Immune System II:
Immune System Diseases

Big Picture

Like any other system in the body, the immune system can have problems. Sometimes, the immune system can target the wrong types of cells, interpreting harmless substances as pathogens. Other times, damage can be done to the immune system itself, interfering with its ability to do its job. Such problems are called immune diseases. Some of these problems have cures and can be relieved. For others, investigation into effective cures is ongoing.

Key Terms

Allergy: Disease in which the immune system makes an inflammatory response to a harmless antigen.

Allergen: Any antigen that causes an allergy.

Autoimmune Disease: Type of disease, such as type 1 diabetes, in which the immune system attacks the body’s cells as though they were pathogens.

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

Human Immunodeficiency Virus (HIV): A virus transmitted through body fluids that infects and destroys helper T cells, eventually causing acquired immunodeficiency syndrome (AIDS).

Acquired Immunodeficiency Syndrome (AIDS): Disorder characterized by frequent opportunistic infections that eventually develops in people who are infected with human immunodeficiency virus (HIV).


An allergy is an inflammatory response to a harmless antigen (known as an allergen). Swallowing, inhaling, and/or touching an allergen can be enough to set off an allergic reaction. A mild allergic reaction can be treated with antihistamines, while a severe reaction requires emergency medical attention.
A few symptoms of an allergic reaction can be difficulty in breathing, skin irritation, and/or runny nose. In more severe cases, anaphylaxis, or shock, occurs. Shock occurs when the body is not getting enough blood because of low blood pressure.

Autoimmune Disease

Autoimmune diseases occur when the immune system recognizes harmless body cells as pathogens and attack them. When the immune system has been exposed to pathogens with antigens similar to those of the body cells, it mistakes the body cells’ antigens as those of the harmful microorganism. Some autoimmune diseases include type 1 diabetes, rheumatoid arthritis, multiple sclerosis, and systemic lupus erythematosus.


Immunodeficiency occurs when the immune system is unable to fight off pathogens that it should be able to. This may occur through a variety of reasons: a weakened immune system by old age, drug abuse, immune-suppressing medication, or an immune system-destroying pathogen (like HIV).
People are rarely predisposed to immunodeficiency. Most of the time, victims acquire it over a lifetime.


HIV (human immunodeficiency virus) is a disease that attacks the immune system, or more specifically, the T cells of the immune system. HIV can be transmitted by bodily fluids such as breast milk, semen, and blood. When the virus enters the body, it targets T cell and infects the T cell with its DNA (as any virus does). By doing so, the T cell is destroyed and creates new several new HIV viruses, which then go on to infect the rest of the body’s T cells. As a result, the immune system is compromised (as T cells are very important agents of the immune system).
Perhaps the most frightening thing about HIV is its ability to evade the immune system’s defense mechanisms. Antigens on regular pathogens mark them for destruction. However, HIV is constantly mutating, so its antigens are constantly changing and makes targeting the virus difficulty. The virus can also hide its antigens using the plasma membrane of its host cell.

  • Often people believe that HIV can be contracted by exposure to an HIV positive person’s sweat, air, or saliva. However, HIV can only be spread through bodily fluids such as semen, vaginal fluids, blood, and breast milk.
  • While treatment to relieve symptoms and extend the life of an HIV patient is available, these treatments are expensive and often present serious side effects. A true HIV cure is still under investigation.
  • The symptoms of HIV can take years to appear.

AIDS (acquired immune deficiency syndrome) is the result from years of damage to the immune system by HIV. The weakened immune systems cannot fight back from opportunistic diseases (diseases that are rare except in people with immunodeficiency), and opportunistic diseases are often the direct cause of death for people with AIDS.