Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 43.4 Disruptions in Immune System Function Can Elicit or Exacerbate Disease
While the immune system usually protects the body, disruptions such as allergies, autoimmune diseases, and immunodeficiencies can lead to harmful effects. Additionally, some pathogens evolve to evade immune detection, and certain cancers are linked to immune suppression.
1. Allergies
- Allergies are hypersensitive immune responses to allergens
- IgE antibodies bind to mast cells, which release histamine when allergens cross-link the IgE
- Symptoms: sneezing, runny nose, inflammation, muscle contraction
- Anaphylactic shock is a severe allergic reaction, treatable with epinephrine
- Antihistamines block histamine receptors to reduce symptoms
2. Autoimmune Diseases
- Immune system attacks self-molecules
- Lupus: antibodies against DNA/histones
- Type 1 diabetes: attack on pancreatic beta cells
- Multiple sclerosis: attack on myelin sheaths
- Rheumatoid arthritis: joint inflammation
- More common in women; influenced by genetics and environment
- Regulatory T cells (Tregs) help suppress self-reactive responses
3. Immunodeficiency Diseases
- Inborn: genetic defects (e.g., SCID) → lacking functional lymphocytes
- Acquired: caused by infections (e.g., HIV), cancers (e.g., Hodgkin’s), or immunosuppressive drugs
- AIDS (acquired immunodeficiency syndrome) results from HIV, which infects and kills helper T cells
- HIV evades immunity via high mutation rate and latency
- Loss of helper T cells impairs both humoral and cell-mediated immunity
4. Pathogen Evasion Strategies
- Antigenic variation: pathogens (e.g. Trypanosoma, influenza virus) change surface proteins to avoid detection
- Latency: viruses (e.g. herpes simplex) remain dormant in host cells, reactivating under stress
- Direct attack: HIV infects immune cells using CD4, integrates into genome, and eventually disables immune responses
5. Cancer and the Immune System
- Immune suppression increases risk of virus-associated cancers (e.g., Kaposi’s sarcoma in AIDS patients)
- Immune system detects virus-derived antigens in some cancers
- Vaccines like those for HPV and hepatitis B reduce cancer risk
6. ABO Blood Groups and Transfusions
- Mismatched transfusions cause immune reactions due to recognition of foreign carbohydrates on red blood cells
- Type A has anti-B antibodies; Type O has both anti-A and anti-B
- Enzymes that remove A/B sugars may allow universal transfusion in the future
7. Monoclonal Antibodies and Immune Tools
- Monoclonal antibodies are lab-made, identical antibodies used in diagnostics and treatments
- Used in pregnancy tests, cancer therapies, and virus history screening from a single blood drop
In a Nutshell
Immune system disorders arise from imbalances in regulation—overreaction (allergies), misrecognition (autoimmunity), or underperformance (immunodeficiency). Pathogens evolve to escape detection, while viruses can even trigger cancers. Understanding and manipulating immune responses has led to advances like vaccines, antibody therapies, and better transplant management.