Components: Structure and Function 1 2 Infection 34 3 Immunodeficiency 54 4 Anaphylaxis and Allergy 86 5 Autoimmunity 105 6 Lymphoproliferative Disorders 121 7 Immune Manipulation 137 8 Transplantation 157 9 Kidney Diseases 171 10 Joints and Muscles 194 11 Skin Diseases 219 12 Eye Diseases 236 13 Chest Diseases 245 14 Gastrointestinal and Liver Diseases 263 15 Endocrinology and Diabetes 288 16 Non-Malignant Haematological Diseases 300 17 Neuroimmunology 312 18 Immunological Diseases in Pregnancy 324 19 Techniques in Clinical Immunology 332 Appendix: Further Resources 351 Index 353 Preface to the Sixth Edition This is the last edition of the book in this format and the first as a digital edition; some progress since the first edition in 1984. During this time there have been fantastic advances in basic immunology and clinical applications, so that many of the earlier concepts are outmoded, redundant or just wrong. Keeping up to date is an increasingly time consuming and difficult task, not least to keep pruning exciting new findings in basic immunology that do not yet add much to our overall understanding of the important role of the immune system in health and disease. Since the fifth edition in 2006, Mansel Haeney has finally retired completely and sadly could not be persuaded that his help would be invaluable (it would have been); I have missed the laughter generated over many years about ‘pompous text’ and ‘over-researched detail’. In addition, Neil Snowden has moved to full-time rheumatology and clinical administration and was not able to take part and Siraj Misbah has become Clinical Lead in Immunology and is active on any number of national and international com- mittees. So that left only one of the four, who is therefore responsible for all the mistakes in this edition. Blackwell Scientific – now Wiley-Blackwell – were very persuasive and hence assistance was found in the form of Tom Hills, a Rhodes scholar from New Zealand, formerly an MSc student on the Integrated Immunology course in Oxford and currently a DPhil student. Tom has read and updated all the clinical chapters with me, as well as providing enthusiasm and encouragement to complete the task. I am indebted to him. I am also grateful to Vojtech Thon, Associate Professor in Brno, who has not only translated this edition into the Czech language but checked the English version as he went along; a mammoth task that he has undertaken with great determination and precision. My grateful thanks to him too. This edition includes a rewrite of Chapter 1 since there is so much new information about Basic Immunology compared with only 6 years ago. The chapter on Pregnancy has been revised to include associated immunological diseases only, since the basic immunology of pregnancy is an area of specialised interest rather than mainstream Clinical Immunology. For the same reason, I have resisted adding a whole chapter on Tumour Immunology (though this can be found in the French edition for those who are really keen!), settling instead to expand the chapter on Immune Manipulation. For students who may read older texts, I have left in comments on some of the now outdated tests or therapies and, where I can, have provided explanations as to why they have been superseded, so that students are not misled. The biggest change in the clinical sections relates to the genetic insights provided by the many genome-wide associa- tion studies (GWAS) now undertaken for most immunological diseases. These studies have provided both new understanding and many ‘red herrings’. The rapid growth in primary immunodeficiencies and the discovery of the many new genes in various complex conditions have shown that many of the genes mutated in primary immunodeficiencies are multifunctional; furthermore, some are involved in several important/central pathways whilst others are redundant. It has been difficult to choose those that are important to students of Clinical Immunology and I have included only a small selection of examples. As before, the bold type in the text indicates the content of each paragraph; really important points are identified by italics. Since several student reviews, while generous in their comments, requested more MCQs for each section, these are on the website, with answers as before: www.immunologyclinic.com. My thanks for help with particular chapters go to Beth Psaila (also my daughter-in-law), who rewrote much of the lymphoproliferation chapter, Georg Hollander, who kept me straight on autoimmunity and tolerance as well as new basic concepts, Meilyn Hew for reading the practical chapter and Siraj Misbah for making sure that my rheumatology was up to date. This edition would not have happened without Martin Davies at Wiley-Blackwell, who talked me into it, and Karen Moore, who edited the final revised version. I thank them for their persistence and help in achieving a final edition. Finally, I thank my family once again – and, I promise, for the last time. They have been most long- suffering, allowing ‘the seeming endless intrusion of Clinical Immunology into their lives’ – as Mansel wrote for the first edition in 1984. Helen Chapel Preface to the First Edition Immunology is now a well-developed basic science and much is known of the normal physiology of the immune system in both mice and men. The application of this knowledge to human pathology has lagged behind research, and immunologists are often accused of practising a science which has little relevance to clinical medicine. It is hoped that this book will point out to both medical students and practising clini- cians that clinical immunology is a subject which is useful for the diagnosis and management of a great number and variety of human disease. We have written this book from a clinical point of view. Diseases are discussed by organ involvement, and illustrative case histories are used to show the usefulness (or otherwise) of immunological investiga- tions in the management of these patients. While practising clinicians may find the case histories irksome, we hope they