HYPERSENSITIVITIES:TYPE I HYPERSENSITIVITY Flashcards
Immune mediated hypersensitivity is
An inflammatory response to an antigen that is inappropriate (unwanted)
Antigen is not part of a pathogen.
For example, allergies to pollen
Inflammation is excessive and damages the host more than the pathogens.
Allergies to bee stings
Allergen is
Often called allergies.
An inciting antigen is called an allergen.
Allergies and sites
May be limited to a specific site.
May involve the whole body.
If this is severe → anaphylactic shock
Anaphylactic shock is
Generalized poor tissue perfusion as the result of allergic vasodilation.
Define an alergen
an adverse reaction to a substance or material
Define an allergen
antigen, the thing causing the allergic reaction
Type 1 hypersensitivity is provoked by
IgE
Type 2 hypersensitivity is caused by
IgG or IgM binding to normal tissue
Type 3 hypersensitivity is caused by
Antibody-antigen complexes activate immune response.
Type 4 is caused by
T cells and Macrophages directly cause inflammation.
Type 1 is also called
IgE mediated hypersensitivity
Immediate hypersensitivity
What is the most common cause of allergy
Exaggerated type I responses are the most common cause of allergy.
Why is type 1 called IgE mediated
Because IgE is pre-bound to mast cells
Rapid response to allergen (minutes)
Why does type 1 hyper happen
Some animals genetically produce more IgE
Some dogs
Some antigens naturally produce very strong IgE responses.
Wasp and bee stings
How does mast cells work in type 1 hyper
Some IgE responses are appropriate.
Mast cells are sentinel cells and use bound IgE as a method to detect invaders.
Internal parasites (worms)
Mast cells can release chitinase. (kayh-tin-aze)
Destroys parasite outer covering.
Attract eosinophils which also help to destroy the worm
Steps after an allergen binds to IgE in type 1 hyper
The mast cell degranulators
Release IL-31
Stimulates pruritus
Release histamine and heparin
Vasodilation and increased capillary permeability
Attract eosinophils
IgE bounds to
Remember that most IgE is bound to mast cells (some on basophils, eosinophils)
Signs of type 1 hyper
Redness, swelling (edema) and itchiness.
Three types of allergic dermatitis
Three types: atopy, food allergy, parasite allergy
Atopy defintiion
The genetic disposition to allergic disease
An increased production of IgE
Become sensitized to common environmental antigens
Terriers, Dalmations, and Retrievers are particularly susceptible.
Mixed breed dogs are less susceptible
Causes of atopic dermatitis
Contact with environmental allergen
Skin keratin defect?
Seen in some people with allergic skin disease.
Microbial colonization
Immune dysregulation
Causes of food allergies
Ingested
From gut
A small amount of dietary protein is absorbed intact.
May/may not be GI signs (increased defecation, vomiting, diarrhea)
Absorbed allergen binds to skin mast cells
Signs of allergic dermatitis
Often seen in younger adults
Characterized by pruritus
Itching can be intense
Often the first sign
Skin lesions caused by allergic dermatitis look like
Hives /urticaria
Raised lumps, small or large
Warm, edematous, pruritic
Erythema
“Hot Spots”
Signs of atopic skin disesae
Skin lesions
Face, feet, axillas, ventral abdomen and groin are common areas affected
Scratching/licking/rubbing leads to secondary damage to skin
Erythema
Hair loss
Thickening
Pigmentation
Secondary infections
Food allergies that cause allergic dermatitis c/s
Recurrent ear infections
Recurrent anal gland problems
Pruritus – feet, ears,eyes, axilla, perianal region
Exclusion diet is and used for
Food Allergy
Time consuming – pruritus should improve within 4 weeks; full trail is 8-12 weeks in duration
Skin testing is and used for
Atopic Dermatitis
Inject potential allergens into skin (ID) and see if there is a reaction.
Largely limited to veterinary dermatologists
Serum testing is and used for
Atopic Dermatitis
Better at ruling out allergens.
Prevention and treatment of allergic dermatitis
Washing and bathing
Reduce inflammation
Remove source
Desensitization
Changing to less inflammatory diet
Dietary exclusion
How to bath a dog with allergic dermatitis
Especially useful for contact dermatitis
tepid/cool water
Emollient (moisturizing) shampoos
Oatmeal is anti-pruritic
Lots of shampoos and topical products available
What medications are used for allergic dermatitis
Antihistamines – not particularly effective
Corticosteroids – immunosuppressant (high dose) and anti-inflammatory
Atopica (cyclosporin) – immunosuppressant
Oclacitinib (Apoquel)
Janus kinase (JAK) inhibitor
Inhibits IL-31 and other cytokines
Monoclonal antibody against IL-31 (cytopoint)
Reduces pruritus
Removing allergen source in allergic dermatitis
Look for and remove environmental allergens
Kill fleas and prevent reinfestation.
