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Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 1
Hypersensitivity
Altered immunologic response to an antigen that results in disease or damage to the host
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 2
Hypersensitivity (cont’d)
Allergy Deleterious effects of hypersensitivity to
environmental (exogenous) antigens Autoimmunity
Disturbance in the immunologic tolerance of self-antigens
Alloimmunity Immune reaction to tissues of another
individual
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 3
Hypersensitivity (cont’d)
Characterized by the immune mechanism: Type I
• IgE mediated Type II
• Tissue-specific reactions Type III
• Immune complex mediated Type IV
• Cell mediated
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 4
Hypersensitivity (cont’d)
Immediate hypersensitivity reactions Anaphylaxis Delayed hypersensitivity reactions
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 5
Type I Hypersensitivity
IgE mediated Against environmental antigens (allergens) IgE binds to Fc receptors on surface of
mast cells (cytotropic antibody) - “sensitized”
Histamine release H1 and H2 receptors Antihistamines
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 6
Type I Hypersensitivity (cont’d)
Manifestations: Itching Urticaria Conjunctivitis Rhinitis Hypotension Bronchospasm Dysrhythmias GI cramps and malabsorption
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 7
Type I Hypersensitivity (cont’d)
Genetic predisposition- atopic Tests:
Food challenges Skin tests Laboratory tests
Desensitization Cautiously
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 8
Type I Hypersensitivity (cont’d)
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 9
Type II Hypersensitivity
Tissue specific Specific cell or tissue (tissue-specific antigens)
is the target of an immune response
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 10
Type II Hypersensitivity (cont’d)
Five mechanisms: Cell is destroyed by antibodies and
complement Cell destruction through phagocytosis Soluble antigen may enter the circulation and
deposit on tissues; tissues destroyed by complement and neutrophil granules
Antibody-dependent cell-mediated cytotoxicity (ADCC)
Causes target cell malfunction (e.g., Graves)
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 11
Type III Hypersensitivity
Immune complex mediated Antigen-antibody complexes are formed in
the circulation and are later deposited in vessel walls or extravascular tissues
Not organ specific Serum sickness Raynaud phenomena Arthrus
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 12
Type IV Hypersensitivity
Does not involve antibody Cytotoxic T lymphocytes or lymphokine
producing Th1 cells Direct killing by Tc or recruitment of phagocytic
cells by Th1 cells Examples:
Acute graft rejection
Skin test for TB
Contact allergic reactions
Some autoimmune diseases
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 13
Allergy
Most common hypersensitivity and usually type I
Environmental antigens that cause atypical immunologic responses in genetically predisposed individuals Pollens, molds and fungi, foods, animals, etc.
Often allergen is contained within a particle too large to be phagocytosed or is protected by a nonallergenic coat
Bee stings
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 14
Autoimmunity
Breakdown of tolerance Body recognizes self-antigens as foreign Self-antigens not normally seen by the immune
system Infectious disease (e.g., rheumatic fever,
glomerulonephritis) Antigenic mimicry
Neoantigen Haptens become immunogenic when they bind
to host proteins
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 15
Autoimmune Examples
Systemic lupus erythematosus (SLE) Chronic multisystem inflammatory disease Autoantibodies against:
• Nucleic acids• Erythrocytes• Coagulation proteins• Phospholipids• Lymphocytes• Platelets, etc.
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 16
Autoimmune Examples (cont’d)
Systemic lupus erythematosus (SLE) Deposition of circulating immune complexes
containing antibody against host DNA More common in females
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 17
Systemic Lupus Erythematosus
Clinical manifestations: Arthralgias or arthritis (90% of individuals) Vasculitis and rash (70%-80%) Renal disease (40%-50%) Hematologic changes (50%) Cardiovascular disease (30%-50%)
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 18
Systemic Lupus Erythematosus (cont’d)
Eleven common findings:
Serial or simultaneous presence of at least four indicates SLE
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 19
Alloimmunity
Immune system reacts with antigens on the tissue of other genetically dissimilar members of the same species Transplant rejection and transfusion reactions:
• Major histocompatibility complex (MHC)• Human leukocyte antigens (HLC)
Transfusion reactions• ABO blood groups
Rh incompatibility• Hemolytic disease of newborn
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 20
Graft Rejection
Transplant rejection is classified according to time Hyperacute
• Immediate and rare• Preexisting antibody to the antigens of the graft
Acute• Cell-mediated immune response against unmatched
HLA antigens
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 21
Graft Rejection (cont’d)
Transplant rejection is classified according to time Chronic
• Months or years• Inflammatory damage to endothelial cells of vessels
as a result of a weak cell-mediated reaction against minor HLA antigens
Mosby items and derived items © 2012 Mosby, Inc., an imprint of Elsevier Inc. 22
Graft-Versus-Host Disease (GVHD)
Immunocompromised individuals are at risk for CVHD T cells in the graft are mature and capable of
cell-mediated destruction tissues within the recipient
Not a problem if patient is immunocompetent