will find the application of immunology illuminating and interesting. The student should gain some perspective of clinical immunology from the case histories, which are selected for their relevance to the topic we are discussing, as this is not a textbook of general medicine. We have pointed out those cases in which the disease presented in an unusual way. Those who have forgotten, or who need some revision of, basic immunological ideas will find them condensed in Chapter 1. This chapter is not intended to supplant longer texts of basic immunology but merely to provide a springboard for chapters which follow. Professor Andrew McMichael kindly contrib- uted to this chapter and ensured that it was up-to-date. It is important that people who use and request immunological tests should have some idea of their complexity, sensitivity, reliability and expense. Students who are unfamiliar with immunological methods will find that Chapter 17 describes the techniques involved. Helen Chapel Mansel Haeney 1984 vi / How to Use Your Textbook How to Use Your Textbook Features contained within your textbook Every chapter begins with a list of key topics contained within Key topics the chapter and an introduction to the chapter. 1.1 Introduction 2 1.2 Key molecules 2 4.1 Introduction 1.2.1 Molecules recognized by immune systems 4 ‘Allergy’ is a much-misunderstood term that is used wrongly in general parlance. Unfortunately, the term is often 1.2.2 Recognition molecules 4 used loosely to describe any intolerance of environmental factors irrespective of any objective evidence of immunological reactivity to an identified antigen. In this chapter, we distinguish those conditions in which 1.2.3 Accessory molecules 10 immunological reactivity to key antigens is well defined from the rest, since such patients often present to an allergy 1.2.4 Effector molecules for immunity 11 clinic because of a popular public perception that they are ‘allergic’ in origin. In order to avoid any confusion the relationship of these terms is shown in Box 4.1. 1.2.5 Receptors for effector functions 13 Case studies and other boxes give further insight into topics. Case 6.1 Acute leukaemia (common type) A 7-year-old boy presented with malaise and lethargy of 6 days duration. He had become inattentive at school, anorexic and had lost 3 kg in weight. On examination he was thin, anxious and clinically anaemic. There was mild, bilateral, cervical lymphadenopathy and moderate splenomegaly. On investigation, he was pancytopenic with a low haemoglobin (80 g/l), platelet count (30 109/l) and white cell count (1.2 109/l). The blood film showed that most leucocytes were blasts; the red cells were normochromic and normocytic. Bone marrow examination showed an overgrowth of primitive white cells with diminished numbers of normal erythroid and myeloid precursors. Acute leukaemia was diagnosed. Your textbook is full of photographs, illustrations and tables. 22 / Chapter 1: Basic Components: Structure and Function Chapter 1: Basic Components: Structure and Function / 23 active. C3b is then able to use factors D and B of the alterna- Classical pathway MBL Alternate pathway tive pathway to produce the active enzyme ‘C3bBb’. This latter Box 1.5 Physiological control of Phagocytic Opsonin Phagocytosis cell Antigen-antibody Bound Endotoxin; bacterial substance has two properties. It can break down more C3, complement complexes to surface cell walls None Feeble providing still more C3b; this is known as the ‘positive feed- 1 A number of the activated components are inherently Antigen alone carbohydrates C3 on pathogens C3 back loop’ of the alternative pathway (Fig. 1.19). Alternatively, unstable; if the next protein in the pathway is not Fc (IgG) C3bBb becomes stabilized in the presence of properdin to form immediately available, the active substance decays. receptor IgG Slow C3b C3b the C5 convertase of the alternative pathway. 2 There are a number of specific inhibitors, e.g. (FcRIII) Antigen + antibody (IgG) There are thus two ways of producing C5 convertase. In C1 esterase inhibitor, C3b the classical pathway, C5 convertase is made up of C3b, C4b factor I receptor C3b Better C5 convertase and C2b, while in the alternative pathway it is produced by factor H. (CRI) Antigen + antibody C3b, Bb and properdin (Fig. 1.19). 3 There are proteins on cell membranes that block the (IgM/IgG) + complement C5 C5b The third pathway of complement activation is initiated action of complement by mannan-binding lectin, MBL (also known as mannan- iC3b By increasing the rate of breakdown of activated receptor IgG, C3b Excellent Final lytic pathway binding protein), a surface receptor (see Fig. 1.19) shed into complement components e.g. DAF (CD55), MCP (CR3) Immune complex + C and iC3b the circulation, binding avidly to carbohydrates on the surface (CD46) of microorganisms. MBL is a member of the collectin family By binding C5b678 and preventing C9 from binding Fig. 1.21 Complement pathways and their initiating factors. of C-type lectins, which also includes pulmonary surfactant and polymerizing e.g. CD59. Fig. 1.22 Opsonins and the relationship to phagocytosis. MBL, Mannan-binding lectin. proteins, A and D. MBL is structurally related to C1q and activates complement through a serine protease known as MASP (MBL-associated serine protease), similar to C1r and collagen-like protein composed of six subunits, resembling a C1s of the classical pathway. Inherited deficiency of MASP-2 ‘bunch of tulips’ when seen under the electron microscope. has been shown to predispose to recurrent pneumococcal infec- C1q reacts with Fc via its globular heads; attachment by two tions and immune complex disease. Production of IFN-α, IFN-β, IL-12 critically spaced binding sites is needed for activation. The Fc All pathways converge on a common final lytic pathway regions of pentameric IgM are so spaced that one IgM mole- (‘attack’ sequence) of complement involving the sequential by cells bearing low-affinity FcγRIII receptors (NK cells T cell mediated killing cule can activate C1q; in