8 - Type I Hypersensitivity Flashcards
Define what immune mediated hypersensitivity
an inflam response to an antigen that is inappropriate (unwanted)
Ag is not part of a pathogen ex allergies to pollen
inflame is excessive and damages the host more than the pathogen ex allergies to bee stings
often called allergies, inciting Ag is allergen
Briefly describe allergies and site (location)
may be limited to a specific site or may involve the whole body
if its severe may = anaphylactic shock (generalized poor tissue perfusion as a result of allergic vasodilation
Define allergy, anaphalaxis and allergen
Anaphalaxis -generalized poor tissue perfusion as a result of allergic vasodilation
Allergy - An inflammatory response to an antigen that is
inappropriate (unwanted
Allergen - inciting antigen
What are the four types of hypersensitivity reactions and what do they do?
Type 1: activaged by IgE
Type 2: IgG or IgM bind to normal tissue
Type 3: Ig-Ag complexes activate immune response
Type 4: T cells and macrophages directly cause inflam
Describe type 1 hypersensitivity or immediate hypersensitivity
mediated by igE, exaggerated type I responses most common cause of allergy. AKA immediate hypersens. b/c IgE is pre-bound to mast cells which rapidly respond to allergens within mins
Happens bc some prod more igE and some Ag’s naturally prod strong IgE responses (wasp/bee stings)
What role does mast cells play in type 1 hypersensitivity
mast cells are sentinel cels and use bound ige as a method to detect invaders such as internal parasites to activate mast cells, mast cells can also release chitinase(destroys parasite outer covering) and attract eosinophils which also help to destroy the worm
Explain the mechanism of how an allergen binds to IgE on a mast cell
The mast cell begins to degranulate and releases IL-31 to stim pruritus, it then releases histamine + heparin, causes vasodilation and inc capill permeability and attracts eosinophils
Signs of this are redness, swelling and itchiness
What is atopy?
The genetic predisposition to allergic dz characterized by an inc prod of IgE
they become sensitized to common enviro antigens
Which nbreeds are more suspectible to atopy?
terriers, dalmations, retrievers
mixed breeds also suspectible
What might cause atopic dermatitis?
Contact w/ enviro allergen such as microbial colonization, immune dysregulation and skin keratin defect, as seen in some people w/ allergic skin dz
How might food allergies be caused?
by being ingested and from the gut a small amount of dietary protein is absorbed intact
There may or may not be GI signs (like inc defecation, V/D)
Any absorbed allergens will bind to skin mast cells
What are some of the signs of allergic
Often seen in yger adults and characterized by pruritus (in which itching can be intense and is often the first sign)
What are the signs of allergic dermatitits - atopic skin dz?
Skin lesions such as hives/urticaria (raised lumps, sm or lg, warm, edematous, pruritic), erythema and “hot spots”
Occurs on face, feet, axillas, ventral abdomen and groin
other signs are scratching, licking, rubbing leads to 2ndary damage to skin like erythema, hairloss, thickening, pigmentation, 2nd infections
What are some clinical signs of food allergies?
reccurent ear infections, reccurent anal gland problems, prurius on feet, eyes, ears, axilla and perianal region
How do we diagnose food allergies and atopic dermatitis?
Food - exlusion diet. It is time consuming as pruritus should improve within 4 wks, full trial is 8-12 weeks
Atopic - inject potential allergens into skill intradermally for reactions and perform serum testing (better for ruling out allergens)
