Type I hypersensitivity
Classification and external resources
SEM of miscellaneous plant pollens. Pollens are very common allergens.
MeSH	D006969

Hypersensitivity types
Type I - Allergy (immediate)
Type II - Cytotoxic, antibody-dependent
Type III - Immune complex disease
Type IV - Delayed-type hypersensitivity (Antibody Independant)
Type V - Autoimmune disease

Type I hypersensitivity (or immediate hypersensitivity) is an allergic reaction provoked by reexposure to a specific type of antigen referred to as an allergen.^[1]

Exposure may be by ingestion, inhalation, injection, or direct contact.

Contents 1 Pathophysiology 2 Treatment and prognosis 3 Examples 4 References 5 External links

[edit] Pathophysiology

The difference between a normal immune response and a type I hypersensitive response is that in the latter plasma cells secrete IgE. This class of antibodies binds to Fc receptors on the surface of tissue mast cells and blood basophils.^[2] Mast cells and basophils coated by IgE are "sensitized." Later exposure to the same allergen, cross-links the bound IgE on sensitized cells resulting in degranulation and the secretion of pharmacologically active mediators such as histamine, leukotriene (LTC4 and LTD4), and prostaglandin that act on the surrounding tissues. The principal effects of these products are vasodilation and smooth-muscle contraction.

Overview of mediators released by mast cells in type 1 hypersensitivity, and their actions:

Vasodilation and increased permeability	Histamine PAF Leukotriene C4, D4 and E4 Prostaglandin D2 Neutral proteases
Smooth muscle spasm	Histamine PAF Leukotriene C4, D4 and E4 Prostaglandin
Leukocyte extravasation	Cytokines (e.g. chemokines and TNF Leukotriene B4 Chemotactic factors for neutrophils and eosinophils
Unless else specified in boxes, then ref is: [3]

The reaction may be either local or systemic. Symptoms vary from mild irritation to sudden death from anaphylactic shock.

[edit] Treatment and prognosis

Treatment usually involves epinephrine, antihistamines, and corticosteroids. If the entire body gets involved, then anaphylaxis can take place; an acute, systemic reaction that can prove fatal.

[edit] Examples

Some examples:

• Allergic asthma
• Allergic conjunctivitis
• Allergic rhinitis ("hay fever")
• Anaphylaxis
• Angioedema
• Urticaria (hives)
• Eosinophilia
• Penicillin allergy
• Cephalosporin allergy
• Food allergy

[edit] References

[edit] External links

• Type I hypersensitivity (Flash Animation)

v • d • e Immune disorders: hypersensitivity and autoimmune diseases Type I/allergy/atopy (IgE) Foreign Atopic dermatitis · Allergic urticaria · Hay fever · Allergic asthma · Anaphylaxis · Food allergy (Milk, Egg, Peanut, Tree nut, Seafood, Soy, Wheat), Penicillin allergy Autoimmune none Type II/ADCC (IgM, IgG) Foreign Pernicious anemia · Hemolytic disease of the newborn Autoimmune Cytotoxic Autoimmune hemolytic anemia · Idiopathic thrombocytopenic purpura  · Bullous pemphigoid  · Pemphigus vulgaris · Rheumatic fever · Goodpasture's syndrome "Type 5"/receptor Graves' disease · Myasthenia gravis Type III (Immune complex) Foreign Henoch-Schönlein purpura · Hypersensitivity vasculitis · Reactive arthritis · Rheumatoid arthritis · Farmer's lung · Post-streptococcal glomerulonephritis · Serum sickness · Arthus reaction Autoimmune Systemic lupus erythematosus · Subacute bacterial endocarditis Type IV/cell-mediated (T-cells) Foreign Contact dermatitis · Mantoux test Autoimmune Diabetes mellitus type 1 · Hashimoto's thyroiditis · Guillain–Barré syndrome  · Multiple sclerosis  · Coeliac disease · Giant cell arteritis GVHD Transfusion-associated graft versus host disease Unknown/ multiple Foreign Hypersensitivity pneumonitis (Allergic bronchopulmonary aspergillosis) · Transplant rejection · Latex allergy (I+IV) Autoimmune Sjögren's syndrome · Autoimmune hepatitis · Autoimmune polyendocrine syndrome (APS1, APS2) · Autoimmune adrenalitis lymphocyte navs: cells/physio, immunodeficiency/immunoproliferative immunoglobulin/neoplasia, proc