contrast, IgG is relatively inefficient attachment of the components C5, C6, C7, C8 and C9 and (CD16+), monocytes, neutrophils) (see section 1.2.4) (Fig. because the chance of two randomly sited IgG molecules being resulting in lysis of the target cell such as an invading organism 1.22), without involvement of the MHC. Clustering of several Virus titre the critical distance apart to activate C1q is relatively low. IgA, or a virally infected cell. The lytic pathway complex binds to IgG molecules is required to trigger these low-affinity receptors IgD and IgE do not activate the classical pathway. the cell membrane and a transmembrane channel is formed. to bind, resulting in secretion of IFN-γ and discharge of gran- Once C1q is activated, C1r and C1s are sequentially This can be seen by electron microscopy as a hollow, thin- ules containing perforin and granzymes, as found in CTLs. NK mediated bound to generate enzyme activity (C1 esterase) for C4 and walled cylinder through which salts and water flow, leading to The overall importance of ADCC in host defence is unclear, killing C2 (see Fig. 1.19), splitting both molecules into “a” and “b” the uptake of water by a cell, swelling and destruction. During but it represents an additional mechanism by which bacteria 0 5 10 fragments. The complex C 4b2b is the classical pathway C3 the final lytic pathway, complement fragments are broken off. and viruses can be eliminated. Time (days) convertase. Other fragments released are C4a, C2a and a C5a and the activated complex C567 are both potent media- vasoactive peptide released from C2. C 4b2b cleaves C3 into tors of inflammation. C5a, along with C3a, are anaphylotox- 1.3.7 Natural killer cells Fig. 1.23 Role of cells in early immune response to virus two fragments, C3a possessing anaphylotoxic and chemotactic ins, i.e. cause histamine release from mast cells with a resulting NK cells look like large granular lymphocytes and are found infection. Early – innate immune cells produce type-I interferons activity and C3b that binds to the initiating complex and pro- increase in vascular permeability. C5a also has the property of in blood, liver and secondary lymphoid organs particularly the and IL-12, NK cells = natural killer cells; late – T cell mediated motes many of the biological properties of complement. The being able to attract neutrophils to the site of complement spleen and mucosal associated lymphoid tissue (MALT). They killing by antigen specific cells – cytotoxic T cells (CTL). C 4b2b3b complex so generated is an enzyme, C5 convertase, activation (i.e. it is chemotactic) (see Fig. 1.19). can kill target cells, even in the absence of antibody or anti- which initiates the final lytic pathway (the ‘attack’ sequence). The control of any cascade sequence is extremely impor- genic stimulation. The name ‘natural killer’ reflects the fact The alternative pathway is phylogenetically older than the tant, particularly when it results in the production of potentially that, unlike the adaptive system, they do not need prior activa- classical pathway. It is relatively inefficient in the tissues, and self-damaging mediators of inflammation. The complement tion but have the relevant recognition molecules on their sur- high concentrations of the various components are required. pathway is controlled by three mechanisms (see Box 1.5). faces already. Non-specific agents, such as mitogens, IFN-γ and killing The central reaction in this pathway, as in the classical one, is These mechanisms ensure that the potentially harmful IL-12, can activate them further. NK cells form an integral part NKR-P1(CD161) Carbohydrate the activation of C3, but the alternative pathway generates a effects of complement activation remain confined to the initi- of the early host response to viral infection (Fig. 1.23). The C3 convertase without the need for antibody, C1, C4 or C2. ating antigen without damaging autologous (host) cells. Table exact mechanisms by which NK cells distinguish between KIR MHC class I Instead, the most important activators are bacterial cell walls 1.9 lists some of the clinically important complement regula- infected and non-infected cells is not clear but is likely to inhibition and endotoxin (Fig. 1.21). tory proteins. When considering their role in pathology, there involve cell-surface receptors (Fig. 1.24). NK cells express two NK cell Target cell The initial cleavage of C3 in the alternative pathway are important caveats (see Box 1.5). types of surface receptor (see section 1.2.2). Expression of happens continuously and spontaneously (see Fig. 1.21), gen- MHC class I proteins by most normal cells prevents NK cells erating a low level of C3b. C3b is an unstable substance and, from killing healthy cells. Interference with this inhibition, by Fig. 1.24 Natural killer (NK) cell recognition of target cells. NK 1.3.6 Antibody-dependent cell-mediated cell killing is mediated by engagement of the receptor NKR-P1 if a suitable acceptor surface is not found, the attachment site virally induced down-regulation or alteration of MHC class I cytotoxicity with its carbohydrate ligand on the target cell. This is inhibited in C3b decays rapidly and the molecule becomes inactive. If, molecules, results in NK-mediated killing either directly (secre- however, an acceptor surface (bacterial cell walls and endo- by the interaction between the inhibitory receptor (KIR) and Antibody-dependent cell-mediated cytotoxicity (ADCC) is a tion of granzymes or perforin), by FcRIII and ADCC or by MHC class I on the target cell. toxin) is nearby, the C3b molecules can bind and remain mechanism by which antibody-coated target cells are destroyed secretion of IFN-γ and TNF-α. Table 1.5 Effector molecules in immunity Innate Adaptive Humoral Complement components for opsonization or lysis Specific antibodies for opsonization and phagocytosis or lysis with complement Cellular Perforin in NK cells creates pores in target cell membranes Perforin in cytolytic (CD8) T cells creates pores in specific target cell membranes, allowing entry of granzymes to cause apoptosis Granzymes in NK cells induce apoptosis in target cells NKT cells induce apoptosis by perforin production Lysosomes in phagocytic vacuoles result in death of ingested microbes Preformed histamine and related vasoactive substances as well as leukotrienes in mast cells This icon indicates that you can read more on a topic by visiting the companion website.  