Mechanisms involved in the production of an allergic response:
Definition: Type 1 hypersensitivity response results from the IgE response to an antigen. In the body antigen contact activates IgE production in B-cell series lymphocytes found in the blood. The IgE then binds to mast cell Fc-receptors sensitising the mast cell. Mast cells are found in the tissues. Repeated antigen contact with cell bound IgE leads to cross-linking of receptors and finally to a tight connection of IgE molecules. This tight connection initiates a biochemical cascade causing degranulation of the sensitised mast cell and release of inflammatory mediators. Clinical symptoms of a type-1 hypersensitivity reaction are seen. The particular symptoms depend on the tissue involved.
The antigen responsible for such a reaction is called an allergen.
Methods in allergy diagnosis:
Serological tests require the taking and submitting of a blood sample for testing.
Intradermal skin tests require the injection of the allergen into the skin and the measurement of the subsequent response.
of a suitable diagnostic method for allergen detection is important for
any successful therapy. Test systems vary regarding specificity and sensitivity(accuracy),
test principle, number and preparation of allergens and considerable differences
can be found between intradermal and serological tests in general and
between the various serological tests themselves.
Even further improvement has been achieved with the introduction of the Fce-receptor test. The Fce receptors are used to detect the allergen-specific IgE and this avoids cross reactions with the other immunoglobulins which would reduce the sensitivity and specificity (accuracy) of the test.
antibody test determines group antigens first. This inexpensive and reliable
test will then allow the choice of the appropriate single allergen testing.
Some examples of the single allergens tested:
If the result of an allergy test suggests there may be some benefit from hyposensitisation (immunotherapy) solutions can be prepared which are given to the animal in increasing concentrations and increasing intervals by injection. This hopefully causes the suppression of the IgE response. However careful consideration must be given to the selection of patients for this treatment - young animals, early start of treatment and lack of complicating factors, for example.
Food intolerance/allergy is a far more complex field and can involve many different types of reaction. It is therefore not wise to use IgE testing to exclude the presence of a food allergy. The usual suggestion here is to feed an exclusion diet and to reintroduce one food at a time, if this is felt to be necessary. Many pet food manufacturers have included various diets in their ranges to make this relatively straight forward. - If the animal is better why risk causing a relapse?
For more information, please contact:
Mrs Jackie Casey BVetMed MRCVS