DiseasesHypersensitivity- Types

Types of Type 1 hypersensitivity

• Type I Reactions Can Be – Systemic – Localized

SYSTEMIC ANAPHYLAXIS

• occurs within minutes after the allergen is introduced in blood (bee sting or through gut)

• Symptoms range from mild urticaria (hives) to shock-like symptom i.e.

• anaphylaxis may become fatal e.g.– respiration may become labored– blood pressure may drop– Airway constriction– Swelling of epigottis– Difficulty in breathing

• Usually against foods such as peanuts or bee sting

Some historians claim that Egypt's first pharaoh, Menes, was killed by a wasp's sting

Treatment

• Epinephrine is the drug of choice for systemic anaphylactic reactions:– relaxing the smooth muscles and reducing

vascular permeability– improves cardiac output

SYSTEMIC ANAPHYLAXIS

• Urticaria may be:– Acute (type I)– chronic (type II)

• Might be caused by:– venom from bee, wasp,

hornet, and ant stings; – drugs, such as penicillin,

insulin, and antitoxins; – seafood and nuts

• If not treated quickly, these reactions can be fatal

Interestingly Some IgE mediated anaphylaxis in response

to insect venom, drugs or foods are not associated with atopy

LOCALIZED ANAPHYLAXIS (ATOPY)

• Tendency to manifest localized anaphylactic reactions is inherited and is called atopy

• In localized anaphylaxis, the reaction is limited to a specific target tissue or organ- epithelial surfaces at the site of allergen entry

• Atopic allergies, which afflict at least 20% of the population in developed countries

• include a wide range of IgE-mediated disorders– including allergic rhinitis (hay fever), – asthma, – Atopic dermatitis (eczema)– and food allergies

Late-Phase Reactions Induce LocalizedInflammatory Reactions

• As a type I hypersensitive reaction begins to subside, mediators released during the course of the reaction often induce localized inflammation called the late-phase reaction

• The late-phase reaction begins to develop 4–6 h after the initial type I reaction and persists for 1–2 days

• The reaction is characterized by infiltration of neutrophils, eosinophils, macrophages, lymphocytes, and basophils

• The localized late-phase response also may be mediated partly by cytokines released from mast cells

Mediators of early and late phase responses of Type 1 hypersensitivity

Allergy- Treatments

Type I Hypersensitivities Can BeControlled Medically

• to avoid contact with known allergens

• Often the removal of house pets,

• dust-control measures, • or avoidance of

offending foods can eliminate a type I response

Avoid contact . Removal of house pets, dust-control measures, or avoidance of offending foods . Elimination of inhalant allergens –pollens is a physical impossibility

Immunotherapy• repeated injections of

increasing doses of allergens (hyposensitization) has been known for some time to reduce the severity of type I reactions

• shift toward IgG production

• to induce T-cell– mediated suppression

• the use of humanized monoclonal anti-IgE