ON ALLERGY

An allergy is a miscarriage of the immunology process in which something that begins as a protective device has deleterious consequences that range in severity from itching to sudden death.

Sir Peter Medawar -Nobel Laureate

Millions of people all over the world are troubled by a variety of annoying and painful ailments caused by a physiological phenomenon known as ‘allergy’. Some typical allergic disorders are hay fever, sensitivity to certain plants, dust, pollen and domestic animals and reaction to certain foods and drugs. Allergic reactions can also prove fatal as in severe cases of asthma or anaphylactic shock caused by an insect’s sting, or by a drug such as penicillin.

Certain aspects of allergy are of interest to doctors. They noticed that injections of mould, dust or pollen extracts help 80 per cent of allergy victims build some resistance to those substances though the cause was not known. (Such injections are rarely given for allergies to foods or animals.) Antihistamines bring relief from certain symptoms, though their effectiveness is not uniform. In recent years there has been a remarkable spurt of activity in the study of allergic conditions.

A major breakthrough was achieved in the previous century at Denver by two Japanese doctors. Scientists had known that allergens (substances causing allergy), stimulated certain cells known as mast cells in the skin and in the mucous membranes of the respiratory and gastro-intestinal tracts to release histamine and other chemicals, that assist the body in fighting an infection following an injury, but prove to be irritants in an allergic reaction.

When an allergen enters the skin, histamine dilates the capillaries turning the area red and causes inflammation. Histamine can also make breathing difficult by stimulating secretion of a mucous and constricting the involuntary muscles involved. But doctors did not know how allergens could make the mast cells release chemicals.

Though it had been believed that a certain type of antibody or immunoglobulin (a complex molecule that protects the body against foreign substances) was involved, scientists had neither identified this antibody nor understood how it worked. Doctors using them­selves as guinea pigs decided to concentrate their research on this aspect, experimenting with extracts of ragweed pollen and tiny amounts of an allergy victim’s serum (the fluid part of the blood).

They succeeded in isolating the elusive immunoglobulin E (IgE), one of the five classes of antibodies produced by the immune system. Most antibodies travel about freely in the body eliminating trespassers. This is what happens when allergens enter the bodies of non-allergic people. However, IgE behaves differently About 5, 00,000 IgE molecules which are ‘Y’ shaped are embedded tail first in the membranes of the mast cells.

When an allergen particle comes along it unites with the upper portion of two neighbouring IgE molecules bridging the gap. The pull involved in the process makes the cell release histamine and other chemicals; the severity of the reaction depends on the amounts of allergen and IgE, and hov. prone the mast cell is to discharge.

Most common allergies can be traced in this fashion to the presence of IgE. It may appear rather strange that the body should produce such a troublesome agent as IgE, but it is now known that IgE can play a useful role also, providing defence against invaders that attack layers of tissue exposed to the environment, such as the skin and the respiratory tract.

Some theorists have postulated that allergy may reflect partly a hyperactivity of the immune system and is also probably a hereditary trait. During the last 5,000 years people with an ability to resist infectious diseases would have survived epidemics and passed on the trait to their offspring.

Hereditary

This may explain the wide prevalence of allergy today. Any allergy treatment that completely eliminates IgE production might seriously weaken a patient’s internal immunity. But lowering of the IgE level in an intelligent manner might prove useful.

Further researches carried out in the United States have enabled identification of substances that enhance or suppress the immune system’s production of IgE and they are now trying to find out what controls the formation of those substances. Two types of white blood cells, T. cells and B. cells seem to be involved. B. cells produce IgE whereas T. cells make the substances that can turn this production on or off.

The conditions under which the T. cells produce either a substance that stimulates the formation of B. cells that bring forth IgE or a substance that turns off the IgE producing B. cells have been studied. Steps are being taken to analyse the structure of the ‘suppressor’ and the ‘enhancer’ both of which are proteins having similar molecules and seem to compete for gaining access to the same control site on the IgE producing B. cell, the winner being the one having more number of molecules.

Some scientists were hopeful of finding a drug that can regulate the production of a patient’s own IgE sup­pressor—perhaps one drug for all allergies involving IgE. In fact they are hopeful of using suppressors from human cells for therapy. But other scientists do not share such optimism.

New Theory

American scientists have also come out with a new theory called ‘allergic breakthrough’.They believe that IgE levels are regulated by a ‘damping mechanism’ that represents the balance of the suppressor and enhancer. The IgE level should normally be low. When the damping mechanism is disturbed by a huge blitz of allergen, the IgE production increases thus resulting in an allergic breakthrough and a full blown attack.

Any changes in this system may cause allergies to appear and disappear. This would explain why every exposure to or contact with pollen or dander does not necessarily result in an attack. The allergen may not be adequate to cause production of enough IgE. No wonder many routine diagnostic tests indicating a positive result for certain allergens can prove misleading. The patients concerned may never react to those substances in the real world. Small doses of allergen increased gradually to a maintenance level may work on the damping mechanism and depress IgE levels. The allergen injected would be enough to produce non-IgE antibodies which would out number the IgE molecules and swoop down on the offenders and eliminate them before they can begin IgE production. The success of a new type of injection containing polymerised allergens appears to support such a theory

Yet another scientist was interested in studying what happens to a mast cell when the allergen collides with it. A series of biochemical reactions take place leading to the cell releasing its contents. Since enzymes are responsible for such processes, an enzyme inhibitor should be able to prevent the series of reactions and reduce allergy symptoms without interfering with other cell functions.

Mast Cell

Some scientists were planning to identify the two dozen chemicals inside the mast cell and also to identify others that form when IgE and allergen get attached to the mast cell and to inhibit the cell from spilling out the chemicals in response to an allergen. A drug called cromolyn sodium appears capable of preventing mast cells from spilling their contents. But it may not be desirable to block the release of chemicals completely, since these chemicals also have some useful functions.

When it was noticed that antihistamine drugs which had been developed in the middle of the previous century had failed to relieve many allergic conditions such as asthma, doctors began to took for other mast cell chemicals. A couple of decades later they successfully identified a group known as leukotrienes, hundred times as potent as histamine in producing inflammation and swelling and in contracting involuntary muscles.

They are unusual sulphur-bearing compounds that play a major role in asthma and anaphylactic shock. Scientists at Harvard, United States, are concentrating on developing antileukotrienes which may well become the most promising weapons against allergic disorders in the coming decades.

A few hints at preventing or controlling allergy:

          1.       Avoid dust. Prevent dust from accumulating in living rooms.

          2.       Avoid pets such as cats.

          3.       Avoid pollen

          4.       Do not take medicines (particularly injections, containing such medicines) which have ingredients to which you are known to have allergy

          5.       Try antihistamines recommended by a physician. They bring quick relief in several conditions.

          6.       Use a steroid nasal spray or an inhaler.

          7.       If you are feeling very miserable try an allergy shot, after con­sulting your doctor.

If you are crossing forty, you could feel optimistic that the allergen may simply go away by itself due to the immune system itself becoming lethargic.