How to Use Your Textbook / vii The anytime, anywhere textbook Wiley E-Text For the first time, your textbook comes with free access to a Wiley E-Text: Powered by VitalSource version – a digital, interactive version of this textbook which you own as soon as you download it. 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Good luck with your studies! About the Companion Website Don’t forget to visit the companion website for this book: www.immunologyclinic.com There you will find valuable material designed to enhance your learning, including: Interactive multiple-choice questions Additional case studies and figures to test your knowledge Case studies from the book with additional figures for you to use for revision All figures from the book in PowerPoint format Useful website links Wiley E-Text access instructions A selection of review articles from the journal Clinical and Experimental Immunology Key to Illustrations Throughout the illustrations standard forms have been used for commonly-occurring cells and pathways. A key to these is given in the figure below. USER GUIDE Pre-B Pre-T B T Natural Plasma lymphocyte lymphocyte lymphocyte lymphocyte killer cell cell Macrophage Antigen-presenting cell Dendritic Mast cell Langerhans (APC) cell cell Basophil Eosinophil Neutrophil Monocyte Stem cell  1 CHAPTER 1 Basic Components: Structure and Function Key topics  1.1 Introduction 2  1.2 Key molecules 2  1.2.1 Molecules recognized by immune systems 4  1.2.2 Recognition molecules 4  1.2.3 Accessory molecules 10  1.2.4 Effector molecules for immunity 11  1.2.5 Receptors for effector functions 13  1.2.6 Adhesion molecules 15  1.3 Functional basis of innate responses 17  1.3.1 Endothelial cells 17  1.3.2 Neutrophil polymorphonuclear leucocytes 17  1.3.3 Macrophages 17  1.3.4 Dendritic cells 18  1.3.5 Complement 20  1.3.6 Antibody-dependent cell-mediated cytotoxicity 22  1.3.7 Natural killer cells 23  1.4 Functional basis of the adaptive immune responses 24  1.4.1 Antigen processing 24  1.4.2 T cell mediated activation responses 24  1.4.3 Antibody production 27  1.5 Physiological outcomes of immune responses 28  1.5.1 Killing of target cells (virally infected/tumour cells) 28  1.5.2 Direct functions of antibody 28  1.5.3 Indirect functions of antibody 28  1.5.4 Regulation 29  1.6 Tissue damage caused by the immune system 29  1.6.1 Inflammation: a brief overview 29  1.7 Organization of the immune system: an overview 30  1.8 Conclusions 33 Visit the companion website at www.immunologyclinic.com to download cases on these topics. Essentials of Clinical Immunology, Sixth Edition. Helen Chapel, Mansel Haeney, Siraj Misbah, and Neil Snowden. © 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd. 2 / Chapter 1: Basic Components: Structure and Function 1.1 Introduction The immune system evolved as a defence against infectious diseases. Individuals with markedly deficient immune responses, if untreated, succumb to infections in early life. There is, therefore, a selective evolutionary pressure for a really efficient immune system. Although innate systems are fast in response to pathogens, the evolution to adaptive responses provided greater efficiency. However a parallel evolution in pathogens means that all species, plants, insects, fish, birds and mammals, have continued to improve their defence mechanisms over millions of years, giving rise to some redundancies as well as resulting in apparent complexity. The aim of this chapter is to provide an initial description of the molecules involved, moving onto the role of each in the immune processes rather than the more traditional sequence of anatomical structure, cellular composition and then molecular components. It is hoped that this gives a sense of their relationship in terms of immediacy and dependency as well as the parallel evolution of the two immune systems. An immune response consists of five parts: 1. recognition of material recognized as foreign and dangerous; 2. an early innate (non-specific) response to this recognition; 3. a slower specific response to a particular antigen, known as adaptive responses; 4. non-specific augmentation of this response; 5. memory of specific immune responses, providing a quicker and larger response when that particular antigen is encountered the second time. Innate immunity, though phylogenetically older and important in terms of speed of a response, is less efficient. Humoral components (soluble molecules in the plasma) and cells in blood and tissues are involved. Such responses are normally accompanied by inflammation and occur within a few hours of stimulation (Table 1.1). Adaptive immune responses are also divided into humoral and cellular responses. Adaptive humoral responses result in the generation of antibodies reactive with a particular antigen. Antibodies are proteins with similar structures, known collectively as immunoglobulins (Ig). They can be transferred passively to another individual by injection of serum. In contrast, only cells can transfer cellular immunity. Good examples of cellular immune responses are the rejection of a graft by lymphoid cells as well as graft-versus-host disease, where viable transferred cells attack an immunologically compromised recipient that is unable to fight back. Antibody-producing lymphocytes, which are dependent on the bone marrow, are known as B cells. In response to antigen stimulation, B cells will mature to antibody-secreting plasma cells. Cellular immune responses are dependent on an intact thymus, so the lymphocytes responsible are known as thymus-dependent (T) cells. The developmental pathways of both cell types are fairly well established (Fig. 1.1). The recognition phase is common to both adaptive and innate immunity. It involves professional cells, known as classical dendritic cells, that recognize general pathogen features or specific antigenic molecules, process the antigens and present antigen fragments to the other cells of the immune systems as well as initiating non-specific inflammation to the pathogen. In the effector phase, neutrophils and macrophages (innate immunity) and antibodies and effector T lymphocytes (adaptive immunity) eliminate the antigen. In terms of disease, like other organs, the immune system may fail (immunodeficiency), may be come malignant (lymphoid malignancies) or produce aberrant responses (such as in autoimmunity or allergy). This chapter describes the normal immune system in order to lay the basis for discussing these ways in which it can go wrong and so cause disease. 