Introduction to Lab Ex. 24: Hypersensitivity

• Response to antigens (allergens) leading to damage

• Require sensitizing dose(s)

Introduction to Lab Ex. 24: Hypersensitivity

Hypersensitivity is thus an exaggerated response of the immune system.

There are 4 types of hypersensitivity reactions:- Type 1: IgE mediated Anaphylaxis reactions- Type 2: Cytotoxic reactions (IgG/IgM)- Type 3: Immune complex reactions (IgG)- Type 4: TD cell mediated reactions

Types 1, 2, 3 are antibody mediated and are of the Immediate typeType 4 is cell (TD)mediated and is of the Delayed type

• Involve IgE antibodies, mast cells, basophils

• Localized: Hives or asthma from contact or inhaled antigens

• Systemic: Shock from ingested or injected antigens

Type I (Anaphylactic) Reactions

Figure 19.1a

On first exposure (sensitizing) to allergen IgE antibodies are formed.

IgE antibodies circulate through the body and bind by their Fc portions to receptors on the surface of mast cells andbasophils.

On reexposure to the same antigen, binding of the antigen to IgEon the surface of mast cells and basophils could lead tocrossbridging

Crossbridging stimulates the degranulation of the mast cells.

Mast cells:- found in connective tissue of the skin, respiratory tract

and in surrounding blood vessels- contain granules with chemicals (mediators)- have many receptors for Fc portion of IgE- cross bridging causes degranulation

Basophils:- circulate in blood stream- contain granules with chemicals (mediators)

Mediators include:- histamine- leukotrienes- prostaglandins

Histamine effects:- increase permeability of capillaries- cause swelling and redness- increase mucous secretion- cause smooth muscle contraction

Leukotrienes effects:- cause prolonged smooth muscle contraction(spasms of the bronchial tubes)

Prostaglandin effects:- cause mucous secretion- cause smooth muscle contraction (respiratory system)

Results of allergic reaction: inflammation (neutrophils, eosinophils)- distension of capillaries, swelling, mucus secretion,

smooth muscle contractions

• Skin testing

RAST – to identify allergens

Type I (Anaphylactic) Reactions

Figure 19.3

Treatment/ therapy:- Antihistamine: block histamine binding sites in nose and

skin- Desensitization: stimulate IgG production to allergen

(allergy shots)- Cromolyn sodium: stabilizes mast cell membranes, thus

inhibiting histamine release in nasal tissues/bronchialmucus membranes

- Epinephrine: relaxes smooth muscles in lung; constrictsblood vessels (raises blood pressure); immediate action