Microbiology - Disorders of the Immune System - Quick Guides | Microbiology

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Study GuideMicrobiology–Disorders of the Immune System1.Hypersensitivity ReactionsNot all immune system activity is helpful. In some cases, immune responses themselves causedisease. These conditions are calledhypersensitivity reactions—states in which the immunesystem reactstoo strongly or inappropriately. Hypersensitivities may be caused byantibodiesorimmune cells, and they can lead to tissue injury or even death. Some immune disorders also involveimmunodeficiency, where parts of the immune system fail to function properly.1.1When Protection Turns HarmfulUnder normal conditions, the immune system protects the body from microorganisms and otherforeign substances. However, if the immune response becomesexcessive or misdirected, ahypersensitivity reaction occurs.•Damage usually happensafter antigens interactwith:oAntibodies, oroSensitizedT-lymphocytes•Thetype of immune component involveddetermines the nature and timing of the reaction.1.2Two Major Types of HypersensitivityHypersensitivity reactions are grouped intoimmediateanddelayedforms.Immediate Hypersensitivity•Involvesantibodies•Developswithin minutes•Includes:oAnaphylaxisoAllergic reactionsoCytotoxic reactionsoImmune complex reactions

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Study GuideDelayed Hypersensitivity•Involvessensitized T-lymphocytes•Takes24 hours or moreto develop•Includes:oContact dermatitisoInfection-related allergiesImmediate Hypersensitivity ReactionsImmediate hypersensitivity depends on:•Thetype of antigen•How often and how it enters the body•Theclass of antibodyinvolvedThe first exposure to an antigen is called thesensitizing dose.This is followed by alatent period, during which antibodies are formed.A later exposure to the same antigen, called theeliciting (or shocking) dose, triggers the reactionand causes tissue damage.1.3AllergensAntigens that trigger immediate hypersensitivity are calledallergens, especially when they causelocalized reactions.Common allergens include:•Foods•Pollen•Feathers•Animal dander•Dust•Bee and wasp venoms•Animal sera•Some drugs (e.g., penicillin, acting as ahaptenwhen bound to proteins)

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Study Guide1.4Anaphylaxis (Type I Hypersensitivity)Anaphylaxisis a severe, whole-body immediate hypersensitivity reaction, also calledanaphylacticshock.Figure 1The process of anaphylaxis. (a) Allergens stimulate the production IgE antibodies,which (b) fix themselves to the surfaces of mast cells. (c) On second exposure to theallergens, a reaction occurs on the mast cell surface, and (d) the cellular granules releasehistamine and other stimulators of smooth muscle contraction.

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