1.2 Key molecules Antibodies are not only the surface receptors of B cells (BCRs) that recognize specific antigens, but, once the appropriate B Many types of molecules play vital roles in both phases of cells are activated and differentiate into plasma cells, antibodies immune responses; some are shared by both the innate and the are also secreted into blood and body fluids in large quantities adaptive systems. Antigens are substances that are recognized by to prevent that antigen from causing damage. T cells have immune components. Detection molecules on innate cells rec- structurally similar receptors for recognizing antigens, known ognize general patterns of ‘foreignness’ on non-mammalian as T-cell receptors (TCRs). Major histocompatibility complex cells, whereas those on adaptive cells are specific for a wide (MHC) molecules provide a means of self-recognition and also range of very particular molecules or fragments of molecules. play a fundamental role in T lymphocyte effector functions.  Chapter 1: Basic Components: Structure and Function / 3 Table 1.1 Components of innate and adaptive immunity Features Innate Adaptive Foreign molecules Structures shared by microbes, recognized Wide range of very particular molecules or fragments recognized as patterns (e.g. repeated glycoproteins) of molecules on all types of extrinsic and modified PAMPs self structures Nature of recognition Germline encoded – limited PRRs Somatic mutation results in wide range of specificities receptors and affinities Speed of response Immediate Time for cell movement and interaction between cell types Memory None Efficient Humoral components Complement components Antibodies Cellular components Dendritic cells, neutrophils, macrophages, Lymphocytes – T (Th1, Th2, Th17, T regs) B NK cells, NKT cells, B1 cells, epithelial cells, mast cells iNKT cells, γδ T cells Lymphocyte development Peripheral effector cells Myeloid cell Th1 Th Premyeloid Thymus T cell Th2 Pre-T Thymocyte Tc Self reactive cells Natural Pluripotential deleted T memory Killer cell stem cell Lymphocyte- committed Secretory B stem cell Bone marrow B Pre-B Plasma cell B memory Pre-monocyte Monocyte Macrophage Fig. 1.1 Development of different types of blood from a pluripotential stem cell in the bone marrow. The developmental pathway for natural killer (NK) cells is shown separately because it is thought NK cells may develop in both the thymus and the bone marrow. 4 / Chapter 1: Basic Components: Structure and Function Effector mechanisms are often dependent on messages from Table 1.2 Factors influencing the immune response to initiating or regulating cells; soluble mediators, which carry an antigen, i.e. its immunogenicity messages between cells, are known as interleukins, cytokines and chemokines. 1 Nature of molecule: Protein content Size 1.2.1 Molecules recognized by immune systems Solubility Foreign substances are recognized by both the innate and adap- 2 Dose: tive systems, but in different ways, using different receptors Low doses provoke small amounts of antibody with high (see section 1.2.2). The innate system is activated by ‘danger affinity and restricted specificity signals’, due to pattern recognition receptors (PRRs) on den- Moderate doses provoke large amounts of antibody but dritic cells recognizing conserved microbial structures directly, mixed affinity and broad specificity often repeated polysaccharide molecules, known as pathogen- High doses provoke tolerance associated molecular patterns (PAMPs). Toll-like receptors 3 Route of entry: (receptors which serve a similar function to toll receptors in ID, IM, SC→regional lymph nodes drosophila) make up a large family of non-antigen-specific IV→spleen receptors for a variety of individual bacterial, viral and fungal Oral→Peyer’s patches components such as DNA, lipoproteins and lipopolysaccha- Inhalation→bronchial lymphoid tissue rides. Activation of dendritic cells by binding to either of these 4 Addition of substances with synergistic effects, detection receptors leads to inflammation and subsequently acti- e.g. adjuvants, vation of the adaptive system. Phagocytic cells also recognize particular patterns associ- 5 Genetic factors of recipient animal: Species differences ated with potentially damaging materials, such as lipoproteins Individual differences and other charged molecules or peptides. Traditionally, antigens have been defined as molecules that ID, Intradermal injection; IM, intramuscular injection; IV, intravenous injection; SC, subcutaneous injection. interact with components of the adaptive system, i.e. T- and B-cell recognition receptors and antibody. An antigenic mole- cule may have several antigenic determinants (epitopes); each 1.2). Substances that improve an immune response to a sepa- epitope can bind with an individual antibody, and a single rate, often rather weak, antigen are known as adjuvants. The antigenic molecule can therefore provoke many antibody mol- use of adjuvants in humans, important in vaccines against ecules with different binding sites. Some low-molecular-weight infective agents and tumours, is discussed in section 7.3.2. molecules, called haptens, are unable to provoke an immune Superantigen is the name given to those