Infection, Resistance, and Immunity, Second Edition

Julius Kreier

• Publisher: Routledge
• Year: 2022
• ISBN:
  9781351438612
• Edition: 1
• Topic: Medicine
• Subtopic: Medical Theory, Practice & Reference

Designed as an introductory textbook, Infection, Resistance and Immunity provides basic information on the workings of the immunological system and on infectious processes and their control. With sections on immunological disorders, immunization, immunodiagnosis, and epidemiology, it relates immunology to practical problems in medicine. The book includes a section on comparative immunology, introducing students to differences among immunological systems among common species of nonhuman animals. Written for the advanced undergraduate, the focus is on host-parasite interactions—distinguishing this text from other standard texts, which focus on the cellular mechanisms of the immune response.

CHAPTER 1

Introduction to Infection, Resistance, and Immunity

Samuel J. Black

INTRODUCTION

THE IMMUNE SYSTEM

Constitutive Immunity

Adaptive or inducible immunity

Vaccation

Passive immunity

HOST AND PATHOGEN INTERACTIONS

Immune Evasion Strategies of Pathogens

Host Selection by Disease

PUBLIC HEALTH MEASURES

Personal Health Measures

Impact of Public and Personal Health Measures on Pathogens

SUMMARY

SUGGESTIONS FOR FURTHER READING

QUESTIONS

ANSWERS

INTRODUCTION

This chapter is designed to provide an overview of the material that is covered in the rest of the text. We hope that it helps the student to grasp the field as a whole by tying together and integrating the material handled in the various chapters that follow. The student may find that rereading this chapter at various times as the course progresses will aid in obtaining a grasp of how the components of infection, resistance, and immunity work together to maintain our health.

THE IMMUNE SYSTEM

All life-forms on planet Earth are constructed from the same materials, and assembled in basically the same way. All compete for the same resources and each is rich in directly utilizable processed materials. Each life-form provides an opportunity for creative exploitation by others, Le., can enhance reproductive fitness of other life forms by being food or shelter, or by making iteasier to obtain food or shelter. In short, life-forms on this planet did not, and do not, get on by ignoring each other.

Although assembled from the same units, each speck of life flaunts its individuality through the array of molecules on its surface and announces its presence by a unique perfume of metabolites and other secretory products. From the very beginning, mutation and selection equipped life- forms with receptors to pick up cues from other life-forms, and with biochemical pathways that linked cue to response, be the response gene activation or movement to engulf and kill prey or release of secretions to capture scarce resources or to attract mates or to repel predators.

By the time metazoa arose through evolution, neighboring organisms were already equipped to perceive and prey on them, whilst the metazoa most likely had a variety of counterdefenses to frustrate this process. These primitive immune systems continued to develop during evolution under the selective pressure of pathogens. At present, numerous types of immune systems exist. They differ in fairly substantial ways between phyla and in more subtle ways between species (Table 1.1). The systems are least complex in invertebrates, which lack adaptive immune components, and most complex in mammals, which are the focus of this text. See chapter 13 (Comparative Immunology) for further discussion of this subject.

Table 1.1. The nature of lymphoid organs and of immune responses of vertebrates of various classes.

		Functional activity
Vertebrate Class	Lymphoid organs	Graft rejection	Antibody formation
Jawless fishes, e.g., hagfish	No thymus equivalent present	+/-	+
Cartilaginous fishes, e.g., sharks	Thymus equivalent present	+	+
Bony fishes	Spleen present Thymus equivalent present Spleen present Lymphoid cell aggregates present	+	+
Amphibians Newts/Salamanders	Thymus-like organ present Spleen present	+	+
Frogs/Toads	Thymus-like organ present Spleen present Lymph nodes present	+	+
Reptiles Alligators/Crocodiles	Spleen present Thymus not described Lymph nodes present	?	?
Lizards Aurtles/Snakes	Bursa-like organ present Thymus equivalent present	+	+
Birds	Bursa with a defined inner structure present Thymus and spleen present Lymph nodes present	+	+
Mammals	No bursa (bone marrow is the probable bursal equivalent) Thymus, spleen, lymph nodes, and lymphatic duct system all present	+	+