House/stable horses to avoid culicoides midges
House dust allergies?
Can be very challenging with certain environmental allergens
Desensitization fo allergic dermatitis
Allergen specific immunotherapy- injectable vs sublingual
Aim is to switch from synthesis of IgE to IgG
Gradually increasing doses of allergens
Changing diet for allergic dermatitis
Changing to a less inflammatory diet – Atopic Dermatitis
Increase omega-3 fatty acids
Fish
Supports skin barrier
Dietary exclusion for allergens
Basis of treatment for food allergies
Feed a simple diet
Feed novel proteins
Lamb, duck, venison
Can add back protein sources to identify problem
Anaphylaxis caused by parasites
Rupture of warble pupae in cattle
Rupture of hydatid (tapeworm) cysts
Allergic dermatitis caused by parasites
Flea saliva (flea bite hypersensitivity)
Culicoides (midge) bites in horses
Sweet itch – urticaria and intense pruritus
Mosquitos
Hay fever and asthma is and caused by
Hay fever (allergic rhinitis) and asthma are both IgE mediated hypersensitivities - the difference depends on where the antigen gets trapped.
Large particles get trapped in the upper airways and cause hay fever
Small particles are carried down into the lungs and cause asthma
Mainly a people problem
Signs of hay fever and asthma
Nose: Sneezing, watery nasal discharge, blocked nasal passages, itchy nose
Eyes: Itchy, red, swollen, may feel gritty, in people blueness below skin
Throat: Soreness, itchy
Sleep – mouth breathing and fatigue
Asthma is most common in signs and treatment
Cats, basenjis, people and horses
Signs:
Wheezing and dyspnea
Can be acute and severe.
Diagnose by giving bronchodilator
Hay fever and asthma in techs
Less likely if you have a lot of siblings and were raised on a farm.
More likely if there is a family history.
Can be seasonal.
Often an allergy to pollens from any type of plant or spores from fungi
Can occur year round
Often an allergy to dust mites, roaches, animal dander, fungi, and molds
Dander allergies are more of a concern if you work indoors.
Fine dander (cats and rabbits) is more likely to cause asthma and/or hay fever.
In cats, the main allergen is a salivary protein that gets stuck to hair during grooming
A feline diet containing antibodies against cat allergens reduces allergic burden and helps people with allergies.
Purina Pro Plan LiveClear
Anaphylactic shock occurs due to
Generalized mast cell degranualtion
Anaphylactic is a concern when
Giving any biological product
e.g. Vaccines, Penicillin
How long does anaphylactics take to develop
Typically 15-30 minutes
What to have on hand for anaphylaxis
Should always have epinephrine, antihistamines, and corticosteroids on hand
Fatal if not recognized and treated promptly.
Which organ predominates depends on the species in anaphylaxis
Lungs and the GI tract are the major shock organs
Which organ predominates depends on the species
Lungs and GI – horses, cats
Lungs only – cattle, sheep
Liver – dogs
Why are the kidneys and skeletal muscles NOT affected by anaphylaxis?
Few sentinel cells
Resp signs of anaphylaxis
Increased RR
Dyspnea
Cough
GI signs of anaphylaxis
Vomiting (not in horses or rabbits)
Increased defecation/diarrhea (may be bloody)
Signs not involving resp or GI in anaphylaxis
Cats - irritation and scratching around the head.
Urination
Weakness (lethargic)
Lack of coordination (ataxia)
Collapse
Death
Antihistamines are given by and used for
Diphenhydramine (Benadryl)
2-4 mg/kg IM, PO, SQ every 8-12 hours
Injectable to treat an allergic reaction or anaphylaxis
Oral if given prophylactically or after initial injection.
Epinephrine works by
Stabilizes mast cells
Reverses vasodilation
Dilates smooth muscle (helps breathing)
Rapidly absorb if given IM or SQ
Dose for cats and dogs is 0.1 to 0.5 mL of 1:1000 epinephrine.
Which Corticosteroids are used for anaphylaxis
Prednisolone sodium succinate (Solu-Delta-Cortef)
Dexamethasone in water
-Not the propylene glycol preparation
-Not absorbed properly if in the propylene glycol