foreign proteins response themselves, although they can react with existing which are not specifically recognized by the adaptive system antibodies. Such substances need to be coupled to a carrier but do activate large numbers of T cells regardless of specifi­­ molecule in order to have sufficient epitopes to be antigenic. city, via direct action with an invariant part of the TCR (see For some chemicals, such as drugs, the carrier may be a host section 2.4.2). (auto) protein. The tertiary structure, as well as the amino acid Self-antigens are not recognized by dendritic cells, so sequence, is important in determining antigenicity. Pure lipids inflammation and co-stimulation of T cells (see section 1.4.1) and nucleic acids are poor antigens, although they do activate is not induced. There are mechanisms to control any aberrant the innate system and can be inflammatory. adaptive responses to self-antigens, by prevention of produc- Antigens are conventionally divided into thymus-dependent tion of specific receptors and regulation of the response if the and thymus-independent antigens. Thymus-dependent anti- immune system is fooled into responding (see Chapter 5, gens require T-cell participation to provoke the production of Autoimmunity). antibodies; most proteins are examples. Thymus-independent antigens require no T-cell cooperation for antibody produc- 1.2.2 Recognition molecules tion; they directly stimulate specific B lymphocytes by virtue of their ability to cross-link antigen receptors on the B-cell There are several sets of detection molecules on dendritic cells surface, produce predominantly IgM and IgG2 antibodies and (Table 1.3): pattern recognition receptors (PRRs), such as Toll- provoke poor immunological memory. Such antigens include like receptors, as well as chemotactic receptors and phagocytic bacterial polysaccharides, found in bacterial cell walls. Endo- receptors. PRRs may be soluble or attached to cell membranes. toxin, another thymus-independent antigen, not only causes Mannan binding lectin is a protein that binds sugars on micro- specific B-cell activation and antibody production but also acts bial surfaces; if attached to a macrophage, it acts as a trigger as a stimulant for all B cells regardless of specificity. for phagocytosis and, if soluble, it activates the complement Factors other than the intrinsic properties of the antigen cascade resulting in opsonization. Others belonging to this can also influence the quality of the immune response (Table family are less well defined.  Chapter 1: Basic Components: Structure and Function / 5 Table 1.3 Markers on dendritic cells Immature dendritic cells Mature myeloid dendritic cells Function Antigen capture Antigen presentation to immature T cells for specific differentiation Co-stimulatory molecule expression, e.g. CD80, CD86 Absent or low ++ Adhesion molecules, e.g. ICAM-1 Absent or low ++ Cytokine receptors, e.g. IL-12R Absent or low ++ Pattern recognition receptors (PRRs), e.g. mannose ++ − receptor MHC class II: turnover Very rapid Persist >100 h density Reduced (approx. 1 × 106) Very high (approx. 7 × 106) ICAM-1, Intercellular adhesion molecule-1. Ligands Viruses Fig. 1.2 Sequential cellular events induced by engagement of Toll-like receptors on dendritic cells Lipopolysaccharide Gram-negative (LPS) bacteria neutrophils and macrophages by microbial ligands (TRAF, or or TNF receptor-associated factor; IKB, inhibitor kappa B; MAPK, mitogen-activated protein kinase; IRAK, interleukin-1 receptor-associated kinase). Toll-like receptors (TLRs) Myd 88 (adaptor protein) Family of IRAK enzymes Signalling pathways TRAF Inactivation Induction of of IKB MAPK kinases Outcomes Translocation of NFκB Pro-inflammatory cytokine secretion Activation of Activation of genes adaptive immunity in the nucleus Toll-like receptors (TLRs) are part of this family too. sion and the induction of pro-inflammatory cytokines (Fig. These are evolutionarily conserved proteins found on macro- 1.2). The clinical consequences of a defective TLR pathway are phages, dendritic cells and neutrophils. At least ten different discussed in section 3.4.1 (see Box 1.1 in this chapter also). TLRs are found in humans, each TLR recognizing a range of CD1 molecules are invariant proteins (MHC-like and particular motifs on pathogens, such as double-stranded RNA associated with β2-microglobulin – see later), which are present of viruses (TLR3), lipopolysaccharides of Gram-negative bacte- on dendritic and epithelial cells. CD1 combine with lipids, rial cell walls (TLR4), flagellin (TLR5) and bacterial DNA which are poor antigens and not usually well presented to the (TLR9), all highly conserved motifs unique to microorganisms. adaptive immune system, and so act as recognition molecules Upon binding to their ligands, TLRs induce signal transduc- for the intestine and other microbial rich surfaces. CD1 present tion, via a complex cascade of intracellular adaptor molecules lipids to the immune cells of the gut in particular, namely and kinases, culminating in the induction of nuclear factor non-MHC-restricted natural killer (NKT) cells and γδ T cells kappa B transcription factor (NFκB)-dependent gene expres- in the epithelium. 