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13.56: Immunodeficiency

Difficulty Level: At Grade Created by: CK-12
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Which is stronger?

You or little tiny pathogens? Usually you are. Normally your body can put up a strong defense against enemy pathogens. But what if it can't? What happens if your immune system is "sick"?


Immunodeficiency occurs when the immune system is not working properly. As a result, it cannot fight off pathogens that a normal immune system would be able to resist. Rarely, the problem is caused by a defective gene. More often, it is acquired during a person’s lifetime. Immunodeficiency may occur for a variety of reasons:

  • The immune system naturally becomes less effective as people get older. This is why older people are generally more susceptible to disease.
  • The immune system may be damaged by other disorders, such as obesity or drug abuse.
  • Certain medications can suppress the immune system. This is an intended effect of drugs given to people with transplanted organs. In many cases, however, it is an unwanted side effect of drugs used to treat other diseases.
  • Some pathogens attack and destroy cells of the immune system. An example is the virus known as HIV. It is the most common cause of immunodeficiency in the world today.

Compromised immune systems are discussed at http://www.youtube.com/watch?v=usRofaZEteY (2:36).


  • In an immunodeficiency disease, the immune system does not work normally. As a consequence, it cannot defend the body.


Use this resource to answer the questions that follow.

  • http://www.hippocampus.org/Biology Biology for AP* Search: Disorders of the Immune System
  1. What are immunodeficiency diseases?
  2. Describe SCID.
  3. What is leukemia? Why are individuals with leukemia immunodeficient?
  4. How does HIV affect the immune system?


1. List three possible reasons for acquired immunodeficiency.

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HIV (human immunodeficiency virus)

Virus transmitted through body fluids that infects and destroys helper T cells and eventually causes acquired immunodeficiency syndrome (AIDS).


Inability of the immune system to fight off pathogens that a normal immune system would be able to resist.

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Difficulty Level:
At Grade
Date Created:
Feb 24, 2012
Last Modified:
Aug 28, 2016
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