MECHANISMS OF ALLERGY
Allergy mechanisms are far-reaching and complex, including overload, toxicity, true allergy, intolerance etc. Use this platform to explore different types of allergic mechanisms. You need to read most or all of these to gain a proper understanding of what this section is all about. Remember: more than one mechanism may be operating in your case!
IN ANY EVENT, READ THIS INTRODUCTION FIRST, BEFORE YOU JUMP OFF.
Unfortunately, we run into a problem right away, which is that there is no real consensus agreement on exactly what constitutes an allergic reaction. The water is made muddy by classic allergists, scared of infringements on their lucrative territory, claiming that only they deal with “real” allergies. Their representatives bodies, such as the American College of Allergy and Immunology, continue to produce position papers, which effectively dismiss any one else’s view as fraud. But in their eager fury to try to destroy the competition, they leave vast armies of patients high and dry. To merely negate anything other than the classical allergy model is to fail to address the many different and similar mechanisms by which external triggers can cause disease in unlucky individuals but not in the population at large.
I have always worked with the very simple “shorthand” definition of allergy which in layman’s terms is: something you should avoid because you will feel better if you do!” This empirical (hands-on) approach is based on the following clinical criteria:
This is eminently sensible and is how the term is used today in popular usage. The layman does not need to know the mechanisms of allergy, hypersensitivity and intolerance but can readily grasp the concept of ‘something to avoid’.
The historic view
Let us take an overview and see if this leads to more understanding, starting with the historical perspective. The word allergy was first coined by an Austrian paediatrician, Clemens von Pirquet, in 1906. He defined an allergy as an acquired, specific, altered capacity to react to a physical substance on the part of the tissues of the body. This description is worth considering in more detail :
Acquired means that it is not in-born or constitutional, though there is no doubt that the tendency to allergies runs in families. In what is now the ‘classic’ allergic reaction, an individual must meet the substance (at least once) and the allergy results from this initial sensitizing encounter.
Babies that appear to be born with an allergy do not really conflict with this theory. It’s just that they made their first contact while in the womb (with, for example, a food in the mother’s diet).
Specific means that it is not a generalized reaction but relates to one exact substance or, in reality, often a small part of a molecule of that substance. An individual may react to many things at once but each reaction is unique. Even if several allergens (allergy-causing substances) provoke the same effect, it is simply that the final end-organ stimulated is the same in each case.
Altered means the reaction is not ‘normal’. In other words, not everyone shares the same experience. The majority of our species would probably not react in the way an allergic patient does. For example, most of us eat tomatoes safely, yet some people cannot do so without risking a severe asthma attack or some other unpleasant con-sequence.
However, there are difficulties in this last interpretation. Once you start to move outside the immunological guidelines for an allergy, phenomena such as an allergy to wheat become very common. Probably half the population or more don’t tolerate it anything like as well as they suppose, once you start asking the right questions. We may retain the adjective ‘altered’ perhaps, but such reactions may be anything but rare or unusual.
Furthermore, when it comes to a matter such as low-grade poisoning (see below), then substances that induce symptoms are toxic for everyone. ‘Allergy’ then becomes only a matter of degree. Sensitive people react to levels of the toxin that would be tolerated by the average individual.
In the 1920s the sort of reaction von Pirquet was talking about was commonly found to have an immunological basis, ie. it was an antigen-antibody phenomenon. Apparently, the body was responding to foreign protein (and even food is considered ‘foreign’ by the body since it is ‘non-self’) by mounting an antibody attack. The spin-off from this interaction, rather like fall-out from a chemical battle, was what gave rise to the unwanted and inappropriate symptoms experienced by the patient.
something radically wrong, however, with this simplistic and narrow definition,
though immunologists cling to it like a raft at sea. The great paradox – as
pointed out by Professor John Soothill (personal
communication) - is
that if this explanation were true, we all ought to get allergic reactions to
food every time we eat. Obviously this doesn’t happen. Somehow the body knows not
to react against food protein.
Unfortunately for those who stand by this rhetoric, even as early as 1920 Dr Albert Rowe and others were able to demonstrate that there were clear reactions to ingested substances and that these could be established to exist beyond any doubt, regardless of the lack of adequate explanation. Since these reactions also accord with von Pirquet’s original definition, there seemed nothing wrong with calling them allergy – in this case, food allergy.
There was no real controversy at the time, since Rowe was not an internationally known figure. He continued his seminal researches, wrote his book Food Allergy: Its Manifestations, Diagnosis and Treatment (Lea and Febiger, Philadelphia, 1931) and departed the world stage. However, his successors, notably Randolph, Rinkel and Zeller, authors of Food Allergy (Charles C. Thomas, Springfield, Illinois, 1951), carried on Rowe’s work and, particularly since the 1950s, the proof that dietary allergies could exist without there being any demonstrable antibodies became steadily more and more compelling – to the embarrassment of immunologists. If these immunologists admitted the existence of food allergy at all, they’d say it was ‘very rare’ and applied only to a very tiny minority of the population. Randolph, Rinkel and Zeller were finding far too many cases.
As the debate hotted up in the 1970s and 1980s the two groups polarized and antagonism grew more unpleasant. To ease the situation, the term ‘food intolerance’ was introduced in a booklet published jointly in 1984 by the Royal College of Physicians and the British Nutrition Foundation. This was an attempt to try and accommodate the fact that unpleasant reactions to food clearly did exist, but nonetheless the die-hard immunologists wouldn’t give in and allow the term ‘allergy’ to be applied. In many ways this was a poor compromise, especially since proponents of the term cannot provide any explanation of how ‘intolerance’ comes about.
THERE FOLLOWS THE KEY SECTIONS OF ALLERGIC MECHANISMS AND A BRIEF EXPLANATION:
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