6 / Chapter 1: Basic Components: Structure and Function The genes for TCR chains are on different chromosomes: Box 1.1 Clinical consequences of a β and γ on chromosome 7 and α and δ on chromosome 14. defective Toll-like receptor pathway Each of the four chains is made up of a variable and a constant In humans, deficiency of IRAK-4 (interleukin-1 receptor- domain. The variable regions are numerous (although less so associated kinase) or MyDD88, key intracellular than immunoglobulin variable genes; they are joined by D molecules responsible for TLR signal transduction (Fig. and J region genes to the invariant (constant) gene by recom- 1.2) is associated with recurrent pyogenic bacterial binases, RAG1 and RAG2, the same enzymes used for making infections accompanied by failure to mount an antigen receptors on B cells (BCRs) and antibodies (section 1.4.1). appropriate acute-phase response (Case 3.6). The diversity of T-cell antigen receptors is achieved in a Mice lacking TLR4 are exceptionally susceptible to similar way for immunoglobulin, although TCRs are less diverse infection with Gram-negative bacteria since somatic mutation is not involved; perhaps the risk of ‘self recognition’ would be too great. The diversity of antigen binding is dependent on the large number of V genes and the way in which these may be combined with different D and J genes to provide different V domain genes. The similarities or chain or chain between TCRs and BCRs led to the suggestion that the genes evolved from the same parent gene and both are members of CD3 Variable a ‘supergene’ family. Unlike immunoglobulin, TCRs are not region secreted and are not independent effector molecules. A particular TCR complex recognizes a processed antigenic Constant region peptide in the context of MHC class I or II antigens (section 1.4.1) depending on the type of T cell; helper T cells recognize class II with antigen, and this process is enhance by the surface Plasma accessory protein CD4 (see later) and intracellular signals. membrane ZAP70 p56lck p59fyn Cytotoxic T cells (CTL/Tc) recognize antigens with class I (see section 1.3.1) and use CD8 accessory molecules for increased binding and signalling. Since the number of variable genes Fig. 1.3 Diagram of the structure of the T-cell receptor (TCR). available to TCRs is more limited, reactions with antigen The variable regions of the alpha (α) and beta (β) chains make might not be sufficient if it were not for the increased binding up the T idiotype, i.e. antigen/peptide binding region. The TCR is closely associated on the cell surface with the CD3 protein resulting from these accessory mechanisms. Recognition of that is essential for activation. processed antigen alone is not enough to activate T cells. Addi- tional signals, through soluble cytokines (interleukins), are needed; some of these are generated during ‘antigen processing’ (see Antigen processing, section 1.4.1). Antigenic epitopes, having been processed by dendritic Major histocompatibility complex molecules (MHC) cells, are recognized by cells of the adaptive system by means were originally known as ‘histocompatibility antigens’ because of specific receptors. Each T cell, like B cells, is pre-committed of the vigorous reactions they provoked during mismatched to a given epitope. It recognizes this by one of two types of organ transplantation. However, these molecules are known to TCRs, depending on the cell’s lineage and thus its effector play a fundamental role in immunity by presenting antigenic function. T cells have either αβTCR [a heterodimer of alpha peptides to T cells. Histocompatibility antigens in humans (α) and beta β) chains] or γδTCR [a heterodimer of gamma γ [known as human leucocyte antigens (HLA)] are synonymous and delta (δ) chains]. αβTCR cells predominate in adults, with the MHC molecules. MHC molecules are cell-surface although 10% of T cells in epithelial structures are of the glycoproteins of two basic types: class I and class II (Fig. 1.5). γδTCR type. In either case, TCRs are associated with several They exhibit extensive genetic polymorphism with multiple transmembrane proteins that make up the cluster differentia- alleles at each locus. As a result, genetic variability between tion 3 (CD3) molecule (Fig. 1.3), to make the CD3–TCR individuals is very great and most unrelated individuals possess complex responsible for taking the antigen recognition signal different MHC (HLA) molecules. This means that it is very inside the cell (signal transduction). Signal transduction difficult to obtain perfect HLA matches between unrelated requires a group of intracellular tyrosine kinases (designated persons for transplantation (see Chapter 8). The extensive p56 lck, p59 fyn, ZAP 70) to join with the cytosolic tails polymorphism in MHC molecules is best explained by the of the CD3–TCR complex and become phosphorylated. need of the immune system to cope with an ever-increasing Nearby accessory molecules, CD2, LFA-1, CD4 and CD8, range of pathogens adept at evading immune responses (see are responsible for increased adhesion (see section 1.2.6) but Chapter 2). are not actually involved in recognizing presented antigenic The TCR of an individual T cell will only recognize antigen fragments. as a complex of antigenic peptide and self-MHC (Fig. 1.4).  Chapter 1: Basic Components: Structure and Function / 7 APC APC APC Cell B C MHC MHC MHC membrane DR DQ type a type b type a DP A Ag Ag Ag P P Q Class III TCR TCR TCR Class II DQ Bf C4B Class I DP DR C2 C4A TNF B C A Centromere T cell T cell T cell RESPONDS NO RESPONSE NO RESPONSE (i) (ii) (iii) Chromosome 6 Fig. 1.4 MHC restriction of antigen recognition by T cells. T Fig. 1.6 Major histocompatibility complex on chromosome 6; cells specific for a particular peptide and a particular MHC allele class III antigens are complement components. TNF, Tumour will not respond if the same peptide were to be presented by a necrosis factor. different MHC molecule as in (ii) or as in (iii) if the T cell were to encounter a different peptide. APC, Antigen-presenting cell; TCR, T-cell receptor. Fig. 1.5) are made up of an α heavy chain, controlled by a gene in the relevant MHC locus, associated with a smaller chain called β2-microglobulin, controlled by a gene on chro- Peptide binding groove mosome 12. The differences between individual MHC class I antigens are due to variations in the α chains; the β2- α1 α2 α1 β1 microglobulin component is constant. The detailed structure of class I antigens was determined by X-ray crystallography. CHO CHO CHO This shows that small antigenic peptides (approx. nine amino CHO acids long) can be tightly bound to a groove produced by the β2m s s s s s s s s pairing of the two extracellular domains (α1 and α2) of the α chain. The affinity (tightness of binding) of individual peptide α3 α2 β2 binding depends on the nature and shape of the groove, and Plasma accounts for the