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Immune Disorders: Immunodeficiencies, Autoimmunity, and Hypersensitivities

← Builds on Adaptive Immunity: B and T Cells, Antibodies, and Immune Memory

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  1. 1Start here
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The immune system is essential for defending the body against infections and diseases. However, when it malfunctions, it can lead to immune disorders such as immunodeficiencies, autoimmunity, and hypersensitivities. Immunodeficiencies occur when the immune system is weakened or absent, making individuals more susceptible to infections and certain cancers. Autoimmune diseases arise when the immune system mistakenly attacks the body's own tissues, causing inflammation and damage. Hypersensitivities are overreactions of the immune system to harmless substances, leading to conditions like allergies and asthma. Understanding these disorders is crucial because they affect millions of people worldwide and can significantly impact quality of life. By studying these immune-related conditions, we can better diagnose, treat, and manage them to improve health outcomes.

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Rheumatoid arthritis
Figure 21.1 The Worldwide AIDS Epidemic (a) As of 2008, more than 15 percent of adults were infected with HIV in certain African countries. This grim picture had changed little by 2012. (b) In this scanning electron micrograph, HIV virions (green particles) are budding off the surface of a macrophage (pink structure). (credit b: C. Goldsmith)

The immune system can go wrong in three main ways: immunodeficiencies, autoimmunity, and hypersensitivities. Immunodeficiencies happen when the immune system is too weak or missing, making it hard to fight infections or cancer. Hypersensitivities are overreactions to harmless things like pollen or food, leading to allergies or asthma.

Immunodeficiencies can be born with or caused by diseases like HIV. Autoimmune diseases include conditions like lupus or type 1 diabetes, where the immune system targets specific organs or cells. Hypersensitivities are divided into four types based on how the immune system reacts.

Type I, like allergies, happens quickly and involves IgE antibodies. Other types involve different immune cells and take longer to show symptoms. Understanding these disorders helps explain why some people get sick more often, why others have chronic inflammation, or why some reactions are severe.

It also shows how treatments like immunoglobulin infusions, allergy shots, or immune-suppressing drugs can help.

Key Points

  • HIV/AIDS is a secondary immunodeficiency caused by the human immunodeficiency virus, which compromises the immune system and leads to an increased susceptibility to opportunistic infections and certain cancers.
  • Common variable immunodeficiency is a primary immunodeficiency characterized by impaired antibody production, leading to recurrent infections and an increased risk of autoimmune disorders.
  • Severe combined immunodeficiency is a primary immunodeficiency where both T and B cell functions are severely impaired, resulting in a high risk of life-threatening infections.
  • Multiple sclerosis is an autoimmune disease in which the immune system attacks the myelin sheath of nerve fibers in the central nervous system, leading to communication problems between the brain and the rest of the body.
  • Rheumatoid arthritis is an autoimmune disease that primarily targets the joints, causing persistent inflammation that results in joint damage and pain, and can also affect the heart, lungs, and eyes.
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