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Type II Hypersensitivity: Antibody-mediated cytotoxicity Results when Ig or IgM bind to cell surface Ag’s –Activating Complement –Binding Fc receptors.

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Presentation on theme: "Type II Hypersensitivity: Antibody-mediated cytotoxicity Results when Ig or IgM bind to cell surface Ag’s –Activating Complement –Binding Fc receptors."— Presentation transcript:

1 Type II Hypersensitivity: Antibody-mediated cytotoxicity Results when Ig or IgM bind to cell surface Ag’s –Activating Complement –Binding Fc receptors on Tc cells promoting ADCC Both processes result in lysis of the Ab-coated cell Clinical examples of Type II responses include: –Certain autoimmune diseases where Ab’s produced vs membrane Ag’s Grave’s Disease – Ab’s produced vs thyroid hormone receptor Myasthenia Gravis – Ab’s produced vs acetylcholine recpetors Autoimmune hemolytic anemia – Ab’s produced vs RBC membrane Ag’s –Hemolytic Disease of the Newborn –Hyperacute graft rejection Blood Transfusion rxns Graft rejection

2 Type II Hypersensitivity: Transfusion reactions Produced by mismatched blood types –Destroys foreign RBC by complement- mediated lysis triggered by IgG Produces fever, intravascular clots, lower back pain, Hgb in urine –Free Hgb produced has 2 fates: passes to the kidneys – hemoglobinuria Breaks down to bilirubin..can be toxic

3 Type II Hypersensitivity: Hemolytic Disease of the Newborn Occurs via maternal IgG Ab’s crossing the placenta In severe cases causes erythroblastosis fetalis –Most commonly develops in Rh- mother with Rh+ fetus –Exposure to Rh+ fetal RBC’s stimualtes prod of memory/plasma –Activation of memory cells in subsequent pregnancy stim IgG Ab’s which can cross the placenta –mild-severe hemolytic anemia ensues along with bilirubin which affects the brain/CNS Treatment centers on anti-Rh antibodies (Rhogam) Mothers can be tested for anti-Rh antibodies to check for a rise in titre Isolated fetal RBC’s can be checked for anti-Rh IgG w/ Coombs test

4 Hemolytic Disease of the Newborn

5 Type II Hypersensitivity: Drug-induced hemolytic anemia Drugs such as aspirin and antibiotics can bind to the surfaces of RBC’s These interactions act similar to hapten-carrier conj. Such complexes can trigger Ab-mediated cell lysis by complement activation

6 Type III Hypersensitivity: Immune Complex-mediated cytotoxicity Caused by immune complex deposition in tissues –Small amts cleared by phagocytic cells –Activates complement which attracts neutrophils and stim Mast cell degranulation –Depending on location, rxn can be localized or systemic Most damage stems from activity of Neutrophils –Immune complexes can adhere to tissue making it difficult for Neutrophils to phagocytize –Neutrophils continue releasing lytic enzymes, etc.

7 Type III Hypersensitivity: Localized reactions Arthus rxns: –Exposure to an Ag for which there already is a high [c] of Ab –Produces edema/erythema from damage to bv and tiss Insect bites Inhalation of bacteria, fungi, dried fecal matter

8 Type III Hypersensitivity: Systemic (generalized) reactions Produced when large amounts of Ag enter the bloodstream –The sites of deposition vary; usually in tissues where plasma is filtered –Esp. in kidneys, blood vessels, and joints Can cause tissue damaging rxns : Serum sickness Autoimmune diseases Drug reactions Infectious diseases

9 Type IV Hypersensitivity: Delayed-Type Hypersensitivity Occurs 48-72 hrs after Ag contact and is mediated by Ag-specific T H 1 cells and activated MØ TH1 cells secrete: –IFN-γ activates MØ –TNF-α and β upregulate CAM’s on local b.v’s –Il-3 and GM-CSF stim bone marrow monocyte output Initial contact with Ag (sensitization) may induce memory TH1 cells without symptoms

10 Phases of the DTH Response Sensitization – TH1 cells triggered by contact with APC Effector response – produces huge influx of activated MØ –Activated MØ is more efficient at antigen-presentation –Release of lytic enzymes lead to non-specific destruction of cells –Works well vs intra-cellular pathogens –If pathogen/particle lingers -> can lead to granuloma formation Ex: Mycobacterial pathogens in TB and Leprosy

11 DTH Response Cytokines released include: TNF-β, GM-CSF, and IFN – γ

12 DTH Response Type IV rxns marked by time delay and recruitment of MØ instead of Neut’s and Eosino’s

13 Contact Dermatitis Produced by a variety of substances Mostly small molecules attach to a protein in the skin The Ag-protein complex is processed and presented  sensitize TH1 cells Subsequent exposure activates TH1 cells  48-72 hrs later MØ infiltrate Activation of MØ causes the inflammation that characterizes the disorder


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