ALLERGOLOGY

The branch of medical science that

studies the causes and treatment of

allergies

Allergy• a disorder of the immune system often

also referred to as atopy

• occur to normally harmless environmental

substances known

as allergens

• allergy is one of four forms of hypersensitivity and is called type I (or immediate) hypersensitivity

• characterized by excessive activation of certain white blood cells called mast cells and basophils by a type of antibody known as IgE, resulting in an extreme inflammatory response

What is hypersensitivity?

• Abnormal sensitivity, a condition in which there is an exaggerated response by the body to the stimulus of a foreign agent. example: allergy

Comparison of hypersensitivity types

Type Alternative namesOften mentioned

disorders Mediators

I Allergy (immediate)

Atopy

IgEAnaphylaxisAsthma

IICytotoxic, antibody-dependent

Autoimmune hemolytic anemia IgM or IgGThrombocytopenia (Complement)Erythroblastosis fetalis  Goodpasture's syndrome  

IIIImmune complex disease

Serum sickness IgGArthus reaction (Complement)Systemic lupus erythematosus (SLE)  

IV

Delayed-type hypersensitivity (DTH), cell-mediated immune memory response, antibody-independent

Contact dermatitis

T-cells

Mantoux testChronic transplant rejection

Multiple sclerosis

V Autoimmune disease

Grave's disease IgM or IgGMyasthenia Gravis (Complement)Hashimoto's thyroiditis  Systemic lupus erythematosus  

Common Allergic Reaction• Hives• hay fever• Asthma• Food allergies• Reactions to the venom of stinging insects such as wasps and bees

Affected Organ Symptom

NoseNose Swelling of the nasal mucosa (allergic rhinitis)Swelling of the nasal mucosa (allergic rhinitis)

SinusesSinuses allergic sinusitisallergic sinusitis

EyesEyes redness and itching of the conjunctiva (allergic conjunctivitis)redness and itching of the conjunctiva (allergic conjunctivitis)

AirwaysAirways sneezing, coughing, and sometimes outright attacks of asthma sneezing, coughing, and sometimes outright attacks of asthma

EarsEarsfeeling of fullness, possibly pain, and impaired hearing due to the lack of feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainageeustachian tube drainage

SkinSkin rashes, such as hives (urticaria)rashes, such as hives (urticaria)

Gastrointestinal Gastrointestinal tracttract abdominal pain, vomiting and diarrheaabdominal pain, vomiting and diarrhea

Cause Risk factors for allergy can be placed in two

general categories, namely host and environmental factors.

• Host factor:– heredity, sex, race, and age

• Environmental factor:– alterations in exposure to infectious diseases during

early childhood, environmental pollution, allergen levels, and dietary changes

– Aside from these ambient allergens, allergic reactions can result from foods, insect stings, and reactions to medications like aspirin and antibiotics such as penicillin.

Treatment• Pharmacotherapy

– several antagonistic drugs are used to block the action of allergic mediators, or to prevent activation of cells and degranulation processes. These drugs help to alleviate the symptoms of allergy, and are imperative in the recovery of acute anaphylaxis, but play little role in chronic treatment of allergic disorders.

• Immunotherapy– Desensitization or hyposensitization is a treatment in

which the patient is gradually vaccinated.