Immuno 3 Flashcards
(16 cards)
What is immunological tolerance?
Immunological tolerance is the non-reactivity of the immune system to specific antigens, due to a lack of lymphocyte response. It may result from deletion, anergy, immunological ignorance, or suppression.
Where does central tolerance occur and what does it involve?
Central tolerance occurs in the bone marrow (for B cells) and thymus (for T cells). It renders B and T cells non-responsive to self-antigens during development, involving deletion of autoreactive cells. Aire gene expression in thymic medullary epithelial cells is critical for T cell tolerance.
What is peripheral tolerance?
Peripheral tolerance occurs in peripheral tissues for both B and T cells. It includes deletion (apoptosis), anergy (non-responsiveness due to lack of co-stimulatory signals), and suppression (by regulatory T cells).
What is the mechanism of tolerance via deletion?
Deletion involves activation-induced death of T cells upon repeated antigen stimulation. Activated T cells express Fas and Fas Ligand, leading to apoptosis.
How does anergy contribute to immune tolerance?
Anergy occurs when antigen-presenting cells lack co-stimulatory signals, or when T cells express CTLA-4 instead of CD28. This results in T cell non-responsiveness, even with proper antigen presentation.
What is immune ignorance in the context of tolerance?
Immune ignorance is when self-antigens are located in immunologically privileged sites (e.g., eye lens, brain, heart). These antigens are not seen by the immune system, avoiding a response.
What is suppression in immune tolerance?
Suppression involves regulatory T cells (Tregs) that inhibit immune responses to maintain self-tolerance and prevent autoimmunity.
What causes autoimmunity?
Autoimmunity arises from a breakdown of immune tolerance, leading to adaptive immune responses against self-antigens. It includes systemic and organ-specific autoimmune diseases.
What is Graves’ disease?
Graves’ disease is an autoimmune condition where antibodies bind to thyroid-stimulating hormone (TSH) receptors, stimulating excess thyroid hormone production.
What is hypersensitivity and how is it classified?
Hypersensitivity is an exaggerated immune response that damages tissues. It includes four types: Type I (IgE/allergy), Type II (cytotoxic), Type III (immune complex), and Type IV (delayed-type/cell-mediated).
Describe Type I hypersensitivity.
Type I hypersensitivity is an immediate allergic reaction involving mast cells and IgE antibodies. It can be local or systemic (e.g., anaphylaxis). Symptoms appear within minutes upon re-exposure to the allergen.
What are the symptoms and risks of anaphylaxis?
Anaphylaxis involves rapid onset of symptoms like airway swelling and hypotension within 15–30 minutes. It can be fatal without epinephrine treatment.
How is allergy diagnosed?
Allergy is diagnosed via skin prick tests (wheal and flare in 15–30 mins) or ELISA blood tests measuring IgE levels.
Describe Type II hypersensitivity.
Type II involves IgG or IgM antibodies binding to cell surface antigens, leading to complement activation and cell lysis. Examples include hemolytic disease of the newborn and myasthenia gravis.
Describe Type III hypersensitivity.
Type III involves immune complexes (antibodies and soluble antigens) depositing in tissues, triggering complement and inflammation. Examples include rheumatoid arthritis and lupus.
Describe Type IV hypersensitivity.
Type IV is a delayed cell-mediated immune response (1–2 days) involving Th1 cells, cytotoxic T cells, and macrophages. It causes tissue damage. Examples include nickel allergy and the tuberculin skin test.
