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Autoimmunity

Topic updated on 05/20/17 2:15pm

Snapshot
  • A 46-year-old woman presents to her primary care physician with double vision and weakness. She reports her double vision occurs when watching television or reading a book, and her weakness is most severe at the end of the day. On physical exam, when asking the patient to look up for a few minutes, ptosis ensues. When applying a glove filled with ice on the ptosis, it improves. Laboratory testing is significant for autoantibodies directed against acetlycholine receptors. (Myasthenia gravis)
Introduction
  • Clinical definition
    • an adaptive immune response directed against self-antigens resulting in
      • autoimmune disease
  • Background
    • lymphocyte development in the central lymphoid organ is accompanied by
      • gene rearrangements that inevitably produce
        • lymphocytes that react to self-antigens
          • these lymphocytes are normally removed through a number of mechanisms (e.g., negative selection), and this is termed self-tolerance
            • autoimmunity results from an impairment in self-tolerance
  • Pathogenesis
    • an immune response is triggered by self-antigens (also called autoantigens)
      • which results in the production of
        • autoreactive effector cells and autoantibodies leading to
          • tissue damage and thus autoimmune disease
    • autoimmunity may be triggered by
      • failure of self-tolerance mechanisms and environmental causes (e.g., infection) in
        • genetically predisposed people
    • molecular mimicry
      • a phenomenon where antigens resemble molecules in the host
      • this results in the production of antigen-directed antibodies that
        • cross-react with the self-molecule
      • note that effector cells may be autoreactive as well if the processed pathogen peptide is similar to the host's peptides
      • one example is rheumatic fever, which results from
        • antibodies being directed against the M protein of S. pyogenes which
          • cross-react with self-molecules (e.g., in the heart valves)
Clinical Correlate
 
Select Autoimmune Diseases
Disease
Pathogenesis
Findings
Rheumatoid arthritis
  • Autoreactive T-cells act on antigens found in the synovium of the joint
  • Inflammatory arthritis
Graves' disease
  • Autoantibodies act on the thyroid stimulating hormone (TSH) receptor
  • Hyperthyroidism
Systemic lupus erythematosus
  • Autoantibodies and autoreactive T-cells act on
    • DNA
    • chromatin proteins
    • ribonucleoproteins
  • Vasculitis
  • Rash
  • Glomerulonephritis
Multiple sclerosis
  • Autoreactive T-cells act on
    • central nervous system antigens
  • Myelin sheath destruction and sclerotic plaque formation
Myasthenia gravis
  • Autoantibodies act on
    • acetylcholine receptors
    • muscle-specific tyrosine kinase
  • Fatigable muscles weakness
Type 1 diabetes mellitus
  • Autoreactive T-cells act on antigens found on
    • pancreatic islet cells
  • ↓ Insulin production
 


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