Immunology is the study of the body’s defense against infection. We are continually exposed to microorganisms, many of which cause disease, and yet become ill only rarely. How does the body defend itself? When infection does occur, how does the body eliminate the invader and cure itself? And why do we develop long-lasting immunity to many infectious diseases encountered once and overcome? These are the questions addressed by immunology, which we study to understand our body’s defenses against infection at the cellular and molecular levels.
The beginning of immunology as a science is usually attributed to Edward Jenner for his work in the late 18th century (Fig. 1.1). The notion of immunity— that surviving a disease confers greater protection against it later—was known since ancient Greece. Variolation—the inhalation or transfer into superficial skin wounds of material from smallpox pustules—had been practiced since at least the 1400s in the Middle East and China as a form of protection against that disease and was known to Jenner. Jenner had observed that the relatively mild disease of cowpox, or vaccinia, seemed to confer protection against the often fatal disease of smallpox, and in 1796, he demonstrated that inoculation with cowpox protected the recipient against smallpox. His scientific proof relied on the deliberate exposure of the inoculated individual to infectious smallpox material two months after inoculation. This scientific test was his original contribution.
Jenner called the procedure vaccination. This term is still used to describe the inoculation of healthy individuals with weakened or attenuated strains of disease-causing agents in order to provide protection from disease. Although Jenner’s bold experiment was successful, it took almost two centuries for smallpox vaccination to become universal. This advance enabled the World Health Organization to announce in 1979 that smallpox had been eradicated (Fig. 1.2), arguably the greatest triumph of modern medicine.
Jenner’s strategy of vaccination was extended in the late 19th century by the discoveries of many great microbiologists. Robert Koch proved that infectious diseases are caused by specific microorganisms. In the 1880s, Louis Pasteur the origins of vertebrate immune cells. Principles of innate immunity.
Principles of adaptive immunity. the effector mechanisms of immunity.
Fig. 1.1 Edward Jenner. Portrait by John raphael Smith. reproduced courtesy of yale university, Harvey Cushing/John Hay Whitney medical library.
Number of countries with one or more cases
Fig. 1.2 The eradication of smallpox by vaccination. After a period of 3 years in which no cases of smallpox were recorded, the World Health organization was able to announce in 1979 that smallpox had been eradicated, and vaccination stopped (upper panel). A few laboratory stocks have been retained, however, and some fear that these are a source from which the virus might reemerge. Ali maow maalin (lower panel) contracted and survived the last case of smallpox in Somalia in 1977. Photograph courtesy of dr. Jason Weisfeld.
devised a vaccine against cholera in chickens, and developed a rabies vaccine that proved to be a spectacular success upon its first trial in a boy bitten by a rabid dog.
These practical triumphs led to a search for vaccination’s mechanism of protection and to the development of the science of immunology. In the early 1890s, Emil von Behring and Shibasaburo Kitasato discovered that the serum of animals immune to diphtheria or tetanus contained a specific ‘antitoxic activity’ that could confer short-lived protection against the effects of diphtheria or tetanus toxins in people. This activity was later determined to be due to the proteins we now call antibodies, which bind specifically to the toxins and neutralize their activity. That these antibodies might have a crucial role in immunity was reinforced by Jules Bordet’s discovery in 1899 of complement, a component of serum that acts in conjunction with antibodies to destroy pathogenic bacteria.