When a person is first exposed to a pathogen, the immune response may be insufficient to combat the disease. In the process, however, the lymphocytes that have specificity for that antigen are stimulated to divide many times and produce a clone.This is active immunity,and it can protect the person from getting the disease upon subsequent exposures.
It first became known in Western Europe in the mid-eighteenth century that the fatal effects of smallpox could be prevented by inducing mild cases of the disease. This was accomplished at that time by rubbing needles into the pustules of people who had mild forms of smallpox and injecting these needles into healthy people. Understandably, this method of immunization did not gain wide acceptance.
Acting on the observation that milkmaids who contracted cowpox—a disease similar to smallpox but less virulent (less pathogenic)—were immune to smallpox, an English physician named Edward Jenner inoculated a healthy boy with cowpox. When the boy recovered, Jenner inoculated him with what was considered a deadly amount of smallpox, to which the boy proved to be immune. (This was fortunate for both the boy— who was an orphan—and Jenner; Jenner's fame spread, and as the boy grew into manhood he proudly gave testimonials on Jen-ner's behalf.) This experiment, performed in 1796, began the first widespread immunization program.
A similar, but more sophisticated, demonstration of the effectiveness of immunizations was performed by Louis Pasteur almost a century later. Pasteur isolated the bacteria that cause anthrax and heated them until their virulence (ability to cause disease) was greatly reduced (or attenuated), although their antigenicity (the nature of their antigens) was not significantly changed (fig. 15.21). He then injected these attenuated bacteria into twenty-five cows, leaving twenty-five unimmunized. Several weeks later, before a gathering of scientists, he injected all fifty cows with the completely active anthrax bacteria. All twenty-five of the unimmunized cows died—all twenty-five of the immunized animals survived.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.