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
What is Mysthenia Gravis?
Antibody directed against the acetylcholine receptor at the neuromuscular junction
What is idiopathic thrombocytopenic purpura?
Anti-platelet antibody initiates opsonization by splenic macrophages
Bleeding or bruising (purpura) from low platelet count
What is the acute management for ITP?
Glucocorticoids - global immunosuppression
IVIG - removal of functioning antibody
What is the chronic management for ITP?
IVIG - removal of functioning antibody
Anti-CD20 monoclonal - rituximab
What are in vitro methods of testing for type II hypersensitivity reactions?
Identifying specific antibody production
What are ex vivo tests for type II hypersensitivity in Good Pasture’s disease?
Renal biopsy
What is hemolytic disease of the newborn?
Rh- mother has Rh+ fetus
During first pregnancy delivery, mother makes Rh antibody
During second pregnancy antibodies cross the placenta and lyse the fetus’s RBCs
Baby dies shortly after birth
How do you test for hemolytic disease of the newborn?
Direct Antiglobulin Test - Coombs
Measures antibodies already bound to the RBC of the baby
Indirect - test mother’s serum for anti-RBC antibodies
What drugs can cause a type II hypersensitivity reaction?
Penicillin
Cephalosporins
Hydrochlorothiazide
Methlydopa
