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General Pathology VDMP832 > Abnormal Immunity - Hypersensitivity > Flashcards

Abnormal Immunity - Hypersensitivity Flashcards

1
Q

Immunopathology

A
  • Diseases characterized by abnormal or inappropriate immune responses
  • Major Conditions include:
    • Hypersinsitivity reations
    • Immunodeficiency
    • Autoimmunity
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2
Q

Immunopathology:

Hypersensitivity Reactions

A
  • Most immune responses to antigens are advantageous to the host
  • Some immune responses can cause host injury
  • Host injury due to hypersensitivity reactions occurs by several main machanisms
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3
Q

Hypersensitivity Reactions:

A
  • There are 4 main immune mechanisms of hypersensitivity-induced injury
    • Type 1
    • Type 2
    • Type 3
    • Type 4
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4
Q

Hypersensitivty Reactions:

Type 1

A
  • An immediate response characterized by prominent vacoactive events and teh release of inflammatory mediators
  • Key features:
    • Antigens that induce IgE production
    • IgE-mediated mast cell degranulation
    • Vascular leakage and eosinophil infiltration
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5
Q

Type 1 Hypersensitivity:

Mechanism

A
  • Prior exposure to an antigen stimulates production of antigen-specific IgE
  • IgE binds to Fc receptors of mast cells and basophils
  • Subsequent antigen exposure results in crosslinking of IgE and cell degranulation
  • Vasoactive mediators are released into the surrounding tissues
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6
Q

Type 1 hypersensitivity:

Local Manifestation:

Ingested Allergens

A
  • Ingested allergens
    • common inciting allergens include:
      • milk, wheat products, eggs, fish, alfalfa
    • Gastrointestinal signs range from mild, to severe with bloody diarrhea and vomiting.
    • Approximately half of food allergies have skin anifestations
      • erytherma, pruitis, urticaria
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7
Q

Type 1 hypersensitivity:

Local Manifestations:

Inhaled allergens

A
  • Common allergens include:
    • molds, pollens, house dust, fabrics
  • Responses to most inhaled allergens are manifested in the skin
    • atopic dermatitis:
      • lesions range from acute erytherma to chronic hyperpigmentation and pyodermas
      • Pruritis is a major feature
  • Responses to some inhaled allergens are manifested in the respiratory tract
    • nasolacrimal urticaria
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8
Q

Type 1 Hypersensitivity:

Local Manifestations

Cutaneous Allergens

A
  • Common allergens include:
    • insect bite, mites, fly larvae
  • Most ingested or inhaled allergens result in skin responses:
    • atopic dermatitis
  • Locally applied allergens can also result in hypersentitivity dermatitis
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9
Q

Type 1 Hypersensitivity:

Systemic manifestations:

A
  • Anaphylaxis
  • Signs and lesions are usually typical of shock
  • Manifestations can include:
    • respiratory distress and pulmonary failure
    • Gastrointestinal dysfunction and liver failure
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10
Q

Hypersensitivity Reactions:

Type 2

A
  • Cytotoxicity induced by reactions against cell membrane antigens
  • Key features:
    • Antigens that induced IgG or IgM production against cell membrane antigens
    • Antibody-mediated activation of complement or leukocytes results in cell damage
  • End result is membrane damage and cell injury
  • Two different mechanisms damage the cells
    • complement-mediated
    • Leukocye-mediated
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11
Q

Type 2 Hypersensitivity:

Complement-mediated mechanism

A
  • Antibody binds a cell membrane or basement membrane antigen
  • Classical complement cascade is activated
  • Formation of the terminal membrane attack sequence and cell lysis
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12
Q

Type 2 Hypersensitivity:

Leukocyte-mediated mechanism

A
  • Antibody binds a cell membrane or basement membrane antigen
  • Leukocytes bind via their Fc receptors
  • Leukocyte products damage the membrane
    • lysosomal enzymes
    • Oxygen free radicals
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13
Q

Type 2 Hypersensitivity:

Manifestation:

Reaction against Erythrocytes

A
  • Transfusion reactions
  • neonatal isoerythorlysis
  • Autoimmune hemolytic anemia
  • Drug-induced hemolysis
  • Infectious agents

Notable clinical signs in most cases is hemolytic anemia

  • Pathologic features
    • icterus
    • Splenomegaly
    • Hemosiderosis of various tissues
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14
Q

Type 2 hypersensitivity:

Manifestations:

Reactions against leukocytes

A
  • Neonatal leukopenia
  • Agranulocytosis (acquired leikopenia)

There may be increased susceptibility to infection

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15
Q

Type 2 hypersenstivity:

