Allergies and antihistamine Flashcards
What is an allergy?
Hypersensitive reactions which occur on exposure to otherwise harmless substances in the environment as a result of sensitisation
What is the role of the innate system in an allergic reaction?
its responsible for catalyzing the sensitization process which leads to allergic reactions.
Allergic individuals are genetically predisposed so that they?
overproduce T helper 2 cytokines and have insufficient T helper 1 response. The result of this imbalance is the production of antibody E against normally harmless environmental substances through sensitization.
What is the role of IgE?
It alerts other immune cells such as basophils in the blood and mast cells in the skin that they should be ready to destroy pathogen. Also triggers memory T cells which react quicker to future recognition of same antigen
What is type I hypersensitivity?
An allergic reaction induced by specific antigens called allergens when they allergy is provoked by re exposure to the same antigen either by contact, inhalation or injection. It’s mediated by specific IgE antibodies and produced by cellular release of histamine and other vasoactive mediators causing an immediate local or systemic reaction
What happens in type II hypersensitivity?
IgG antibody produced during immune response recognises and binds to antigen which can be intrinsic or extrinsic. Natural killer cells, polymorphonuclear cells, eosinophils and macrophages then bind via Fc receptors and cause damage to cell
What happens during type III hypersensitivity?
involves mostly antibodies forming immune complexes with antigen. Soluble immune complexes form in the circulation and deposit in various tissues where they may trigger complement activation. They then attach to RBCs, leave circulation and trigger inflammation in tissues spaces or are phagocytosed by macrophages, release cytokines and activate B and T cells. IgG, IgA, IgM and IgE all form complexes with antigen.
What happens during type IV hypersensitivity?
It’s a cell mediated hypersensitivity, particularly T cells and macrophages. Standard reaction is the delayed type hypersensitivity reaction in which activation of T cells around the site of antigen entry leads to T cell cytotoxicity and activation of macrophages causing tissue damage
What are the events that lead to the development of immediate hypersensitivity reactions? (type I)
production of IgE antibodies in response to antigen binding to the Fc receptors of mast cells, cross linking of the bound IgE by reintroduced antigen and release of mast cell mediators
What are some common allergens?
pollen, certain foods, insect venom, drugs, animal dander
Who would be called atopic and what do their mast cells look like?
Atopic people are those who produce IgE in response to an antigen. Their mast cells are coated with IgE antibody specific for the antigen of which the person is allergic.
What are the most important mediators produced by mast cells where are they released from?
released from their cytoplasmic granules and cytokines, include: vasoactive amines and proteases
What effect does histamine have?
it causes dilation of small blood vessels, increases vascular permeability and stimulates transient contraction of smooth muscles
How long does it take for type IV hypersensitivity to develop?
12+ hours
What is atopic dermatitis?
a chronic inflammatory skin disorder which in young children presents as rashes on face, neck, cheeks and scalp and in other children and adults eczema may appear or forearm, inner elbows and behind the knees
