Allergic reactions

Allergic reactions

Type-I hypersensitivity

Multiple Choice

Which of the following describes immunodeficiency?

• Immune cells attacking self cells

• Immune cells attacking non-self cells

• The failure of the immune system to function correctly, or at all

• The immune system producing an undesirable response

Vocabulary

• Allergen - an antigen that causes an allergic response

• Anaphylaxis - a severe allergic reaction that can cause death

• Mast cells - present in most tissues and produce histamine

• Immunoglobulin E - a type of antibody produced in an allergic response

Type-I hypersensitivity (allergic response)

• Type-I hypersensitivity is an immediate response to an allergen

• This is a reaction, often an overreaction, to an antigen that would otherwise be harmless

• Any antigen that causes this kind of response is an allergen

• Typically, allergens include pollen, fur, dust, foods including peanuts, and latex

Reaction to allergens

• Allergen triggers plasma cells to produce IgE antibodies

• IgE binds to mast cells

• On a subsequent exposure to the same allergen, the allergen binds to the gap between two antibodies on the mast cell

• This triggers mast cells to produce histamine

Histamine's effect

• Dilation of blood vessels (vasodilation)

• Increased permeability to immune cells and molecules

• Decreases blood pressure

• Contracts smooth muscle lining the airways, making breathing more difficult

• Activation of fluid-secreting cells (runny nose and eyes) to expel the allergen

Treatments

• Antihistamines bind to the gap between two antibodies on the mast cell, stopping histamine from doing the sam

• Cortisone can be used to suppress the immune response in general

• If the reaction is severe (anaphylaxis) an adrenaline shot is needed to constrict the blood vessels (decrease swelling), relax airway muscles, and increase the heartbeat to prevent cardiac damage

• Desensitisation - receive small doses of allergen to produce IgG antibodies (involved in humoral response). If IgG react to allergen before IgE binds to it, the allergic response is avoided. Patient receives larger doses over time, and becomes less sensitive. Also called allergen immunotherapy.

Multiple Choice

What type of antibodies do plasma cells produce in response to an antigen?

• IgM

• IgG

• IgE

• IgA

• IgD

Multiple Choice

Which of these does histamine NOT do?

• Increase permeability of vessels

• Vasoconstriction

• Decrease blood pressure

• Contraction of smooth muscles of the airway

• Activate fluid-secreting cells

Open Ended

List 3 common allergens.

Multiple Choice

Where does an allergen bind to a mast cell?

• On the cell membrane

• A receptor protein

• In the gap between two IgE antibodies

• In the cytoplasm

Multiple Choice

What triggers a mast cell to release histamine in an allergic response?

• The IgE antibodies binding to the mast cell membrane

• The allergens binding to the gap between two IgE antibodies on the mast cell

Open Ended

Beginning from the first exposure, describe how a type-I hypersensitivity reaction occurs to pollen.