Concise Clinical Immunology for Healthcare Professionals

Mary Keogan, Eleanor M. Wallace, Paula O'Leary

• Publisher: Routledge
• Year: 2006
• ISBN:
  9781134428014
• Edition: 1
• Topic: Médecine
• Subtopic: Immunologie

This up-to-date immunology textbook provides a clear and simple introduction to clinical and laboratory immunology for health professionals in training or in practice. It covers:

• essential basic immunology
• clinical immunology
• laboratory investigations of immunological disorders
• treatments used in immunological disorders.

Focusing on clinical problems seen in practice and including self-assessment questions and case histories to aid learning and understanding, this is an invaluable resource for all medical students, nurses, nutritionists, pharmacists and physiotherapists.

PART 1
BASIC IMMUNOLOGY

INTRODUCTION

This part outlines basic aspects of how the immune system functions to protect us against pathogens. Some basic mechanisms underlying allergy and hypersensitivity are also included. The aim of this part is to provide a concise summary of essential aspects of immunity required to understand immunological diseases, investigations and treatment. There are many excellent textbooks available, which provide additional detail and more detailed explanation. We have, however, aimed to include sections describing clinically relevant aspects of basic immunology that are frequently scattered, such as ontogeny of the immune response, as well as sections aimed at integrating information.

REFERENCES

Davies, D. H., Halablab, M. A., Clarke, J., Fox, F. E. G. and Young, T. W. K. (1999) Infection and Immunity, London: Taylor & Francis.

Janeway, C. A., Travers, P., Hunt, S. and Walport, M. (2000) Immunobiology: The Immune System in Health and Disease, New York: Garland Publishing.

Nairn, R. and Helbert, M. (2002) Immunology for Medical Students, London: Mosby.

Parham, P. (2000) The Immune System, London: Elsevier Science.

KEY DEFINITIONS

Every effort has been made to explain new terms as this part progresses. However occasionally, particularly in the early chapters, fully explaining each term was too cumbersome. This list is not a complete glossary, merely a list of key definitions with which you should be familiar before reading this section.

Acute phase response (APR) Changes in metabolism occurring in response to inflammation, including inflammation caused by infection. The APR results in fever and changes in protein production. Production of transport proteins (such as albumin) is reduced, while production of protective proteins (immune system molecules, clotting factors and protease inhibitors) is increased. Proteins which increase during inflammation are known as acute phase reactants or acute phase proteins.

Antibody Immunoglobulin, secreted by plasma cells. Antibodies are key effectors in the humoral limb of the adaptive immune response. See Immunoglobulins.

Antigen Originally used to describe any molecule, which could lead to production of an antibody (antibody generators). The term antigen now includes any molecule which generates an adaptive immune response. Antigens which elicit hypersensitivity or allergic responses may be referred to as allergens.

Antigen presenting cell (APC) A cell capable of presenting antigen to a helper T cell. Competent antigen presentation requires expression of Major Histocompatability Complex (MHC) Class II as well as co-stimulatory molecules. Professional APCs are required to present antigen to naïve T cells, and antigen presentation is the cells primary function (e.g. dendritic cells). Non-professional APCs can present antigen to antigen experienced T cells, but have other functions in addition to antigen presentation (e.g. macrophages, B cells).

Chemokine A chemical messenger, the primary function of which is to control the movement of cells of the immune and haemopoietic systems.

Cytokine A chemical messenger which coordinates a function/functions of the immune system. Cytokines usually have highly localised effects. Cytokines may be divided into monokines (produced by monocytes/macrophages) or lymphokines (produced by lymphocytes).

Epitope The precise portion of an antigen which evokes an immune response. Antigens can contain many copies of the same epitope (common in carbohydrate antigens) or contain several different epitopes (common in protein antigens). B cells epitopes are conformational (i.e. affected by the three-dimensional structure of the antigen), while T cell epitopes are short peptides, not affected by antigen conformation.

Human leucocyte antigen (HLA) complex HLA is the human MHC. The term HLA may be used with reference to the chromosome region, the genes or protein molecules.

Immunoglobulins These are antigen-binding molecules produced by B cells. Immunoglobulins may be bound to the surface of the B cell, acting as an antigen receptor for the cell, or may be secreted, acting as the effector portion of the humoral response. Immunoglobulins (Ig) are divided into five functionally distinct major classes; IgG, IgA, IgM, IgD and IgE.

