IMM2022 Lecture Notes - Lecture 1: Degranulation, Diabetes Mellitus Type 1, Interleukin 4
30 May 2018
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HYPERSENSITIVITES
Results in tissue damage or pathology that is associated with unwanted immune responses
and causes autoimmune diseases and allergy
Type I hypersensitivity
• Immediate hypersensitivity
• TH2, IgE, mast cells (derived mediators -> vasoactive amines;
loosens epithelial cells to allow fluid into tissues), eosinophils
(cytokine mediated inflammation)
• Allergic responses
Type II hypersensitivity
• Antibody mediated diseases
• Self-reactive antibodies
• IgM, IgG
• Antibodies -> destruction, activation or inhibition
• Complement and Fc receptor mediated recruitment and activation
of leukocytes, opsonisation and phagocytosis of cells
• Eg. Graves disease (excessive secretion of thyroid hormones)
Type III hypersensitivity
• Immune complex-mediated diseases
• Immune complexes of circulating antigens and IgM or IgG
antibodies deposited in vascular basement membrane
• Key characteristic: The presence of antibodies bound to antigen in
the circulation
• Complement and Fc receptor
• Occurs when antigen-antibody complexes that are not adequately
cleared by innate immune accumulates (excess antigens)
• Eg. SLE (autoantibodies generated to nuclear components combine
to form a complex)
Type IV hypersensitivity
• T cell-mediated diseases
• CD4 (cytokine mediated inflammation, can cause tissue injury) and
CD8 (T cell-mediated cytolysis, can cause cell death and tissue
injury)
• Macrophage activation and direct target cell lysis
• Tend to be localised to single area, localised inflammation,
stimulate T cells non-specifically.
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