Hypersensitivity

Question 1

What does the pneumonic ACID stand for?

Answer 1

• A= anaphylatic and Atopic
• C= cytotoxic (antibody mediated)
• I= immune complex
• D= delayed (cell mediated)

Question 2

Type I

• define anaphylactic and atopic
• describe mech of type I
• why does a delyaed response follow?

Answer 2

Type I

• define anaphylactic and atopic
  
  • free antigens that cross link IgE on presensitized mast cells and basophils
  • Thus triggering immediated response of vasoactive amines that act at postcapillary venuls (histamine)
• describe mech of type I
  
  • Rxn develops after antigen exposure due to predeveloped antibodies that are present.
• Why does a delayed response follow?
  
  • delayed response due to the production of arachidonic acid metabolites (leukotrienes)

Question 3

Type II

• What are the antibodies that cause it to be considered cytotoxic
• define 3 mechanisms that define type II hypersensititivity

Answer 3

Type II

• What are the antibodies that cause it to be considered cytotoxic
  
  • IgM, IgG bind to fixed antigen on ‘enemy’ cell, leading to cellular destruction
• Define 3 mechanisms that define type II hypersensititivity
  
  • ​Opsonization: leading to phagocytosis or complement activation
  • Cell mediated lysis
  • Antibody depenedent cell mediated cytotoxicity (usually due to NK cells or macrophages)

Question 4

What is the test done to determine type II hypersensitivity?

• Describe the opposite test as well

Answer 4

• Direct coombs: detects antibodies that directly adhere to pts RBC
  
  • (e.g. test an Rh positive infant of an Rh neg mother)
• Indirect coombs: detects antibodies that can adhere to other RBCs (what is found in teh serum)
  
  • (eg. test an Rh neg woman for Rh pos antibodies)

Question 5

Type III

• Define type III hypersensitivity
• define serum sickness
• define arthus rxn

Answer 5

Type III

• Define type III hypersensitivity
  
  • antigen-antibody (IgG) activates complement
  • complement attracts neutrophils
  • neutrophils release lysomoal enzymes
• Define serum sickness
  
  • (takes 5 days) antibodies to the foreign proteins are produced
  • Immune complexes form and are depositied in membranes where they fix complement
  • more common than arthus rxn
• Define arthus rxn
  
  • a local subacute antibody-mediated rxn
  • intradermal injection of antigen induces anitbodies (which form antigen-antibody complexes in the skin)
  • characterized by edema, necrosis, and activation of complement

Question 6

Type III

• General what is it: 3 things that compose it
• serum sickness is caused by what
• how do you test for arthus rxn

Answer 6

Type III

• General what is it: 3 things that compose it
  
  • antigen-antibody-complement
• serum sickness is caused by what
  
  • drugs (not serum) acting as haptens,
  • fever, urticaria, arthralgias, proteinuria, lymphadenopathy
  • 5-10 days after exposure
• how do you test for arthus rxn
  
  • Immunofluorescent staining

Question 7

Type IV

• What is it
• define mechanims
• what are the 4 T’s
• how do you test for it

Answer 7

Type IV

• What is it
  
  • delayed tcell mediated type sensitized
• define mechanims
  
  • T lymphocytes encounter antigen adn then release lymphokines (leads to macrophage activation, no antibody involvement)
• what are the 4 T’s
  
  • T lymphocytes, Transplant rejections, TB skin test, Touching (contact dermatitis)
• Test
  
  • patch test, PPD

Question 8

Define the rxn and presentation for the following diseases:

• Anaphylaxis (e.g. bee sting, some food/drug allergies)
• Allergic and atopic disorders (e.g. rhinitis, hay fever, eczema, hives, asthma)

Answer 8

• Rxn: type I hypersensitivity
• Presentation: immediate, anaphylactic, atopic

Question 9

Define the rxn and presentation for the following diseases:

• Autoimmune hemolytic anemia
• Pernicious anemia
• Idiopathic thrombocytopenic purpura
• Erythroblastosis fetalis
• Acute hemolytic transfusino rxn
• Rheumatic fever
• Goodpasture syndrome
• Bullous pemphigoid
• Pemphigus vulgaris

Answer 9

• rxn: Type II hypersensitivity
• Presentation: disease tends to be specific to tissue or site where antigen is found

Question 10

Define the rxn and presentation for the following diseases:

• SLE
• Polyarteritis nodosa
• Poststreptococcal glomerulonephritis
• Serum sickness
• Arthus rxn (e.g. swelling and inflammation following tetanus vaccine)

Answer 10

• Rxn: Type III hypersenstivity
• Presentation: Can be assocaited with vasculitis and systemic manifestations

Question 11

Define the rxn and presentation for the following diseases:

• Multiple sclerosis
• Guillain-Barre syndrome
• Graft-vs-host disease
• PPD (test for M. tuberculosis)
  
  • Contact dermatitis (e.g. poison ivy, nickel allergy)

Answer 11

• Rxn: Type IV hypersensitivity
• Presentation: response is delayed and does not invovled antibodies!!! (I-III do involve antibodies)