Monday, November 07, 2005

The Concept of Allergy

The concept of immune responses to food antigens is useful in understanding many diseases. Many of the major unsolved disease of our civilization are either degenerative and/or inflammatory and many are recognized to be inflammatory, immune-mediated, hypersensitivity diseases. In this review, a general theory of hypersensitivity disease as a continuum of disease-causing mechanisms is presented.

The term "hypersensitivity" refers to immune-mediated processes that lead to disease. For over 20 years, I have considered the possible role of food antigens in causing or contributing to immune-mediated diseases and looked for opportunities to help patients with simple and safe therapeutic strategies such as diet revision. The original concept of allergy included all immune-mediated disease and the term allergy was interchangeable with the term "hypersensitivity."

Allergy can be thought of as hypersensitivity disorders with external causes. Substances that trigger allergic responses are antigens. These are often proteins that can be found in air, food and water. Airborne antigens such as plant pollens or house dust are well known. Other airborne antigens and food antigens are less obvious. New and foreign substances introduced to the body such as drugs and herbs cause allergic reactions.

Food materials should be given priority consideration since this is the biggest chunk of the environment to get inside human bodies and to interact with immune networks. If the term "food allergy" refers to all interactions between molecules derived from the food supply and the immune system, then many hypersensitivity disorders fall into the category of food allergy. Diverse manifestations of food allergy can only be understood if different patterns of immune activity are appreciated. It is unreasonable to believe that all food allergy can be detected by skin tests or any other simple test.

The first distinction that recurs in the allergy literature is between immediate and delayed patterns of allergic reactivity that loosely correspond to IgE-mediated allergy and non-IgE mediated responses. Many authors refer to the original four categories of immune-mediated injury defined by Gell and Coombs. The concept of four mechanisms is just a starting point for understanding immune-mediated disease. These very complicated defense-injury sequences cause a variety of disease states.

The immediate or type 1 allergy pattern is easily recognized because it involves quick and dramatic symptoms. Hay fever is the most common type 1 allergy and can be diagnosed by allergy skin tests and by IgE antibody tests such as RAST or ELIZA. Delayed patterns of allergy are not so obvious and generally go unrecognized. Allergy skin tests do not show this problem. Symptom onset is delayed many hours after exposure to the trigger. Allergic reactions to drugs such as penicillin and to foods involve delayed hypersensitivity.

The advocates of a broad definition of food allergy run the risk of being evangelical. The conviction that food allergy is a ubiquitous cause of disease comes from knowing the benefits of careful diet revision in medical practice. Many books in the popular literature proclaim the benefits of diet revision and a ground swell of interest and concern has engaged an ever-enlarging group of patients.
Often, the patient who benefits from proper diet revision is distanced from a medical profession who is either not interested or denies the problem of food allergy. Some of the issues that arise are semantic and political, but other issues involve the very complex biology of food-body interactions that are not well understood. Other issues involve the changes in the food supply that have accelerated in the past few decades.

When you do not know about food allergy, you are surrounded by mysterious diseases. When you know about food allergy, several common illness patterns begin to make more sense. Linda Gamlin writing about food allergy in the New Scientist stated that:

"Evidence is growing that many debilitating and chronic symptoms of ill health come from an intolerance for certain foods… The medical establishment remains largely hostile to the notion, leaving the field open to the medical fringe… the main problem is the plethora of symptoms and the variations from one patient to another. Doctors working with food intolerance report more than 40 possible symptoms and conditions...the severity also varies. Some patients are said to have nothing more than the occasional migraine or bout of fatigue, while at the other end of the scale the sufferer is unable to work or lead any sort of normal life."

In response to allergy lobby groups in the USA, the US Congress passed a bill that requires notice on the labels of foodstuffs that contain eight of the most common food allergens. The Food Allergen Labeling and Consumer Protection Act, will require plain English labeling by the year 2006 of products containing wheat, milk, soy, peanuts, tree nuts, fish, shellfish, or eggs. These account for an estimated 90% of all food allergies. The bill also requires the Food and Drug Administration to develop a definition of the term "gluten-free" to help those with celiac disease and who require a gluten free diet for other reasons.

See Allergy and Immunology by Stephen Gislason MD