The immune system plays an essential role in ensuring our survival. We are exposed to viruses, bacteria, fungi, and parasites that can use our bodies both as niche and nutrient source. The level of exposure is regulated by public and personal health practices, but excellent public and personal health programs alone do not prevent disease. Even in our hygiene-conscious society, most individuals occasionally incubate infections. Individuals with defective immune systems, e.g., patients who have certain genetic defects, or are maintained on immunosuppressive therapy to prevent graft rejection, or who are infected with, for example, the immune system- destructive acquired immunodeficiency syndrome (AIDS) virus, can develop life- threatening disease often with organisms usually considered to be of little or no pathogenicity.

The immune system is our primary defense against disease. It is composed of interacting molecules, cells, and organs that can discriminate environmental agents (nonself) from one′s own tissues (self) and prevent or limit the extent to which the body is colonized by nonself. It is important to be aware that there are many components making up the immune system, each with its own set of functions. Some aspects and functions of the immune systems are outlined in Figure 1.1 and are listed below:

Constitutive Immunity: (1) Barrier Immunity—Prevents the initial invasion of the body by other organisms. (2) The Inflammatory Response—Rapidly responds to pathogens that bypass barrier immunity and creates conditions that limit their replication at the site of invasion.

Adaptive Immunity—Mounts, over a period of several days, immune responses that eliminate invading organisms and their products in a highly specific manner.

Passive Immunity—Protects the fetus and newborn from infection during the development of its immune system.

Figure 1.1. There are a variety of mechanisms by which organisms resist parasitization. The constitutive mechanisms (1) develop as the individual develops. The development is under endogenous control. The inducible mechanisms (2) develop only partially under endogenous stimuli and require contact with the parasite or its products for full development. The inducible mechanisms are commonly classified into active (2A) and passive (2B) forms depending on whether the individual develops its own immune mediators or receives those produced by another. Active and passive immunity may each be further divided into artificial (2A1 ; 2B1 ) and natural (2A2; 2B2) types. The artificial types are those that result from intervention by physicians or veterinarians.

Constitutive Immunity

Barrier Immunity

In this type of immunity, just as with martial arts, all parts of the body are used in defense and as weapons against the foe, here, disease-causing organisms. The surfaces that come into intimate contact with the environment both present a physical barrier to environmental pathogens and are endowed with antimicrobial activities. The skin of the frog and the silkworm contains short hydrophobic peptides, called cecropins, that lyse fragile protozoan parasites. Mammal skin is dotted with hair follicles and associated sebaceous glands that secrete antimicrobial lactic and fatty acids. Antimicrobial agents in sweat, tears, and saliva limit growth of microorganisms in these secretions. Pathogens that are inhaled are often trapped in mucin at mucosal surfaces, expelled back into the mouth, swallowed, and exposed to damaging treatment with acid, bile, and enzymes of the digestive tract. Sneezing, coughing, vomiting, diarrhea, and urination all play a role in removal of infectious agents from the body. Products of adaptive immune responses also participate in the maintenance of barrier immunity, e.g., pathogen-reactive antibodies of the IgA class, are secreted at mucosal surfaces and help to reduce infection by binding to structures on microbes that facili ta te invasion.

The Inflammatory Response

Mere physical and mechanical barriers are often an inadequate protection against disease and decay. We must beware the enemy that breaches them. Pathogens bypass barrier immunity when they enter the body through cuts, are transmitted directly into tissues by a biting insect, or invade cells lining the respiratory or alimentary passages after inhalation or consumption. Once in the body, pathogens encounter the constitutive defense processes that comprise the inflammatory response system. The infiamma tory mechanisms of defense are mediated by molecules and cells that activate when they contact damaged body tissues. The molecular basis of the response is similar whether tissue damage is wrought by heat, abrasion, Laceration, a biting insect, or a pathogen. The resulting reaction is called an inflammatory response.

