Hypersensitivity Flashcards
What is hypersensitivity?
An over-reactive immune response occurs aka a harmful immune response that produce tissue injury and may cause serious disease
What are the 4 types of hypersensitivity?
Immediate hypersensitivity includes Types I, II and III and occurs within minutes to hours. Delayed hypersensitivity includes Type IV and occurs days after exposure
Describe Type I hypersensitivity
IgE-mediated, an example of type I hypersensitivity is a bee sting. Immediate, resulting usually within 20 minutes. Induced by allergens which create an allergic response. Allergies can be transferred to naïve animals and when activated can release mediators such as histamine, prostaglandins, TNF, IL-3, IL-4 and IL-5
Describe Type II hypersensitivity
IgG-mediated, results in red blood cells being killed and can affect infants. Types II and III have similar mechanisms, but different targets. Can be induced by IgG or IgM. Require the antigen to be on the cell surface to occur. These activate NK cells and recruit complement
Describe Type III hypersensitivity
Immune-complex mediated, immediate and require antibody for induction. Can result from an insect bite and is usually compared to Type I. It relies on soluble antigens
Describe Type IV hypersensitivity
Cell-mediated, delayed and no antibody is required. Can be deficient and can die from infection to the allergy. Cutaneous and is mostly due to contact, proteins are haptenated and alternate proteins are produced. Type IV systemic reaction is delayed and associated with the TB vaccine. Not associated with an allergic reaction. Inductor cells are CD4+ T cells but they can also be CD8+, result in a Th1 response. Requires no antibody or antigen, and rely on proteins alone
What antigens are involved in Type I hypersensitivity?
Evoke Th2 and IgE responses and are known as allergens, occurs due to a combination of antigen and genetics, with the production of IL-4
What antigens are involved in Type II hypersensitivity?
Present on the cell surface and can sometimes be classified as drugs or blood groups. Blood group antigens view a foetus as a parasite and see it as foreign
What antigens are involved in Type III hypersensitivity?
Soluble in high concentration and can form immune complexes
What antigens are involved in Type IV hypersensitivity?
May alter self-antigens, resulting in allergic reactions to things such as poison oak, poison ivy and metal
What is a P-K reaction?
First passive cutaneous anaphylaxis wheal and flare test, occur in atopic serums where allergens are present. Serum not atopic but an allergen present; no P-K reaction.
What is an antigen?
Promotes Th2 priming and IgE production. All antigens must be proteins. Allergens are also often proteases (house dust mite, cat fur, dog fur) so must be enzymatically active. Must have a low dose and a low molecular weight to activate IL-4 producing T cells and diffuse from particle into mucus. Must also be highly soluble as to be able to be eluted from the particle. Also be stable in order to survive desiccation, MHC class II binding peptides required for T cell priming
How is IgE produced?
Th2 response and binds to high affinity receptor FcRI on mast cells, basophils and eosinophils. Need to be cross-linked and bound back to the antigen. Triggers degranulation of these cells and releases mediators and cytokines.
