Delayed hypersensitivity Flashcards
What is Type II hypersensitivity?
A hypersensitivity reaction mediated by IgG or IgM antibodies that target antigens on cell surfaces or extracellular matrix
What mechanisms cause tissue damage in Type II hypersensitivity?
Complement activation opsonization antibody-dependent cellular cytotoxicity (ADCC) and inflammation
What are common examples of Type II hypersensitivity reactions?
Hemolytic anemia Goodpasture syndrome and rheumatic fever
What happens in hemolytic anemia caused by Type II hypersensitivity?
Antibodies target red blood cell surface antigens leading to their destruction by complement or phagocytosis
What is the mechanism of Goodpasture syndrome?
Antibodies bind to basement membrane antigens in the lungs and kidneys causing inflammation and tissue damage
What is antibody-dependent cellular cytotoxicity (ADCC) in Type II hypersensitivity?
Antibodies bind to cells recruiting NK cells to kill the target cell via perforin and granzymes
How does rheumatic fever involve Type II hypersensitivity?
Antibodies against streptococcal antigens cross-react with heart tissue causing inflammation and damage
What treatments are used for Type II hypersensitivity?
Corticosteroids plasmapheresis to remove antibodies and immunosuppressive drugs
What is Type III hypersensitivity?
A hypersensitivity reaction caused by immune complexes formed between antigens and antibodies that deposit in tissues
What are immune complexes?
Aggregates of antigens and antibodies that can activate complement and recruit inflammatory cells
What happens when immune complexes deposit in tissues?
They trigger inflammation complement activation and tissue damage
What are common examples of Type III hypersensitivity reactions?
Systemic lupus erythematosus (SLE) post-streptococcal glomerulonephritis and serum sickness
What is the mechanism of SLE in Type III hypersensitivity?
Autoantibodies form immune complexes with nuclear antigens which deposit in tissues and cause inflammation
What happens in post-streptococcal glomerulonephritis?
Immune complexes formed after a streptococcal infection deposit in the kidney glomeruli causing inflammation
What is serum sickness?
A reaction to foreign proteins in antiserum causing immune complex deposition and systemic symptoms like fever and rash
What is the Arthus reaction?
A localized Type III hypersensitivity reaction caused by immune complex deposition at the site of antigen injection
How does complement contribute to Type III hypersensitivity?
Complement activation by immune complexes leads to inflammation vascular permeability and recruitment of neutrophils
What is the role of neutrophils in Type III hypersensitivity?
Neutrophils are attracted by immune complexes and release enzymes and reactive oxygen species causing tissue damage
What treatments are used for Type III hypersensitivity?
Corticosteroids immunosuppressive drugs and plasmapheresis to remove circulating immune complexes
What is Type IV hypersensitivity?
A cell-mediated hypersensitivity reaction involving T cells and cytokines occurring 24 to 72 hours after antigen exposure
What cells mediate Type IV hypersensitivity?
TH1 cells CD8+ T cells and macrophages
What are common examples of Type IV hypersensitivity reactions?
Contact dermatitis tuberculin skin tests and graft-versus-host disease
What cytokines are involved in Type IV hypersensitivity?
IFN-gamma TNF-alpha and IL-12
What is the mechanism of Type IV hypersensitivity?
Antigen-presenting cells activate TH1 cells which release cytokines to recruit and activate macrophages and CD8+ T cells
What happens during the sensitization phase of Type IV hypersensitivity?
T cells are primed by antigen-presenting cells and develop antigen specificity
What happens during the elicitation phase of Type IV hypersensitivity?
Antigen re-exposure activates memory T cells leading to cytokine release and tissue damage
What are common causes of contact dermatitis in Type IV hypersensitivity?
Allergens like nickel poison ivy and latex
How does the tuberculin skin test involve Type IV hypersensitivity?
It measures immune memory to Mycobacterium tuberculosis antigens by inducing a delayed inflammatory response
What is graft-versus-host disease (GVHD) in Type IV hypersensitivity?
Donor T cells attack recipient tissues after transplantation causing a delayed inflammatory response
What treatments are used for Type IV hypersensitivity reactions?
Corticosteroids immunosuppressive drugs and antihistamines to control inflammation
How does Type IV hypersensitivity differ from Types I II and III?
Type IV is mediated by T cells and does not involve antibodies whereas Types I II and III involve antibody-mediated mechanisms
