Objectives
- to appreciate the cuases and prodisposing factors in allergy
- to know the sequence of events leading to an allergic reponse
- TO understand thebassi of immunotherapy / desensitisatio therapy
- To be able to define the four main types of hypersensetivity
What is allergy
Inappropriate immune response by by genetically predisposed host to nonpathogenic antigens
Allergy is a type i hypersensitivity, but is often associated with a type IV late phase
Allergy requires 3 components
- allergen
- Serum factor (IgE)
- Tissue factor (Mast cells)
Prausnitz-kustner test
Allergens
Allergens are little molecules that can induce an allergic response
Common allergen properties are:
- Protein often with carbohydrate side chains
- Enzymatically active
- Low dose
- Low molecule weight
- Highly soluble
- Stable
- Contains peptide that bind to MHC-II
Types of hypersensetivity
Type I
Type I is IgE mediated
Type II
Type III
Type IV
Type IV is T Cell mediated
Mechanism of development of allergy
Immune response handshake occurs between Allergen and Bcell-tcell (in the classic fashion). IgE antibodies are made.
Mast cell binfs to IgE antibody.
upon reexposure to allergen mast cells degranulate.
Tcell then migrate to site of exposure
Hygiene hypothesis
First world countries have higher incidence of allergies and early infections/ bowel colonisation protective
Idea is dirty kids have more exposure to actual antigens to react to and therefore have more calibrated immune system
Genetic link to allergies
IL-4 IL-4 receptor a chain High affinity IgE receptors B gene MHC class II genes
Allergen Specific Immunotherapy (SIT)
In this you are able to alter T cells Th2 to a Th1 response High dose antigen may inactivate B cells and induce production of T regulatory cells High dose antigen can inactivate IgE producing B cells can occur within hours