Type I and II Hypersensitivity Flashcards
What are hypersensitivity reactions?
A hypersensitivity reaction occurs when a patient has an undesirable and clinically detectable immune reaction after antigen exposure
Dysfunctional response to an antigen causing harm tot he patient
What is a type I hypersensitivity reaction?
IgE production with an inflammatory response of predominantly eosinophils and lymphocytes causing disease
Occurs in seconds to <1 hour
What are allergens?
Antigens that have special properties to prime a Th2 response
Proteases are the most common allergen
Stable, bind to MHC II on APC
What is the first step to developing a type I reaction?
First exposure to allergen activates Th2 cells to produce IL-4 and start class switching to IgE
Takes a minimum of 5-7 days
What does IgE bind to on a mast cell?
Fc(epsilon)RI receptors on mast cells
IgE is only operational when bound to its receptor on a mast cell, basophil, or eosinophil
What initiates mast cell activation?
Cross linking of IgE to the surface of allergen
What mast cell products are premade and pre-stored in the cell prior to activation?
Proteases (e.g. chymase)
Histamine
Heparin
What is a part of the early phase reaction in type I hypersensitivity?
Vasoactive components and proteases are released from mast cells
Causes vascular dilation, smooth muscle contraction (increased permeability) and tissue damage
What is the late phase reaction of type I hypersensitivity?
Eosinophilic inflammation
May cause tissue remodeling damage in chronic diseases like asthma
4 hours-2 days
What is the treatment for anaphylaxis?
Epinephrine given intramuscularly
Stops mast cell activation, must be given immediately
How do you test for Type I hypersensitivity?
ELISA for specific IgEs to allergens - in vitro
Introduction of small quantity of allergen percutaneous or intradermal skin testing
What are treatments for type I hypersensitivity diseases (nonchronic)?
Anti-histamines for immediate phase
Epinephrine for anaphylaxis
What are treatments for chronic type I hypersensitivity diseases?
Topical glucocorticoids - interrupt late phase
Anti-leukotriene antagonists for late phase
Anti-IgE, IL-4, or IL-5 monoclonal antibody
What is a hapten?
Small peptide which is too small to be presented to a T cell
E.g. Penicillin
However if it binds to albumin it becomes large enough for T cell recognition and IgE production
What is a type II hypersensitivity reaction?
Specific antibody binds antigen on cell surface and causes gain or loss of function by effecting a receptor’s activity or killing the cell by complement mediated lysis or opsonization
> 2 to 24 hours to occur