Interleukin (IL) A general term for cytokines produced by leucocytes.

Leukotriene Family of inflammatory mediators, produced by metabolism of arachidonic acid.

Lymphocytes Cells of the immune system, which are essential for all adaptive immune responses. Lymphocytes are subclassified as B lymphocytes (produce antibody response), T lymphocytes (produce cellular adaptive response) and Natural Killer or NK cells which usually form part of the innate immune response.

MHC Complex of genes which encode surface bound molecules which are involved in antigen presentation. The MHC molecules can be divided into Class I molecules, which are expressed on all nucleated cells and platelets, and MHC Class II molecules normally only expressed on specialised immune cells which present antigen to helper T cells. The human MHC is termed the HLA complex.

Monokines See under cytokines.

Opsonin A molecule which binds to pathogens or particles to make it more susceptible to phagocytosis. The process of coating particles to enhance phagocytosis is opsonisation. Opsonins include natural opsonins such as mannan binding lectin (MBL) and C-reactive protein, complement, as well as antibodies produced as part of the adaptive immune response.

Phagocyte A cell capable of ingesting a particle by phagocytosis, an active process involving formation of pseudopodia which engulf the particle. The vesicle so formed in the cell is called the phagosome. The principal phagocytes are neutrophils, monocytes and macrophages.

SECTION 1.1
Introduction

WHY DO WE NEED AN IMMUNE SYSTEM?

We encounter many thousands of microbes every day – many harmless, many beneficial but some that cause disease. The immune system defends us against infections caused by the huge variety of microorganisms we encounter, including viruses, bacteria, fungi and parasites. Microbes divide rapidly, each division allowing genetic variation and change. Thus microbes can change within days or even hours. It takes years for humans to reproduce and generate genomic variation. The immune system has developed elegant mechanisms that facilitate somatic change without genomic variation in response to infection and other stimuli.

THE MAJOR DEFENCE MECHANISMS AGAINST INFECTIONS

Microorganisms come in all shapes and sizes, with some penetrating into cells and others entering the body but remaining outside the cells. Thus the immune system has had to develop several different mechanisms to recognise and kill microbes depending on their characteristics. From the immune systems point of view, microbes can be divided according to type of infection caused.

Extracellular infection

• Bacteria enter tissues but usually remain outside the cells. However, as they are smaller than cells of the immune system, specialised immune cells can ingest, kill and digest the bacteria.
• Multi-cellular parasites also remain outside cells, however, as they are larger than immune cells, they cannot be ingested and so additional immune mechanisms are required to fight infection.
• Viruses enter the cytoplasm, hijack the host cells protein synthesis machinery and assemble new virus particles, which bud from the cell surface and infect new cells. Immune mechanisms which act in the extracellular space are ineffective once virus enters the cells.
• Intra-vesicular organisms (e.g. Mycobacteria) are taken up into cells but remain within vesicles, never entering the cytoplasm. Immune mechanisms that kill virus-infected cells are ineffective as the organisms are in a different cell compartment – therefore requiring an additional immune strategy.

Infecting organisms must first breach the body’s natural defences (skin, mucous membranes etc.). The pathogen then faces the two major types of immune response, the innate immune response, and the adaptive or specific immune response. When thinking about how these systems work it is helpful to consider (1) the recognition phase where the microorganism/ pathogen is recognised as foreign, and (2) the effector phase, which kills the organism.

The innate immune response is immediately available to fight pathogens without the requirement for prior exposure to the pathogen. This is the first line of defence against pathogens, recognising microbes by the presence of molecular patterns not present on mammalian cells. Innate immunity is moderately effective at controlling infection and does not improve with repeated exposure to a particular organism.

The adaptive immune response is refined and expanded after infection, taking several days to provide protection on first exposure to a particular pathogen. The cells and molecules produced are highly specific for the...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• List of Figures
• List of Tables
• List of Case Studies
• Acknowledgements
• Abbreviations
• Introduction
• Part 1 Basic Immunology
• Part 2 Clinical Immunology
• Part 3 Immunotechniques and Diagnostic Tests Used in Clinical Immunology
• Part 4 Treatment of Immunological Disorders
• Clinical Immunology – Future Prospects
• Glossary