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Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001.

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Immunobiology: The Immune System in Health and Disease. 5th edition.

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Chapter 10Adaptive Immunity to Infection

Throughout this book we have examined the individual mechanisms by which both the innate and the adaptive immune responses function to protect the individual from invading microorganisms. In this chapter, we consider how the cells and molecules of the immune system work as an integrated defense system to eliminate or control the infectious agent and how the adaptive immune system provides long-lasting protective immunity. This is the first of several chapters that consider how the immune system functions as a whole in health and disease. Subsequent chapters will examine how failures of immune defense and unwanted immune responses occur, and how the immune response can be manipulated to benefit the individual.

In the first part of this chapter, we briefly consider the diversity of pathogens the immune system can encounter and outline the general course of an infection. The mechanisms of innate immunity, which we discussed in detail in Chapter 2, are brought into play in the earliest phases of the infection and may succeed in repelling it. Pathogens, however, have developed strategies that allow them, at least on occasion, to elude or overcome the mechanisms of innate immune defense and establish a focus of infection from which they can spread. In these circumstances, the innate immune response sets the scene for the induction of an adaptive immune response, the focus of the second part of the chapter. Several days are required for the clonal expansion and differentiation of naive lymphocytes into effector T cells and antibody-secreting B cells that, in most cases, effectively target the pathogen for elimination (Fig. 10.1). During this period, specific immunological memory is also established. This ensures a rapid reinduction of antigen-specific antibody and armed effector T cells on subsequent encounters with the same pathogen, thus providing long-lasting protection against reinfection.

Figure 10.1. The course of a typical acute infection.

Figure 10.1

The course of a typical acute infection. 1. The level of infectious agent increases as the pathogen replicates. 2. When numbers of the pathogen exceed the threshold dose of antigen required for an adaptive response, the response is initiated; the pathogen (more...)

Innate immunity is an essential prerequisite for the adaptive immune response, as the antigen-specific lymphocytes of the adaptive immune response are activated by co-stimulatory molecules that are induced on cells of the innate immune system during their interaction with micoorganisms. The cytokines produced during these early phases also play an important part in stimulating the subsequent adaptive immune response and shaping its development; determining, for example, whether the response is predominantly T cell-mediated or predominantly humoral. We have already described the generation and function of effector T cells and antibodies in Chapters 8 and 9. In this chapter, we will discuss how the different phases of host defense are orchestrated in space and time, and how changes in specialized cell-surface molecules and chemokines guide lymphocytes to the appropriate site of action at different stages of the adaptive immune response.

The most frequent site of encounter between the body and microorganisms and other antigens is the mucosal immune system. This lines the airways, gastrointestinal tract, and urogenital system and is the most extensive compartment of the immune system. The third part of the chapter describes the functions and properties of the adaptive immune responses mounted by the mucosal immune system. These not only protect the body from infection, but are also designed to stop the immune system from responding inappropriately to the many environmental antigens and potential allergens with which the mucosal lymphoid tissues come into contact, most particularly the foods we eat every day.

We return to immunological memory that provides long-lasting and sometimes life-long protection against reinfection by many pathogens in the last part of the chapter. Memory responses differ in several ways from primary responses and we will discuss the reasons for this, and what is known of how immunological memory is maintained.

Contents

  • Infectious agents and how they cause disease
  • The course of the adaptive response to infection
  • The mucosal immune system
  • Immunological memory
  • Summary to Chapter 10
  • General references
  • Section references

By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.

Copyright © 2001, Garland Science.
Bookshelf ID: NBK10758

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