Exam 2- Type I Hypersensitivity Flashcards
what is an inflammatory response that causes extensive damage to the host’s tissues, even death, called?
hypersensitivity or allergy
IgE-mediated type I hypersensitivity (immediate hypersensitivity) is caused by coming into contact with an antigen against which the host has ________________________
pre-existing IgE antibodies
where are high affinity Fc-epsilon-RI receptors found?
mast cells, basophils, and eosinophils
true/false: allergens are typically presented to the immune system as high doses
false: very low doses
which Th cell response is required to induce type I hypersensitivity reactions?
Th2
what do mast cell granules do?
potent mediators immediate hypersensitivity reactions
how are mast cells, basophils, and eosinophils activated once the IgE molecule is bound?
cross-linking of the Fc-epsilon-RI receptors
what are the primary and secondary mediators?
primary: pre-formed and stored in granules, immediate hypersensitivity
secondary: synthesized after or released by enzymatic breakdown of cell membrane phospholipids during degranulation process
is histamine short-lived or long-lived?
short-lived
is the genetic predisposition to develop Type I hypersensitivity multigenic?
yes
true/false: the majority of IgE in the body is present in blood
false
true/false: mast cells of non-allergic individuals have IgE antibodies bound to the surface of their mast cells
true
what are the phases of type I hypersensitivity?
sensitization phase
activation phase
effector phase
what does the “wheal and flare reaction” show?
locally dilated blood vessels engorged with red blood cells
what does the late phase reaction of type I hypersensitivity consist of?
accumulation of inflammatory leukocytes
what inhibits the late phase of type I hypersensitivity reactions (rich in eosinophils)?
corticosteroids, not antihistamines
what is allergic rhinitis?
airborne antigens react with IgE-sensitized mast cells in nasal passages and conjunctiva
what is system anaphylaxis or anaphylactic shock caused by?
systemic release vasoactive mediators (mainly histamine and leukotrienes)
what are the two antibody based tests for diagnosis of allergies?
radioallergosorbent test (RAST)
ELISA
what classes of drugs are given for therapy for allergies?
antihistamines
antileukotrienes
corticosteroids
epinephrine
cytopoint
how does allergen immunotherapy work?
shift towards allergen-specific IgG production
shift to Treg subset which suppressed Th2 response
what is the principle protective function of IgE-mediated immune reactions?
readication of parasitic worms such as helminths
what do eosinophils release in response to their Fc-epsilon-RI receptors binding to IgE and cross-linking?
major basic protein (MBP)
true/false: allergy shots lead to induced Treg response against the allergen used in the shots
true
where is most of the IgE in the body?
bound to Fc receptor Fc-epsilon-RI on mast cells, basophils, and eosinophils
what is the sequence of events for immediate hypersensitivity?
antigen exposure
activation Th2 cells for the antigen
cytokine help from Th2 cells to B cells
class switching to IgE
production IgE
IgE binds to Fc receptors on mast cells
re-exposure of antigen
what does it mean that allergens are multivalent?
have one or more epitopes that are repetitive, and IgE response mounted against those epitopes
what cytokines do Th2 cells produce?
IL-4, IL-5, IL-13
what does the cytokine IL-4 do?
helps allergen-specific B cells class-switch to IgE
what does the cytokine IL-5 do?
activates eosinophils- common in many immediate hypersensitivity reactions
what does the cytokine IL-13 do?
stimulates epithelial cells to secrete increased amounts of mucus
what cytokine is significantly higher in severely allergic individuals?
IL-4
how are mast cells and basophils activated by IgE?
cross-linking of the Fc-epsilon-RI receptors
what is the difference between primary and secondary mediators in hypersensitivity reactions?
primary: pre-made and released immediately: immediate hypersensitivity
secondary: synthesized or released by enzymatic breakdown of cell membrane phospholipids during degranulation process
are histamine’s actions short-lived or long-lived?
short-lived because it is rapidly catabolized
what are the actions of histamine?
leakage plasma into tissues
vasodilation
increased peristalsis and bronchospasms
what are the actions of prostaglandins?
vasodilation
bronchoconstriction
is histamine stronger acting than leukotrienes?
no, leukotrienes are much stronger and longer lasting
more potent bronchoconstrictors and stimulators of vascular permeability and mucus secretion
what are important cytokines that mast cells produce in hypersensitivity?
TNF-alpha: inflammation
IL-4: Th2 response
what causes the late phase reaction after the wheal and flare reaction (2-6 hours)?
accumulation inflammatory leukocytes: neutrophils, eosinophils, basophils, and CD4+ Th2 cells
true/false: the late phase reaction is rich in eosinophils
true
chronic inflammation in asthma is associated with increased presence of ___________, ___________, ___________, and _____________
lymphocytes
eosinophils
neutrophils
other leukocytes
what is the difference in food allergies and food intolerances in presenting signs?
food allergies: itching and skin problems
food intolerances: diarrhea or vomiting
what is in the cutaneous inflammatory infiltrate in dermatitis?
mast cells
dendritic cells
low numbers eosinophils and neutrophils
what are the main vasoactive mediators released in systemic anaphylaxis?
histamine and leukotrienes
what are the two antibody based tests for diagnosis of type I hypersensitivity?
radioallergosorbent test
ELISA
