Hypersensitivity Flashcards
What is a Type I hypersensitivity reaction?
Anaphylatctic & atopic
What happens in Type I hypersensitivity rxns?
Free Ag cross-links IgE on presensitized mast cells & basophils, triggering release of vasoactive amines that act at postcapillary venules
What is the onset of a Type I hypersensitivity rxn?
Rxn develops rapidly after Ag exposure b/c of preformed Ab
What is the test for Type I hypersensitivity rxn?
Skin test for specific IgE
What is a Type II hypersensitivity rxn?
Cytotoxic (Ab mediated)
What happens in a Type II hypersensitivity rxn?
IgM, IgG bind to fixed Ag on “enemy” cell l/t cellular destruction
What are the 3 mech of Type II hypersensitivity rxns?
- Opsonization l/t phagocytosis or complement activation
- Complement-med lysis
- Ab-dependent cell-med cytotoxic (ADCC) usually d/t NK cells
Ab & complement lead to ___ ____ ___.
Membrane attack complex
What are the tests for Type II hypersensitivity rxns?
Direct & indirect Coombs’
What are Type III hypersensitiviy rxns?
Immune complex
What happens in Type III hypersensitivity rxns?
Ag-Ab (IgG) complexes activate complement, which attracts neutrophils
What do neutrophils release in Type II hypersensitivity rxns?
Lysosomal enzymes
What is Serum sickness?
An immune complex dz in which Ab’s to the foreign proteins are produced (takes 5 days). Immune complexes form & are depositied in membranes where they fix complement
Most serum sickness is now cause by drugs acting as ____.
Haptens
What are the sx of Serum sickness?
- Fever
- Uticaria
- Athralgia
- Proteinuria
- Lymphadenopathy
When does serum sickness present?
5-10 days after Ag exposure
Is serum sickness or Arthus rxn MC?
Serum sickness
What is Arthus reaction?
A local subacute Ab-med hypersensitivity rxn. Intradermal injection of Ag induces Abs which form Ag-Ab complexes in skin
What are the characteristics of Arthus rxn?
- Edema
- Necrosis
- Activation of complement
What causes Arthus rxn?
Ag-Ab complexes
What is the test for Arthus rxn?
Immunofluorescent staining
What is Type IV hypersensitivity rxn?
Delayed (T-cell med) type
What happens in Type IV hypersensitivity rxn?
Sensitized T lymphocytes encounter Ag & then release lymphokines (l/t macrophage activation; no Ab involved)
What are the 4 T’s of Type IV hypersensitivty rxn?
- T lymphocytes
- Transplant rejections
- TB skin test
- Touching (contact dermatitis)
What are the tests for Type IV hypersensitivity rxn?
Patch test & PPD
What are some examples of Type I hypersensitivity rxn?
- Anaphylaxis
- Allergic & atopic disorders
What is the presentation of Type I hypersensitivity rxns?
Immediate, anaphylatic, atopic
What are some examples of Type II hypersensitivity rxns?
- Autoimmune hemolytic anemia (AIHA)
- Pernicious anemia
- idiopathic thrombocytopenic purpura
- Erythroblastosis fetalis
- Rheumatic fever
- Goodpasture’s synd
- Bullous pemphigoid
- Pemphigous vulgaris
What is the presentation of Type II hypersensitivity rxn?
Dz tends to be specific to tissue or site where Ag is found
What are some examples of Type III hypersensitivty rxns?
- SLE
- Polyarteritis nodosa
- Poststreptococcal glomerulonephritis
- Serum sickness
- Arthus rxn
How do Type III hypersensitivity rxns present?
Can be assoc w/ vasculitis & systemic manifestations
What are some examples of Type IV hypersensitivity rxns?
- MS
- Guillain-Barré synd
- PPD
- Contact dermatitis
How do Type IV hypersensitivity rxns present?
Response is delayed & does NOT involve Abs
What is the pathogenesis of a Blood transfusions Allergic rxn?
Type I hypersensitivity rxn against plasma proteins in transfused blood
What is the clinical presentation of a blood transfusion allergic rxn?
- Urticaria
- Pruritus
- Wheezing
- Fever
What is the tx for blood transfusion allergic rxn?
Antihistamines
What is the pathogenesis of blood transfusion Anaphylactic rxn?
Severe rxn, IgA-def individuals must receive lood products that lack IgA
What is the clinical presentation of blood transfusion Anaphylactic rxn?
- Dyspnea
- Bronchospasm
- HOTN
- Resp arrest
- Shock
What is the pathogenesis of Febrile nonhemolytic transfusion rxn (FNHTR)?
Type II hypersensitivity rxn
Host Ab against donor HLA Ag & leukocytes
What is the clinical presentation of FNHTR?
- Fever
- HA
- Chills
- Flushing
What is the pathogenesis of an Acute hemolytic transfusion rxn (HTR)?
Type II hypersensitivity rxn
Intravascular or extravascular hemolysis
What is intravascular hemolysis?
ABO blood group incompatibility
What is extravascular hemolysis?
Host Ab rxn against foreign Ag on donor RBCs
What is the clinical presentation of a HTR?
- Fever
- HOTN
- Tachypnea
- Tachycardia
- Flank pain
- Hemoglobinemia
- Jaundice
What is hemoglobinemia an example of?
Intravascular hemolysis
What is Jaundice an example of?
Extravascular hemolysis
