Autoimmune Diseases and Mechanisms

Autoimmunity Overview

  • Definition: Autoimmunity is when the body's immune system fails to recognize its own cells and tissues, launching immune responses against them as if they were foreign invaders.

Mechanism of Autoimmunity

  • The condition involves the production of antibodies and T cell responses that target the body’s own tissues (autoantigens).
  • This leads to diseases or functional changes due to the immune system attacking normal components of the body.

Types of Autoimmune Diseases

  • Classification: Autoimmune diseases can be categorized into two classes:
    • Organ-Specific Diseases:
    • Immune response is directed against antigens in a single organ.
    • Examples:
      • Addison's Disease: Autoantibodies target the adrenal cortex.
      • Myasthenia Gravis: Immune response attacks neuromuscular junctions.
    • Systemic Diseases:
    • Immune response affects multiple organs.
    • Example:
      • Systemic Lupus Erythematosus: Characterized by inflammation affecting the skin, joints, kidneys, and other organs.

Causes of Autoimmune Diseases

  1. Antigen Sequestration:

    • Some body proteins remain hidden or isolated from immune detection. When they escape (due to trauma/infection), they can induce an immune response.
    • Example: Lens protein from the eye.

  2. Molecular Changes:

    • Tissues or cells undergo antigenic changes due to various influences, leading to new antigens that provoke immune responses.
    • Examples:
      • Immunoconglutinins (IKs): Autoantibodies against complement components (C2, C3, C4) that reflect the level of complement activation in serum.

  3. Molecular Mimicry (Cross-Reactivity):

    • Sharing of epitopes between infectious agents/parasites and body tissue antigens can lead to autoimmunity.
    • Example: Trypanosoma cruzi antigens that mimic mammalian neurons and heart muscle, causing nervous and heart disease.
    • Rheumatic Fever: An inflammatory autoimmune disease post-infection by group A Streptococcus, affecting the heart, joints, skin, and brain.

Common Autoimmune Diseases

  • Over 80 autoimmune diseases exist, characterized by long-term conditions with variable symptom severity.
  • Common Autoimmune Diseases:
    • Type 1 Diabetes Mellitus: Immune attack on insulin-producing pancreatic cells, requiring insulin injections by young adulthood.
    • Systemic Lupus Erythematosus (SLE): Development of autoantibodies affecting various tissues like joints, lungs, and kidneys.
    • Hashimoto's Disease: An autoimmune disorder leading to hypothyroidism, where the immune system damages the thyroid, reducing hormone production.