what are hypersensitivity or allergic reactions?
excessive or unusual immune reactions that cause tissue damage
what does sensitised mean?
the development of an immune response subsequent to exposure to an antigen
what is hypersensitivity?
when the immune system produces an excessive and damaging immune response to a harmless antigen
what three types of antigens does hypersensitivity usually occur to?
- harmless antigens from the environment (allergens)
- antigens from microbes
- antigens from own self (self-antigens)
what are the 4 types of hypersensitivity?
- allergic reaction
- cytotoxic hypersensitivity
- immune complex hypersensitivity
- cell-mediated/delayed hypersensitivity
explain type 1 hypersensitivity (allergic reaction)
- caused by production of IgE antibodies from B cells which bind to mast cells
- re-exposure to antigen causes it to attach to IgE sensitised mast cell = release of chemical mediators which = rapid inflammatory response
explain immune complex hypersensitivity?
- antigen + antibody = complex deposited into tissue, causing local inflammatory response
- soluble agents bind to antibodies, forming immune complex
- immune complexes lodges into blood vessels, joints + glomeruli, causing inflammatory process to start
explain cytotoxic hypersensitivity?
- antigen present on cell membrane, may be normal or foreign
- circulating IgG antibodies bind to antigens on patient’s cell surfaces
- these cells recognised by macrophages, then act as antigen-presenting cells, causing B cell response + antibody production against antigen
- cell then destroyed
explain cell-mediated/delayed hypersensitivity?
- delayed response by sensitised T cells to specific antigen = cytokine release + inflammatory response + destruction of antigen
- helper T cells recognise antigen on surface of APC
- CD4+ T cells secrete IL-2 + interferon = immune response
- activated T cytotoxic cells destroy target cells on contact
what is anaphylaxis?
a serious, life-threatening, systemic type 1 hypersensitivity reaction
explain the pathophysiology of anaphylaxis
- chemical mediators (histamines) released rapidly from mast cells within connective tissue, into general circulation
- general and/or systemic vasodilation occurs = sudden, severe onset of hypotension (low BP)
- in lungs, oedema of mucosa + bronchoconstriction = serious respiratory dysfunction
what is recommended treatment for anaphylaxis?
- noradrenaline (epinephrine) injection immediately
- antihistamine useful in early stages
briefly explain autoimmune disorders
these occur when excessive and inappropriate inflammatory reaction occurs against self-antigens
explain the mechanism of autoimmune disorders
- occur when individuals develop antibodies against own cells/cellular material
- self-tolerance to own antigens lost, thus immune system cannot discern self from non-self, auto-antibodies then trigger immune response, leading to inflammation + possible necrosis
what are immunomodulating agents?
agents that modify the body’s immune responsiveness
what are the two categories of immunomodulating agents?
- immunostimulants - increase immune responsiveness to fight cancer or infection
- immunosuppressants - suppress immune reactions associated with hypersensitivity reactions + autoimmune disease
true or false: immunosuppressant agents can be used to prevent rejection of transplanted tissues/organs, autoimmune diseases and hypersensitivity reactions?
true
what effect do corticosteroids have on the immune system?
- reduce size and contents of lymph nodes and spleen
- suppress T cell activity
- suppress macrophage activity
explain cyclosporin?
- cyclosporin belongs to group of immunosuppressants called calcineurin inhibitors
- it is actually an antibiotic but has immunpsuppressing actions
what is the mechanism of action of calcineurin inhibitors?
prevent proliferation of T cells after antigen presentation, done without affecting phagocytosis, sensitised T cell function or suppressing bone marrow cells
what are monoclonal antibodies?
those made by a single B cell clone, which makes each antibody identical and highly specific for one antigen
what does the suffix ‘_mab’ indicate?
that it is a monoclonal antibody
