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Food digestion and assimilation represent the largest challenge facing the immune system. Assuming complete digestion, an intact intestine, a sturdy constitution, and minimal antigenic exposure such that the immune system is not overwhelmed, all goes well. A problem in one or more of these areas can result in immune attacks upon foods as if they were foreign invaders. Many disease conditions including arthritis, dermatitis, otitis, rhinitis, recurrent sinusitis, and inflammatory bowel disease have been associated with food reactions. Many food related diseases are difficult to diagnose because reactions can be either immediate or delayed. When the relationship between food and symptoms is hard to pin down by using elimination, measuring antibody levels to various foods and co-relating the findings with the patient's history and symptoms provides a means to recognize and manage food allergies.
The definition of "allergy" is much debated. Immunologists describe four types of hypersensitivity reactions. These are named Type I, Type II, Type III, and Type IV. Type I reactions are mediated by IgE antibodies and are characterized by the release of histamine. These are the immediate-onset allergies such as hay fever. Type II reactions involve antibody-mediated destruction of tissue following adherence of foreign material. Penicillin reactions are an example of a Type II reaction. Type III reactions are mediated by mixed immunoglobulins, but primarily IgG. Complexes composed of antigen and antibody activate complement and cytokines resulting in an inflammatory response. Type III reactions constitute the basis for delayed onset food allergies. Type IV reactions are cell mediated where T cells are the primary players. When activated by antigen, they react and kill bacteria, viruses, tumor cells or other target cells.
Type I food allergies manifest as sinusitis, rhinitis, recurrent ear or eye infections, mouth breathing and post-nasal drip. The allergic reaction occurs immediately upon exposure to the antigen. The relationship between food and allergic reaction is easily recognizable. Type III food allergies present as dermatologic changes, joint pain, and asthma or recurrent infection. Any system may be affected and any symptom is possible depending on the individual's susceptibilities.
At the present time food antibody assessment in animals is done by measuring IgE. Elevated level of IgG antibodies parallel those of IgE. Depending on the patient's symptoms one can assess immune complex disease by measuring IgE antibodies and following the clinical response of the patient after dietary changes are instituted. Food antibody assessments are also valuable as a preventive measure for patients that are not currently experiencing overt symptoms of an allergic reaction. Elevated levels of antibodies can signify subclinical immune reactions which, if ignored, may place cumulative stress on the immune system and over time setting the stage for the development of illness.
It is well documented that food allergy is an expression of an inherited predisposition. This predisposition results in disease when digestion is inadequate, This may be due to hypochlorhydria, pancreatic enzyme deficiency, or inadequate brush border enzymes. When proteins are not digested to amino acids, or short chain polypeptides, they retain their antigenic properties. these antigenic molecules may then be absorbed through a damaged mucosal barrier or "leaky gut" and be exposed to the immune system. This, in turn, can create a state of chronic immune hypersensitivity and inflammation. In general, foods with a higher protein content (> 20 %) are more likely to be allergenic.
Most of the time, adopting a hypoallergenic diet will produce resolution of symptoms. But, if leaky gut is severe, measures must be taken to promote intestinal healing. The addition of pre and probiotics to the diet will usually produce dramatic improvement. There is some data to suggest that lactobacilli and other probiotics can be used as treatment of food allergy when avoidance is not possible. Conventional treatment of allergies involves attempting to desensitize the animal by weekly injections of specially prepared serums for 3 to 5 years- and possibly for life as the latest advisory by the Academy of Veterinary Dermatology recommends.
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