16 - Hypersensitivity (Nicole) Flashcards
(49 cards)
Hypersensitivity reactions are balances between
Self and non-self
4 types of hypersensitivity reactions
Type 1, type 2, type 3, type 4
A hypersensitivity reaction is a
Exaggerated immune response that causes host damage exceeding damage caused by inciting antigen or pathogen, and requires pre-sensitization of host
Hypersensitivity reactions cause reproducible
Clinical signs initiated by exposure to an antigen at a dose that is tolerated in normal animals
Most important physiological feature of Type 1 reactions
Antigen interacts with IgE bound to mast cells (or basophils)
Does immediate hypersensitivity continue for long periods?
It does have a late phase influenced by cytokine activity characterized by infiltration of eosinophils, macrophages, neutrophils, and T cells, but will be gone after 1 day
What happens in allergies with cross-linking
At second encounter with antigen, mast cell receptors cross-link to antigen, creating strong activation that starts degranulation. If you don’t have an allergy, NO cross-linking
Name 3 clinical characteristics of allergy
Increased vasodilation - histamine & PGF-2a
Increased vascular permeability - histamine, PGF2a,leukotrienes
Smooth muscle spasm-histamine, pGF2a, leukotriones
Cellular infiltration - cytokines, leukotrienes, granule associated chemotactic factors
Do the clinical signs of allergy change depending on where the antigen gets in?
Yes - ingestion might lead to vomiting, diarrhea, anaphylaxis whereas inhalation leads to allergic rhinitis or bronchspasm
Cutaneous anaphylaxis clinical signs
Pruritus (redness), hyperemia, angioedema
Cardiovascular anaphlyaxis clinical signs
Hypotension
Anaphylaxis respiratory clinical signs
Bronchospasm, laryngeal edema, dyspnoea
What theory has been advanced to explain increases in allergy incidence?
Hygiene hypothesis - proposes that exposure to some pathogens early in life provides a better T-cell balance
What explains why countries with improved hygiene are experiencing increases in asthma and allergy rates
Hygiene hypothesis
Type 2 hypersensitivity reactions have IgG or IgM directed against
Self antigens
3 basic antibody mediated mechanisms
- Opsonization and increased phagocytosis
- Complement mediated and Fc-receptor mediated cell cytotoxicity
- Antibody-mediated dysfunction
Sequestered antigen
Cannot interact with immune system during development as they are anatomically sequestered - lymphocytes specific for sequester antigens are not deleted (eye, CNS, joints)
Disease associated with type 3 hypersensitivity q
Myasthenia gravis
IMHA
Immune-mediated hemolytic anemia - results during type 2 hypersensitivity
Serum sickness is associated with which type of hypersensitivity
3
Is it problematic when antibodies are in excess, antigens are in excess, or when there’s equivalence (type 3 hypersensitivity)
Equivalence - forms complexes that are not soluble
Type 3 hypersensitivity: immune complex formation and deposition in tissue eliciting
Acute inflammatory response
Formation and deposition of immune complexes depends on
High antigenic load, size complexes, and mononuclear phagocyte’s ability to remove efficiently
Immune complexes deposit locally or systemically: examples
Vasculitis - in vessels
arthritis - in joints
glomerulonephritis - in renal glomeruli