MHC restriction mentioned earlier. membrane MHC class II antigens have two heavy chains, α and β, Class I Class II both coded for by genes in the MHC region of chromosome 6. The detailed structure of MHC class II antigens was also Fig. 1.5 Diagrammatic representation of MHC class I and class determined by X-ray crystallography. It has a folded structure II antigens. β2m, β2-microglobulin; CHO, carbohydrate side similar to class I antigens with the peptide-binding groove chain. found between the α and β chains (see Fig. 1.5). Whereas most nucleated cells express class I molecules, expression of class II molecules is restricted to a few cell types: dendritic cells, B lym- This process of dual recognition of peptide and MHC mol- phocytes, activated T cells, macrophages, inflamed vascular ecule is known as MHC restriction, since the MHC molecule endothelium and some epithelial cells. However, other cells restricts the ability of the T cell to recognize antigen (Fig. 1.4). (e.g. thyroid, pancreas, gut epithelium) can be induced to The importance of MHC restriction in the immune response express class II molecules under the influence of interferon was recognized by the award of the Nobel Prize in Medicine (IFN)-γ released during inflammation. In humans, there are to Peter Doherty and Rolf Zinkernagel, who found that virus- three groups of variable class II antigens: the loci are known as specific CTLs would only kill cells of the same particular allelic HLA-DP, HLA-DQ and HLA-DR. form of MHC molecule. In practical terms, there are different mechanisms by which MHC class I antigens are subdivided into three groups: antigens in different intracellular compartments can be cap- A, B and C. Each group is controlled by a different gene locus tured and presented to CD4+ or CD8+ T cells (Fig. 1.7). within the MHC region on chromosome 6 (Fig. 1.6) in Endogenous antigens (including viral antigens that have humans (different in mice). The products of the genes at all infected host cells) are processed by the endoplasmic reticulum three loci are chemically similar. All MHC class I antigens (see and presented by MHC class I-bearing cells exclusively to 8 / Chapter 1: Basic Components: Structure and Function CD8+ T cells. Prior to presentation on the cell surface, endog- The invariant chain also directs delivery of class II molecules enous antigens are broken down into short peptides, which are to the endosomal compartment where exogenous antigens then actively transported from the cytoplasm to endoplasmic are processed and made available for binding to class II reticulum by proteins. These proteins act as a shuttle and are molecules. so named ‘transporters associated with antigen processing’ The MHC class III region (see Fig. 1.6) contains genes (TAP-1 and TAP-2). TAP proteins (also coded in the MHC encoding proteins that are involved in the complement system class II region) deliver peptides to MHC class I molecules in (see section 1.4.1): the early components C4 and C2 of the the endoplasmic reticulum, from whence the complex of classical pathway and factor B of the alternative pathway. Some MHC and peptide is delivered to the cell surface. Mutations inflammatory proteins, e.g. tumour necrosis factor (TNF), are that affect function in either TAP gene prevent surface expres- also encoded in adjacent areas. Invariant MHC-like proteins, sion of MHC class I molecules. such as CD1 lipid-recognition receptors (see earlier), are not In contrast, exogenous antigens are processed by the lyso- coded for on chromosome 6, despite being associated with somal route and presented by MHC class II antigens to CD4+ β2-microglobulin. T cells (Fig. 1.7). As with MHC class I molecules, newly syn- In contrast to TCRs, the antigen receptors on B cells thesized MHC class II molecules are held in the endoplasmic (BCRs) are surface-bound immunoglobulin molecules that reticulum until they are ready to be transported to the cell can be secreted as soluble molecules. As with TCRs, they have surface. Whilst in the endoplasmic reticulum, class II mole- predetermined specificity for epitopes and are therefore cules are prevented from binding to peptides in the lumen by extremely diverse. The immune system has to be capable of rec- a protein known as MHC class II-associated invariant chain. ognizing all pathogens, past and future. Such diversity is pro- vided by the way in which all three types of molecules, TCR, BCR and antibody, are produced. The basic structure of the immunoglobulin molecule is Presentation of Presentation of shown in Fig. 1.8. It has a four-chain structure: two identical endogenous/viral antigens exogenous antigens by MHC class I molecules by MHC class II molecules heavy (H) chains (mol. wt. 50 kDa) and two identical light (L) chains (mol. wt. 25 kDa). Each chain is made up of domains of about 110 amino acids held together in a loop by a disulphide bond between two cysteine residues in the chain. Vesicle The domains have the same basic structure and many areas of similarity in their amino acid sequences. The heavy chains Golgi Class II mRNA determine the isotype of the immunoglobulin, resulting in endoplasmic Complex reticulum with MHC I Class I VH N mRNA terminal Endoplasmic Nucleus reticulum Vesicle Hinge region CH1 VL Viral antigen complexed CH3 CH2 with TAP S CL Viral C terminal S antigenic Viral peptide mRNA Endosome Viral DNA Fc VL Invariant chain is cleaved on fusion to enable class II molecules Viral DNA to bind antigen in the groove Fab VH Viral antigen/autoantigen Processed exogenous antigen MHC class I molecule MHC class II molecule TAP (transporters associated Invariant chain protects Fig. 1.8 Basic structure of an immunoglobulin molecule. with antigen processing) antigen binding groove Domains are held in shape by disulphide bonds, though only one is shown. C1–3, constant domain of a heavy chain; CL, constant domain of a light chain; VH, variable domain of a heavy Fig. 1.7 Different routes of antigen presentation, depending on chain; VL, variable domain of a light chain. =S=, disulphide nature of a