The "weal and flare" that results from a minor skin scratch illustrates the speed, potency, and features of an infiammatory response. This reaction is characterized by redness, swelling, heat, and pain. Redness and heat are due to an increase in blood flow to the site of infiammation and result from local vasodila tion caused by chemical mediators produced in response to tissue damage. Swelling is due to leakage of blood fluids into the site of infiammation as a result of mediator- induced changes in the permeability of endothelial cells lining local blood vessels. Pain is due to tissue destruction exacerbated by proteolytic enzymes, lipolytic enzymes, and reactive oxygen intermediates released from cells (neutrophils, macrophages) that are recruited from the blood circulation into the inflammatory site. Prostaglandin E2 that is produced at the site of inflammation enhances sensitivity of local nerve cells also contributing to pain associated with inflammation. Pain itself is a defense mechanism. It calls attention to the damaged site and induces behavioral responses aimed at limiting damage and inducing avoidance of damaging behavior.

The scratch-induced "weal and flare" reaction is short-lived. That is not the case if the damaged tissues harbor pathogenic organisms, which typically have surface structures that interact with serum components to amplify production of the chemical mediators of inflammation.

Within an inflammatory site, invading organisms are exposed to damaging enzymes and oxygen radicals and can become coated with a series of serum enzymes (complement factors) that ultimately punch holes into their surfaces. The organisms can also be coated with fragments of complement such as C3b and iC3b, which cause them to be engulfed (phagocytosed) and destroyed by cells that are specialized for this activity, namely, neutrophils and macrophages. Once microbes are engulfed by phagocytic cells, they are exposed to a hostile environment comprising proteolytic enzymes, acid pH, reactive oxygen intermediates, nitric oxide, and antimicrobial peptides called defensins within the phagocytic cells. The majority of microbes cannot withstand these conditions. Antiviral agents (interferons) produced by cells participating in the inflammatory response help control viral infections in neighboring cells and enhance antibacterial activity of macrophages.

Adaptive or inducible immunity

Adaptive Immune Responses

Uncontrolled inflammatory responses can sometimes lead to debilitating tissue and organ damage, but the responses typically subside as organisms that provoke them are eliminated, and tissue damage is repaired. Elimination of invading pathogens usually requires the development of pathoge...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Contributors
• Chapter 1 - Introduction to Infection, Resistance, and Immunity
• Chapter 2 - Host-Parasite Relationships
• Chapter 3 - Constitutive Host Resistance
• Chapter 4 - The Inflammatory Response: A Bridge Between The Constitutive and Inducible Systems
• Chapter 5 - The Inducible System: History of Development of Immunology as a Component of Host-Parasite Interactions
• Chapter 6 - The Inducible System: Antigens
• Chapter 7 - The Inducible Defense System: Antibody Molecules and Antigen-Antibody Reactions
• Chapter 8 - The Inducible Defense System: The Induction and Development of the Inducible Defence
• Chapter 9 - Specific Host Restance: The Effector Mechanisms
• Chapter 10 - Immunologically Mediated Diseases and Allergic Reactions
• Chapter 11 - The Host Response to Grafts and Transplantation Immunology
• Chapter 12 - The Immunological System and Neoplasia
• Chapter 13 - Comparative Immunology
• Chapter 14 - Pathogenicity and Virulence
• Chapter 15 - Bacteria
• Chapter 16 - The Viruses
• Chapter 17 - The Parasitic Protozoa and Helminth Worms
• Chapter 18 - The Fungi
• Chapter 19 - Immunization
• Chapter 20 - Immunological Tests for Diagnosis of Disease and Identification of Molecules
• Chapter 21 - Epidemiology, Disease Transmission, Prevention, and Control
• Index