Autoimmunity in Haematology

Autoimmunity

• Autoimmunity is a misdirected immune response that occurs when the immune system attacks the body itself.
• It is a hypersensitivity reaction triggered by self-antigens.
• Molecular mimicry is a mechanism that can lead to autoimmunity, where a foreign antigen initiates an immune response, and a T- or B-cell component cross-recognizes self-antigens, leading to an autoimmune disease.

Tolerance

• The body has mechanisms to remove self-reactive T- and B-cells to prevent autoimmunity.
• Central tolerance is the mechanism that deletes self-reacting lymphocytes in the early stages of lymphocyte development (in thymus or bone marrow).
• Peripheral tolerance is a "safety net" that removes self-reactive lymphocytes that have escaped central tolerance, induced in mature lymphocytes, and involves T-regulatory cells (Tregs) that suppress autoreactions.

Classification of Autoimmune Conditions

• Autoimmune conditions are classified similarly to hypersensitivity reactions, with the exception of type I hypersensitivity.
• There are three types of autoimmune conditions:
  • Antibody-mediated (Type II) hypersensitivity reactions
  • Immune-complex mediated (Type III) hypersensitivity reactions
  • Cell-mediated (Type IV) hypersensitivity reactions

Antibody-Mediated (Type II) Hypersensitivity Reactions

• Antibody-mediated reactions occur when an antibody reacts to self-antigens, binds to tissue/cells, and results in opsonisation and complement activation.
• Example: autoimmune haemolytic anaemia.

Immune-Complex Mediated (Type III) Hypersensitivity Reactions

• Immune-complex mediated reactions occur when immune complexes are not cleared rapidly, leading to inflammation and tissue damage.
• Example: systemic lupus erythematosus (SLE).

Cell-Mediated (Type IV) Hypersensitivity Reactions

• Cell-mediated reactions occur when autoimmune T-cell responses lead to inflammation and tissue damage.
• Examples: rheumatoid arthritis, type I diabetes mellitus.

Ocular Autoimmune Diseases

• Mooren's ulcer: a rare disorder characterized by a painful, relentless, chronic ulcerative keratitis.
• Sympathetic ophthalmia: a bilateral granulomatous uveitis that occurs after a penetrating injury to one eye, potentially blinding.

Systemic Autoimmune Diseases

• Keratoconjunctivitis sicca: a dry eye syndrome characterized by dryness, corneal examination may reveal punctate erosive keratopathy or filaments.
• Scleritis: inflammation of the sclera, characterized by pain, tenderness, and decreased vision.
• Rheumatoid arthritis: a chronic inflammatory disorder that affects the joints, skin, eyes, lungs, heart, and blood vessels.
• Sjögren's syndrome: an autoimmune condition characterized by dry eyes and a dry mouth, affecting the mucous membranes and moisture-secreting glands of eyes and mouth.
• Graves' disease: an autoimmune condition resulting in hyperthyroidism, characterized by inflammation and congestion of periocular and orbital soft tissue.
• Systemic lupus erythematosus (SLE): a chronic inflammatory disease that can affect multiple organ systems, including the eyes.

This quiz covers the concepts of autoimmunity, including definitions, pathogenesis, classification, and ocular and systemic autoimmune conditions. It is a useful resource for students of haematology and cell biology.