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35.4 Immune System Disorders
Lesson Objectives
Explain what happens when the immune system overreacts to harmless pathogens.
Describe how HIV is transmitted and how it affects the immune system.
Lesson Summary
When the Immune System “Misfires” Sometimes, the immune system
overreacts to otherwise harmless antigens. Three types of disorders are caused in this way.
The most common immune-system disorders are allergies, which occur when antigens
enter the body and bind to mast cells. The mast cells release histamines, which increase
the flow of blood and fluids to the area. This causes allergy symptoms.
Allergic reactions in the respiratory system can cause asthma, a dangerous chronic
disease in which the air passages narrow and breathing becomes difficult.
When the immune system makes a mistake and attacks the body’s own cells, an
autoimmune disease results. Autoimmune diseases include Type I diabetes, rheumatoid
arthritis, and lupus.
HIV and AIDS In the 1970s, clusters of cases of opportunistic diseases—diseases that
attack people with weakened immune systems—led to the discovery of a new disease called
acquired immunodeficiency syndrome (AIDS).
Research revealed that AIDS is an infectious disease caused by human immunodeficiency
virus (HIV). HIV attaches to receptors on helper T cells. Once inside the cells, HIV
copies itself and the new viruses infect more helper T cells.
HIV infection gradually leads to the death of more and more T cells. When a person’s T
cell count drops to about one-sixth the normal level, the person has AIDS.
HIV can only be transmitted through contact with infected blood, semen, vaginal
secretions, or breast milk.
When the Immune System “Misfires”
For Questions 1–5, complete each statement by writing the correct word or words.
1. An overreaction of the immune system to antigens of pollen and other harmless
substances is called a(n)
2. Sneezing, a runny nose, and watery eyes are symptoms of the
response in the
respiratory system.
3. Drugs called
counteract the effects of
produced by mast
4. A dangerous condition that affects the respiratory system and can be caused by allergies
is called
5. Examples of
triggers for allergic reactions include tobacco smoke,
pollution, molds, and pet dander.
6. What is an autoimmune disease?
7. Describe the advantage and disadvantage of treating an autoimmune illness such as lupus.
8. Complete the table about autoimmune diseases.
Autoimmune Diseases
Autoimmune Disease
Organ or Tissue That Is Attacked
Type I diabetes
Connective tissues around the joints
9. What does AIDS stand for?
10. What is the term that describes diseases that attack people with a weakened immune
11. List four body fluids that can transmit AIDS.
12. What behaviors prevent people from being infected with HIV?
13. Why is curing HIV infection so challenging? Explain your answer.
14. Complete the flowchart that summarizes the HIV infection process.
HIV attaches to host cell membranes with specific surface molecules.
Viral DNA enters nucleus, attaches to host DNA, and makes viral RNA.
New viruses bud off of host cell membrane and infect more cells.
Apply the Big idea
15. What is the key difference between an immunodeficiency disease and an autoimmune
disease? Provide an example of both types of disease in your response.