Chapter 20: Allergy Hypersensitivity Reactions These reactions are unwanted or uncontrolled immune responses to a particular antigen which can result in tissue damage or disease. These antigens can be either against 1) self antigens (and would cause autoimmunity), 2) pathogens, or 3) environmental antigens. There are 4 types on hypersensitivity responses, each classified by their mechanism of action and the type of immune response that is stimulated: Type I hypersensitivity response (immediate hypersensitivity) Type II hypersensitivity response (antibody-mediated disease) Type III hypersensitivity response (immune complex-mediated disease) Type IV hypersensitivity response (T cell-mediated delayed hypersensitivity response) In this chapter, our focus will be on the type I hypersensitivity responses and in Chapter 19, we will discuss the remaining hypersensitivity responses.The Allergic Response This response requires a sensitization phase and an elicitation phase and is characterized by vascular and smooth muscle changes. Let’s take a closer look… Abbas, Lichtman and Pillai8_Figure 20-1; p. 418The Cells of the Allergic Response Please note: the location of allergen entry into the body will play a significant role on the location and type of allergic response. Please see Table 20-1 on p. 420 and Table 20-2 on p. 421 (you are required to know the location of these cells, as well as their chemical mediators and corresponding functions) Mast cells Basophils Eosinophils Abbas, Lichtman and Pillai8_Figure 20-2; p.421The Fc Receptor (FcεR) Mast Cell Activation Abbas, Lichtman and Pillai8_Figure 20-3; p.422 Abbas, Lichtman and Pillai8_Figure 20-4 C-F; p.423What happens once a mast cell is bound by allergen? A lot! Abbas, Lichtman and Pillai8_Figure 20-5; p.424Functions of the Chemical Mediators Histamine: Prostaglandins: Leukotrienes: Abbas, Lichtman and Pillai8_Figure 20-6; p.426Cytokines: Why do we still need eosinophils? The Immediate and Late Phase Reactions Abbas, Lichtman and Pillai8_Figure 20-7; p.428 Abbas, Lichtman and Pillai8_Figure 20-11; p.434The immediate reaction The late-phase reaction Abbas, Lichtman and Pillai8_Figure 20-8; p.429The Hygiene Hypothesis Essentially, early exposure to microbes decreases the chance of developing allergies. This is evidenced by: - Children with multiple siblings have less allergies - Children in daycare have less allergies - Individuals who grow up on farms have less allergies Anaphylaxis Asthma Abbas, Lichtman and Pillai8_Figure 20-9; p.432Causes and treatments of asthma Abbas, Lichtman and Pillai8_Figure 20-10; p.433Other Allergic Reactions Allergic rhinitis – Food allergies – Urticaria and atopic dermatitis
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