Lecture Notes: Autoimmunity and Organ Transplant Rejection

Autoimmunity

• Definition: Breakdown in distinguishing self from non-self.
• Self-tolerance:
  • B cells and T cells learn not to react with self-antigens.
  • T cells are deleted in the thymus if they react with self.
  • B cells undergo a similar process in the bone marrow.
• Loss of Self-Tolerance:
  • Leads to autoimmune disorders (Auto means self).
  • Can result in tissue damage.
• Triggers:
  • Infections can trigger autoimmune reactions, e.g., S. pyogens and M protein resemble heart proteins leading to rheumatic fever.
  • Mutations can alter self-epitopes, leading to immune activation against them.

Case Study: Systemic Lupus Erythematosus (SLE)

• Patient: Tamil, 26-year-old with joint pain and rash.
• Symptoms: Rash worsened by sun exposure, positive anti-nuclear antibody test.
• Diagnosis: High levels of self-antibodies indicated systemic lupus erythematosus.
• Mechanism: Antigen-antibody complexes form and trigger inflammation in tissues and organs.

Other Autoimmune Diseases

• Graves' Disease:
  • Autoantibodies bind to thyroid-stimulating hormone receptors causing hyperthyroidism (high metabolism).
• Hashimoto's Disease:
  • Autoantibodies damage the thyroid causing hypothyroidism (low metabolism).
• Myasthenia Gravis:
  • Autoantibodies block muscle receptors for acetylcholine causing muscle weakness.
• Type 1 Diabetes:
  • T cells attack pancreas cells leading to no insulin production (childhood onset, autoimmune).
• Rheumatoid Arthritis:
  • Antibodies and immune complexes cause inflammation in joint connective tissue leading to prolonged inflammation.

Organ Transplant Rejection

• Self vs. Non-Self Recognition:
  • Immune system recognizes MHC and identifies non-self MHC as foreign.
  • MHC compatibility crucial for organ transplants.
• Matching Donors:
  • Often seek close genetic matches to prevent rejection.
• Red Blood Cells:
  • Do not express MHC molecules, hence can be donated across individuals.
• Graft vs. Host Disease:
  • Donated organ might carry immune cells that attack the host.
• Immune Suppression:
  • Necessary to prevent the immune system from attacking transplanted organs.

Conclusion

• Next Topics:
  • How pathogens cause disease.
  • Detection of microbes and testing.
  • Epidemiology.

Key Takeaway

Understanding autoimmunity and organ transplant rejection is crucial in medical science, highlighting the importance of self-tolerance and compatibility in treatments.