Introductory Immunology

Basic Concepts for Interdisciplinary Applications

Jeffrey K. Actor

• Publisher: Academic Press
• Year: 2019
• ISBN:
  9780128172810
• Edition: 2
• Topic: Medicine
• Subtopic: Immunology

Introductory Immunology: Basic Concepts for Interdisciplinary Applications, Second Edition is a completely updated, revised and expanded resource on the immune system as a primary defense for the maintenance of health and homeostasis. The book highlights the components of the human immune system and how they work together to confer protection against pathogenic invaders. It also creates an understanding of the basis for clinical tests and immune therapeutics and their importance in identifying and treating disease states. This updated edition will strengthen the foundation required to understand the placement of immune function within clinical practice, thus allowing a basic platform to define therapeutic treatments.

• Creates appreciation for the components of the human immune system that work together to confer lifelong protection
• Provides core knowledge in immunology to build a foundation to explore mechanisms involved in clinical disease
• Breaks down all immunology concepts into manageable, logically digestible building blocks
• Geared toward readers without medical, biochemical or cellular expertise
• Includes a glossary that provides functional definitions of complex terms

Chapter 1

A Functional Overview of the Immune System and Immune Components

Abstract

This chapter establishes a foundation to appreciate how components of the immune system work together to protect against the development of clinical disease. The basic systems and cells involved in immune responses are presented as a general overview of functional immunity. Components and systems presented include concepts of innate (always present) and adaptive (inducible and specific) responses, myeloid and lymphoid cells, and an introduction to immune anatomy.

Keywords

Innate immunity; Adaptive immunity; Myeloid; Lymphoid; Lymphocyte; Lymphoid organs; Cluster of differentiation (CD)

Chapter Focus

To establish a foundation to appreciate how components of the immune system work together to protect against the development of clinical disease. The basic systems and cells involved in immune responses will be presented in this chapter to give a general overview of functional immunity. Components and systems will be defined to allow an understanding of concepts of innate (always present) and adaptive (inducible and specific) responses, and how these responses interact with one another to form the basis for protection against disease.

Immune Homeostasis

A functional immune system offers constant surveillance of human beings in relationship to the world. It confers a balanced state of health through effective elimination of infectious agents (bacteria, viruses, fungi, and parasites) and through control of malignancies. Indeed, the immune system has evolved to allow cells and organs to interact with the environment to protect against harmful invaders. At the same time, mechanisms are in place to instill tolerance toward the naturally occurring microbiome (i.e., microbial and viral agents) that reside within us in symbiotic ways. Taken together, these responses represent a balance of components that ward off the development of clinical disease.

Self versus Nonself

Discrimination between the self and the nonself is considered the chief function of the immune system. We are under constant assault by invaders. Our bodies represent prime substrates for organisms to grow and reside, with an abundance of nutrients, warmth, and protection from the outside elements. The immune system is basically a series of obstacles to limit and inhibit pathogen entry and then to attack and destroy those organisms once they enter the body. The immune response is exquisitely designed to recognize these invaders as “foreign.” In fact, the major feature that renders our immune system so effective is its ability to distinguish our body's own cells (the self) from that which it considers foreign (termed the nonself). Each of our cells carries specific tags, or molecular markers, that label it as “self.” These markers are important, as they not only determine what is unique about us, but they also distinguish one person from another.

Almost anything and everything that registers as “nonself” will trigger an immune response. An intricate system of molecular communication and cellular interactions allows immune components to function in concert to combat disease-causing organisms. The foreign agent (microbe, virus, parasite, etc.), or any part of it that can be specifically recognized, is called an antigen. Simply put, an antigen is defined as any substance or physical structure that can be recognized by the immune system. Major classes of antigens include proteins, carbohydrates, lipids, and nucleic acids. If an antigen is of high complexity and weight, it can trigger full immune activity and become immunogenic.

The ability to distinguish our own cells from the outside world is critical to maintaining functional protection. If this ability is lost (e.g., when “self” tissue is seen as foreign), then our immune system launches an aggressive response against our own tissues. This is what happens during autoimmunity, where destruction of the self leads to clinical disease.

The immune system maintains a balance of responsiveness. Too little a response is ineffective, while too aggressive a response can lead to targeted destruction of bystander tissues. Both scenarios are equally as devastating and may result in clinical disease. The regulation of immune function and overall immuno-homeostasis is under the control of multiple factors, including genetic components and environmental cues. The intensity and duration of the responses must be sufficient to protect against invading pathogens, with prompt and specific downregulation when the foreign material (the antigen or the pathogen) is no longer present. The clinical state that arises when immune responses are not properly regulated is termed hypersensitivity, a state of excessive or inappropriate responses leading to disease. As one might imagine, hypersensitivity can occur in many different forms, depending upon which arm of the immune system is dysregulated.

Innate and Adaptive Immunity

The immune system is loosely divided into two major functional categories termed innate and adaptive immunity. Innate immune mechanisms provide the first line of defense from infectious diseases (Table 1.1). The innate immune components exist from birth and consist of components available prior to the onset of infection. These defensive components include both physical barriers and biochemical factors. Defensive innate mechanisms may be anatomic (skin, mucous membranes), physiologic (temperature, low pH, chemical mediators), phagocytic (digestion of micro...