Skin & Immune Mediated Diseases 3 Flashcards
what are hypersensitivtity reactions
an exaggerated or inappropriate immune response to a mild pathogen or innocuous substance (allergen)
what is an autoimmune disease
a specific humoral or cell-mediated immune response against the constituents of the body’s own tissues (auto-antigens)
what are the types of hypersensitivity reactions
type I: anaphylactic, immediate
type II: antibody-dependent, cytotoxic
type III: immune complex mediated
type IV: cell-mediated, delayed
the host reponse to an imagined insult or an over-reaction to a real (but sometimes unidentified or unknown) infectious agent (ex. aberrations of normal immune reactions)
what is type I hypersensitivity
production of antigen specific IgE –> IgE is bound to mast cell membranes
re-exposude to antigen
mast cell degranulation –> release of vasoactive mediators (histamines and prostaglandins) –> severe systemic reaction anaphylaxis or a milder local reaction
what is anaphylaxis/anaphylactic shock
immediate systemic reaction caused by rapid IgE-mediated
what does anaphylaxis/anaphylactic shock cause
immune release of potent mediators from tissue mast cells and peripheral basophils
serious allergic reaction that is rapid in onset and may cause death
what does anaphylaxis/anaphylactic shock involve
involves skin +/- mucosal tissue; resp. system; gastrointestinal system; reduced BP
what is the process of anaphylaxis/anaphylactic shock
release of vasoactive mediators > systemic vasodilation & increased vascular permeability > hypotension & tissue hypoperfusion
what arre the triggers of anaphylaxis
foods
medication
venoms
unidentified
(not all reactions involve IgE –> some triggers directly stimulate mast cells)
what are examples of type I hypersensitivity
- apopic dermatitis
- insect bite hypersensitivity (flea bite)
- drug eruptions
- food allergy
what accounts for majority of skin disease in dogs and cats
atopic dermatitis
flea bite hypersensitivity
what causes atopic dermatitis
multifactorial (genetics + environment)
what is a common cause of atopic dermatitis
environmental allergens –> commonly house dust mites, insects, pollen, mold, dander of other animals
what is the predisposition of atopic dermatitis
seems to be inherited
10% of dogs affected
esp WHWTs, cairns, scotties, boxers
what does atopic dermatitis cause and where are common locations
pruritic dermatitis and otitis (conjuctivitis)
face, feet, ventrum
itching, red skin, loss of fur, small pus filled or solid bumps in skin, sores that might ooze, recurrent skin and ear infections
what does atopic dermatitis appear histologically
acute inflammation with mast cell rich infiltrate
®how do allergies cause atopic dermatitis
allergens can be absorbed via the skin +/- inhaled
what contributes to the pathogenesis of canine atopic dermatitis
abnormal skin barrier
- variation in filaggrin expression
- disorganized lipid lamellae
- altered balance of antimicrobial peptides
what research is being done to prevent atopic dermatitis from abnormal skin barrier
repair lipid barrier in dogs by topical applications or nutritional supplements
what is insect bite hypersensitivity
allergic dermatitis –> acute or more often chronic
what triggers cause insect bite hypersensitivity
- fleas
- biting midges
- black flies
- mosquitoes
how does insect bite appear on histology
focal necrosis beneath surface crust
reaction often characterized by eosinophils
what is flea bite hypersensitivity
type 1 hypersensitivity (and/or type IV)
common - no breed predilection
may be seasonal –> summer & autumn
what does flea bite hypersensitivity
pruritic papular dermatitis (miliary eczema)
dorsal lumbosacral area, neck, inner thighs, abdomen
what is the features of flea bite hypersensitivity histology
may include eosinophils in dermal infiltrate and/or intraepidermal eosinophilic abscesses
what is this
flea bite hypersensitivity
eosinophil exocytosis, pustules & scale-crust
what is this
crusted papules & alopecia
what is type IV hypersensitivity delayed type hypersensitivity
DTH reactions involve same processes as cell-mediated immunity to microbial infection –> not dependent on antibody
balance swings from protection to tissue damage if the stimulus is great or unusually persistent
what occurs in type IV hypersensitivity
sensitized T-cell population develops after initial contact with antigen via ACPs –> re-exposure –> lymphocyte activation –> cytokine release –> macrophage infiltration
tissue damage is due to activated macrophages and cytotoxic T cells
what are delayed hypersensitivity reactions
what is the tuberculin test
an example of DHT
- antigen introduced into subcutaneous tissue and processed by local antigen-presenting cells
- A TH1 effector cell recognized antigen and release cytokines which act on vascular endothelium
- recruitment of T cells, phagocytes, fluid and protein to site of antigen injection causes visible lesion
how does DTH reaction cause a granuloma
granuloma formation depends on prolonged stimulation (> 2 weeks)
what is a disease that causes granulomas
tuberculosis
what is allergic contact dermatitis
type IV hypersensitivity
chemical (hapten) binds to epidermal proteins to form allergen
not commonly diagnosed in animals –> difficult to distinguish from irritant contact
what is the appearance of allergic contact dermatitis
variably pruritic maculopapular dermatitis –> sparsely haired regions affected especially ventrum –> feet, legs, perineum, scrotum, chin and pinnae
what is the histological appearance of allergic contact dermatitis
chronic dermatitis with hyperplasia, hypergranulosis, compact hyperkeratosis and lymphocyte exocytosis
what is type III hypersensitivity
direct damage mediated by antibodies to exposed cell surface antigens –> antigen usually endogenous
binding of antibody (IgG or IgM) +/- complement –> cytolysis or cytotoxicity
what causes type II hypersensitivity
underlies various autoimmune disorders affecting various tissues –> pemphigus, pemphigoid (epidermal cells), hemolytic anemia (red blood cells)
what type of hypersensitivity is sweet itch
?
what triggers sweet itch
culicoides spp. hypersensitivity
what are the key features of flea bite hypersensitivity
type I hypersensitivity
seasonal –> summer and autumn
pruritic papular dermatitis (miliary excema)
dorsal lumbosacral area, neck, inner thighs, abdomen
histoloy: eosinophils in dermal infiltrate and/or intraepidermal eosinophilic abscesses
what type of hypersensitivity is delayed type
type IV hypersensitivity
name 2 autoimmune conditions which have a hypersensitivity component
type II hypersensitivity
pemphigus, pemphigoid (epidermal cells), hemolytic anemia (RBCs)
what is shown here
allergic contact dermatitis
give an example of delayed type hypersensitivity relevant to vet med
tuberculosis
what is the difference between hypersensitivity reactions and autoimmune disease
hypersensitivity: exaggerated or inappropriate immune response to a mild pathogen or innocuous substance (allergen)
autoimmune: a specific humoral or cell-mediated immune response against the constituents of the body’s own tissues (auto-antigens)
