HSR Flashcards
(23 cards)
What are hypersensitivity reactions?
Exaggerated or inappropriate immune responses to an antigen or allergen produced by the normal immune system
Includes allergies and autoimmunity
How many types of hypersensitivity reactions are there?
Four types
Type I, Type II, Type III, Type IV
What is Type I hypersensitivity reaction?
IgE mediated immediate reaction
Involves B lymphocytes, plasma cells, mast cells, basophils, neutrophils, and eosinophils
What is the time frame for Type I hypersensitivity reactions?
Less than 30 minutes to appear
Considered immediate hypersensitivity
What happens during the first contact with an antigen in Type I hypersensitivity?
Sensitization occurs with activation of B lymphocytes and formation of IgE-secreting plasma cells
IgE binds to mast cells and basophils
What are the effects of mediators released in Type I hypersensitivity?
Increased vascular permeability, smooth muscle contraction, vasodilation, eosinophilia, neutrophilia, increased gastric secretion, increased nasal and lacrimal secretions
Mediators include histamine, LTB4, LTD4, prostaglandins, and PAF
What is an example of systemic anaphylaxis?
Administration of anti-tetanus serum (ATS)
Clinical features include itching, erythema, and shock
What is Type II hypersensitivity reaction?
Antibody-mediated reaction involving humoral antibodies that attack cell surface antigens
Main antibodies are IgG and IgM
What is the typical onset time for Type II hypersensitivity reactions?
15-30 minutes after exposure to antigen
May appear after a longer duration
What are the main participants in Type II hypersensitivity reactions?
Complement system, tissue macrophages, platelets, NK cells, neutrophils, eosinophils
Tissue-specific reactions
What is the mechanism of injury in Type II hypersensitivity?
Antigen-antibody complex formation leads to cell lysis via the complement system
Involves opsonization and phagocytosis
Name an example of Type II hypersensitivity reaction.
Autoimmune hemolytic anemia
Other examples include transfusion reactions and Graves’ disease
What characterizes Type III hypersensitivity reactions?
Immune complex-mediated reaction resulting from deposition of Ag-Ab complexes on tissues
Leads to inflammation and cell injury
What is the onset time for Type III hypersensitivity reactions?
About 6 hours after exposure to the antigen
Not tissue specific
What can precipitate Type III hypersensitivity reactions?
- Persistence of low-grade microbial infection
- Extrinsic environmental antigens
- Autoimmune process
Antigen-antibody complexes fail to be removed
Give an example of Type III hypersensitivity reaction.
Systemic lupus erythematosus (SLE)
Other examples include immune complex glomerulonephritis and rheumatoid arthritis
What is Type IV hypersensitivity reaction?
Cell-mediated delayed hypersensitivity reaction without antibody formation
Involves sensitized T lymphocytes
What is the typical onset time for Type IV hypersensitivity reactions?
About 24 hours after exposure to antigen
Effects can last up to 14 days
What is the role of CD8+ T cells in Type IV hypersensitivity?
Recognizes the antigen and activates macrophages
Involves antigen presenting cells (APCs) and helper T cells
Name an example of Type IV hypersensitivity reaction.
Mycobacterial infection (tuberculosis)
Other examples include contact dermatitis and drug hypersensitivity reactions
What is the primary treatment for immediate hypersensitivity reactions?
Management of anaphylaxis with I.M adrenaline (epinephrine)
Other treatments include IV antihistamines and oxygen
What are common treatments for allergic bronchial asthma?
- Inhaled short-acting bronchodilators
- Inhaled corticosteroids
- Leukotriene antagonists
Disodium cromoglycate may also be used
What is the treatment for Type IV hypersensitivity reactions?
Treatment of the eliciting cause
Includes antibiotics for tuberculosis and leprosy
