IMMUNOLOGY - Roitt I. - Mir 2000

Chapter 1. Introduction to the Immune System

VACCINATION

The fastest and most successful application of immunological research has been in the field of vaccine prophylaxis against infections. THE PRINCIPLE OF vaccination relies on two key characteristics of acquired Immunity: immunological Specificity and memory. Thanks to memory Cells, The Immune System is capable of mounting a much stronger response upon re-exposure to a given antigen. This secondary response develops more rapidly and is more effective than the primary one.

When developing a vaccine, it is necessary to modify the microbe or its toxin so that they become harmless while retaining their antigenicity. This is possible because Antibodies and T cells recognize distinct parts of Antigens, known as epitopes, rather than the entire microorganism or toxin. Consider, for example, vaccination against diphtheria. The bacterium that causes diphtheria produces a toxin that destroys many types of cells, including Muscle cells. This toxin can be modified by formaldehyde Treatment so that it loses its toxicity while preserving its epitopes; the resulting toxoid is used as the diphtheria vaccine (Fig. 1.19). Another approach is to attenuate (weaken) an infectious agent, such as the poliovirus, to the point where it loses its pathogenicity while retaining its antigenicity. The challenges of vaccination are discussed in more detail in Chapter 19.

Class="center">

Fig. 1.19. The principle of vaccination, illustrated using diphtheria toxoid immunization as an example. Through chemical modification, diphtheria toxin is converted into a toxoid that retains the toxin's epitopes but loses its toxicity. Vaccination with such a toxoid induces the primary production of antibodies against the toxin's epitopes. In the event of subsequent natural infection with diphtheria, the toxin restimulates memory B cells, eliciting a secondary, faster, and enhanced production of antibodies that neutralize the toxin.