Allergy and Autoimmunity Flashcards
Allergy
- an inappropriate immune response to a harmless foreign antigen
- systemic allergic reaction-severe
- localised allergic reaction:
- skin
- respiratory tract
- gastrointestinal tract
Most common hypersensitivities we see in regards to allergic disease
Type I and Type IV
- type I is by far the most common
- sometimes get type III (VERY RARE)
- and sometimes type IV
COP and Canine Lymphoma
- Lymphoma is the most common haematopoietic malignancy in dogs, and is the most responsive to chemotherapy
- The most common physical finding in dogs with lymphoma is peripheral lymphadenopathy (disease of the lymphnodes) which is usually generalized but may be localized to a single lymph node or a region of the body
- Much of the information regarding efficacy of treatment for canine lymphoma has come from studies using combinations of cyclophosphamide, vincristine, and high dose prednisone. COP is a relatively non-toxic protocol and is relatively inexpensive.
- Overall, COP chemotherapy causes complete remission in about 70% of dogs with lymphoma for a median of 130 days.
- We need to be careful with these drugs though as they can cause GIT effects (V&D), Bone marrow suppression, Immunosupression, Vincristine -induced tissue necrosis if given extravascularly
Different Inflammatory Cell Types
Anaphylaxis
- serious, life-threatening allergic reaction
- The most commonanaphylactic reactions are to foods, insect stings, medications.
- If you are allergic to a substance, your immune system overreacts to this allergen by releasing chemicals that cause allergy symptoms
- Always a type I hypersensitivity Reaction!!
Systemic allergic reactions- Manifestations
- Acute type I hypersensitivity- can be triggered by drugs, plants, food, insect bite / sting
- Urticaria- mild reaction Dermal wheals ± pruritus
- Angioedema- Reaction progresses to subcutaneous tissues swelling of eyelids / lips
- Anaphylaxis / anaphylactic shock- Systemic mast cell degranulation & histamine release hypotension-dangerous & severe reaction, often preceded by V&D (in dogs as they have more mast cells in gut) or dyspnoea (in cats as they have more mast cells in respiratory tract)
Therapy for Systemic Hypersensitivity
- Epinephrine to treat the hypotension caused by anaphylactic shock
- Antihistamines (e.g. PiritonTM)
- Steroids e.g. dexamethasone, prednisolone (at anti-inflammatory dose)
- Salbutamol- inhaler for humans bronchodilation, less easy to administer to animals, often given by IV
Allergic Skin Disease
MOST COMMONLY TYPE I HYPERSENSITIVITY
- Flea allergic dermatitis- get sensitised to proteins in flea saliva (dogs scratch, cats over-groom)
- Atopic dermatitis Allergic reaction to environmental allergens (pollens, house dust mite etc.)- initially seasonal but can–> non-seasonal as they become sensitised to more allergens
-Dogs (westies= ↑ susceptible) can be very itchy–> secondary trauma & often opportunistic infection
• Feline eosinophilic granuloma complex
• Sweet itch in horses- Allergic reaction to midge (culicoides) bites, often affecting dorsum & base of tail
*Type IV hypersensitivity: Allergic contact dermatitis
Allergy Testing
- Intradermal skin testing- shave dog, dot with pen & inject with a different allergen at each dot, wait & check for reaction
- Serology (AllerceptTM)- send serum off to look for IgE antibodies, uses an enzyme labelled Fcε receptor
Treatment of Allergic Skin DIsease
- Flea control
- Hypoallergenic diet trial
- Topical shampoos
- Desensitisation- tries to reinstate tolerance by injecting the allergens at increasing doses
- Medication: Evening primrose oil, Antihistamines (don’t work well in dogs), Prednisolone, Cyclosporine (immunosuppressive drug used as last resort), Antibiotics for secondary infection
Allergic Respiratory Disease
- Feline asthma- mast cells (in lungs in cats) around airways get sensitised & react pro-inflammatory mediators vasoconstriction & mucus secretion
- Allergic bronchitis in dogs
- Inflammatory Airway Disease (IAD) (aka heaves/ COPD) in horses- usually caused by allergic response to mould spores in crappy hay–> Coughing, wheezing, exercise intolerance
Immune Mediated GIT Disease
- Gluten sensitive enteropathy- seen in Irish setters, similar to coeliac disease- hypersensitivity to gluten in diet–> chronic diarrhoea & weight loss
- Inflammatory bowel disease- Inappropriate immune reactivity to dietary or enteric microbial antigens
IBD
(allergies)
Underlying causes of IBD
-Inappropriate immune reactivity to dietary or enteric microbial antigens, usually a combination of factors:
- ↑intestinal permeability- more antigen gets across, less likely to stimulate Tregs
- Inappropriate IgE response to harmless antigen–> ‘parasite response’ in absence of infection
- IgA deficiency (GSDs)
- Poor T regulatory cell responses
- Defective innate immune response to bacteria (PRRs not working properly)
Treatment of IBD
- ↓ antigenic stimulation: Hypoallergenic diet (FRD) or Antibiotics to reduce microbial load (ARD)
- Reduce inflammation in the GIT: Steroid therapy. If really bad, use other immunosuppressive drugs (cyclosporine)
Autoimmunity
Breakdown of tolerance to self-antigen (this occurs all the time but is usually mild & transient)
• Failure to regulate pathological immune responses is the main issue
Susceptibility to Autoimmune Disease
- Genetic factors - Predominantly MHC genes- cocker spaniels= predisposed to IMHA due to MHC type - Other immune response genes include TNF alpha & CTLA4
- Hormonal factors - e.g. SLE predominantly in females
- Environmental factors - Infection, stress, diet (Vit D) etc