Manifestations

Reactions against Platelets

A
  • Drugs
  • Infectious agents
  • Autoimmunity

Thrombocytopenia is the major finding

Pathologic findings are predominately multiple petechial to ecchymotic hemorrhage

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16
Q

Type 2 Hypersensitivty:

Manifestations:

Reactions agianst Basement membranes

A
  • Antibodies are directed against basement membranes
    • glomerular and epidermal basement membranes are common targets
  • Injury can be mediated by complement or leukocytes
17
Q

Hypersensitivity Reactions:

Type 3

A
  • Tissue damage induced by inflammatory responses to immune complexes
  • Key features:
    • Appropriate immune complexes
      • formed in slight antingen excess
    • Complement and leukocyte-induced tissue injury
    • Reactions can occur to localized or circulating immune complexes
18
Q

Type 3 Hypersenstivity:

Mechanisms:

Localized Hypersentitivity (arthus reaction)

A
  • Interstitial antigen and intravascular antibody meet and precipitate within vessel walls
  • Complement and leukocyets mediate vessel damage
  • There is vascular necrosis, hemorrhage, thrombosis, and local tissue damage
19
Q

Type 3 Hypersensitivity:

Mechanisms:

Systemic Hypersensitivity (serum sickness)

A
  • Soluble, circulating immune complexes can be deposited within vessels of multiple tissues
  • Complement and leukocytes induce vessel and tissue damage
20
Q

Type 3 Hypersensitivity:

Manifestations:

Vasculitis

A
  • Some degree of vasculitis occurs with al type 3 reactions
  • COmmonly affected tissues include:
    • kidney
    • Lungs
    • joints
    • Eyes
21
Q

Type 3 Hypersensitivity:

Manifestations:

Kidney

A
  • Immine complexes can be formed in many diseases, and can be deposited near glomerular basement membranes
  • Complement and leukocyte-mediated damage cause glomerulonephritis
22
Q

Type 3 Hypersentivity:

Manifestations:

Lungs

A
  • Deposition of immune complexes near alveolar and endothelial basement membranes
  • Complement and leukocyte-mediated damage cause alveolitis
23
Q

Type 3 Hypersensitivity:

Manifestations:

Joints

A
  • Immune complexes can be deposited in synovial membranes
  • Complement and leukocyte-mediated damage cause synovitis and arthritis
24
Q

Type 3 Hypersensitivity:

Manifestations:

Eyes

A
  • Immune complexes can be deposited in the uvea
    • this is common as sequella to canine andeovirus-1 infections
  • Complement and leukocyte-mediated damage cause anterior uveitis and corneal edema
25
Q

Hypersensitivity Reactions:

Type 4

A
  • Delayed hypersensitivity reactions mediated by antibody-independent immune responses
  • Key features:
    • Persistent antigen
    • T-lymphocyte proliferation and production of lymphokines
    • Macrophage proliferation and activation
26
Q

Type 4 Hypersenitivity:

Mechanisms

Tissues (delayed hypersensitivity)

A
  • Antigen persistence stimulates lymphocytes and macrophage infiltration to the site
    • vasodilation and increased vascular permeability are minor parts of the typical response
  • T-lymphocytes and macrophages proliferate locally and produce cytokines that mediate removal of the antigen and associated tissue damage
27
Q

Type 4 Hypersensitivity:

Mechanisms:

Cell-mediated cytotoxicity

A
  • Certain cell-associated antigens cause the generation of cytotoxic T-lymphocytes
    • often these are virus infected cells and tumor cells
  • Natural killer cells recognized abnormal membrane antigens
  • Cytotoxic T-lymphocytes and natural killer cells bind to and destroy the abnormal cells.
28
Q

Type 4 Hypersensitivity:

Manifestations:

Tuberculin Reaction

A
  • Intradermal injection of antigen in a sensitized animal causes local swelling and macrophage infiltration
  • This is used for diagnostic testing to a variety of agents
    • mycobacterium sp.
29
Q

Type 4 Hypersensitivity:

Manifestation:

Granulomatous Hypersensitivity

A
  • This is a combination of delayed hypersensitivity and granulomatous inflammation
    • antigen persistence is a characteristic of both
  • Lymphocytes and macrophages are prominent at the site
  • Common causes include:
    • systemic fungal infections
    • Mycobacgerial infections
30
Q

Type 4 Hypersenstivity:

Manifestations:

Contact Hypersensitivity

A
  • Dermal contact with certain antigens induces a cell-mediated delayed hypersensitivity
  • Cellular infiltrate is largely lymphocytic
  • Common causes:
    • plants such as poison ivy
    • Flea collars
    • wood preservatives and waxes
    • Paints, dyes, fabric chemicals

General Pathology VDMP832 (26 decks)

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