Developing Active Immunity to Infectious Disease 1955

Infections are the most common cause of human disease. They range from the common cold and influenza to debilitating conditions like chronic hepatitis and Lymes disease to life-threatening diseases such as AIDS. Immunity to a disease is achieved through the presence of antibodies to that disease in a persons system. Antibodies are proteins produced by the body to neutralize or destroy toxins or disease-carrying organisms. Antibodies are disease-specific. Long ago, physicians realized that people who had recovered from the plague would never get it again—they had acquired immunity. This is because some of the activated T and B cells had become memory cells. Memory cells ensure that the next time a person meets up with the same antigen, the immune system is already set to demolish it. Immunity can be strong or weak, short-lived or long-lasting, depending on the type of antigen it encounters, the amount of antigen, and the route by which the antigen enters the body. Immunity can also be influenced by inherited genes. When faced with the same antigen, some individuals will respond forcefully, others feebly, and some not at all. An immune response can be sparked not only by infection but also by immunization with vaccines. Some vaccines contain microorganisms—or parts of microorganisms— that have been treated so they can provoke an immune response but not full-blown disease. Immunity can also be transferred from one individual to another by injections of serum rich in antibodies against a particular microbe (antiserum). For example, antiserum is sometimes given to protect travelers to countries where hepatitis A is widespread. The antiserum induces passive immunity against the hepatitis A virus. Passive immunity typically lasts only a few weeks or months. For more information on the human immune system and vaccines, go to the website of the US National Institute of Allergy and Infectious Diseases (NIAID) at http://www3.niaid.nih.gov/topics/immuneSystem/ . This is clipped from the 1955 film Immunization (2nd Ed) produced by Encyclopedia Britannica Film and available at the Internet Archive.

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