Active Immunization Vs. Passive Immunization

Difference Between Active Immunization And Passive Immunization
The human body is quick to recognize foreign organisms that enter it. “Foes” must be attacked or otherwise got rid of. The most common of these foes are viruses, bacteria, and other microscopic organisms. The body recognizes these foes by the chemicals within them called antigens. To counteract these foreign invaders, the body produces its own chemicals, protein molecules called antibodies. Each kind of antigen causes the production of a specific kind of antibody. Antibodies appear in the body fluids such as blood and lymph and in the body’s cells.
Doctors learned to make use of the antibody system for defense against invaders long before they had any idea that antibodies existed. As early as 1796, Edward Jenner, an English country doctor, discovered that if he gave people a case of the mild disease cowpox, he prevented them from getting the serious disease smallpox. What Jenner did not know is that the diseases are caused by closely related viruses. They are so closely related that the cowpox antibody will counteract the smallpox antigen.
Injecting an antigen to start the production of antibodies is now called vaccination. (It is one kind of immunization—making a person immune.) The antigen injected is a vaccine. These terms are based on vacca, the Latin word for “cow,” because Jenner’s vaccine was made from the cowpox virus.
Today doctors know of several ways that people become immune to diseases. Some people inherit a natural resistance to certain diseases. Over the years they build up an immunity that keeps them from ever getting certain diseases. But most antibodies are acquired only after the body has been exposed to a known antigen. The antigen may be carried by some organism that enters the body on its own, or the antigen may be artificially injected with a needle.
When a specially prepared antigen is injected into a person, it is called active immunization. The person actively produces the antibodies that fight off the foreign matter. The antibody defense system then remains on the alert, ready to deal with any later invasion. This procedure can be used to protect people against a number of diseases, including measles, mumps, tetanus, poliomyelitis, diphtheria, chicken pox, whooping cough, hepatitis A, and hepatitis B.
Antibodies may also be produced in animals by injecting them with antigens. The antibodies are then transferred directly to a person. These antibodies are immediately ready for action. This is called passive immunization because the person plays no part in the production of antibodies. Passive immunization disappears within a few weeks. Active immunization gives much more lasting protection.
The substance taken from the immunized animal or person for passive immunization is called antiserum. If used early enough, it can prevent such diseases as measles and tetanus. Sometimes an antiserum can be used after the antigen has entered a person’s body, as in measles, tetanus, and diphtheria. Antiserums against bee and snake venom have also been developed.
Both antigens and antibodies are large molecules. Scientists believe that the antibody molecule combines with a particular antigen molecule, the two fitting like a key and a lock. In the chemical reaction that takes place, the antigen loses its power to cause the disease.

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