Summary table of types of hypersensitivity reactions. 
Type 1
 - Mediators: lgE
 - Antigen Form: Soluble antigen
 - Mechanism of Action: Allergen-specific lgE causes mast-cell degranulation releasing histamine and other inflammatory mediators
 - Time Course: Immediate-phase: minutes, Late-phase: 8-12 hours
 - Examples: Anaphylaxis, Hay fever, Food allergies, Drug allergies, Eczema, Asthma
Type 2
 - Mediators: IgG/ IgM
 - Antigen Form: Cell-bound antigen
 - Mechanism of Action: IgG/lgM antibodies bind to cell antigens, leading to complement activation and destruction of the cell
 - Time Course: Hours to days
 - Examples: Acute transfusion reaction, Haemolytic disease of the newborn
Type 3
 - Mediators: Antigen-antibody complex
 - Antigen Form: Soluble antigen
 - Mechanism of Action: Antigen-antibody complexes are deposited in tissues where they activate complement chain causing local inflammation and recruitment of leucocytes
 - Time Course: Hours to days
 - Examples: Rheumatoid arthritis, Post-streptococcal glomerulonephritis, Systemic lupus erythematosus
Type 4
 - Mediators: T cells
 - Antigen Form: Soluble/cell bound antigen
 - Mechanism of Action: Antigen-presenting cells activate Th1/cytotoxic T cells. T-cells recruit macrophages and release inflammatory cytokines
 - Time Course: Days (delayed)
 - Examples: Contact dermatitis, Tuberculin test, Graft rejection

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