WHAT IS ALLERGY?

by Dr. M. P. Vora

The Home Doctor
A practical guide to good health

Vol. II, No. 7 of November 1963

Page No. 1 to 4

Allergy is an explanation of certain human ills such as asthma, eczema, urticaria or nettle-rash, hay fever, serum shock, serum disease, angioneurotic edema, involvement of skin, brain and intestine etc., which are grouped as diseases of allergy.

The word allergy was coined by Von Pirquet in 1906 to indicate altered reactivity or certain changes of reaction induced by the first injection of serum (not related to immunity). It denotes the sensitization reaction of a man and includes or is very nearly synonymous with hypersensitiveness, sensitization, idiosyncrasy, anaphylaxix and atopy. It conveys exaggerated susceptibility to various foreign substances or physical agents that are harmless to the great majority of persons. These substances may be endogenous (from inside the body) or exogenous (outside the body). Hippocrates was the first to lay the foundation of allergy by observing the physical excentricity of occasional persons to certain foods. Then followed the instances of unusual responses of some persons to commonly prescribed drugs. Such effects were called idiosyncracies.

Our present day knowledge of allergy, though still vague and far from complete, is an accidental by-product of the generalized use of antesera (diphtheria and tetanus). Occasionally any one of these sera produces either a prompt violent reaction (serum shock) that at times, ends in fatality, or a generalized urticaria in about 10 to 14 days (serum disease) or an artificial sensitiveness (anaphylaxix). In the case of a person who has developed an artificial sensitiveness as the result of first injection of serum, second injection of the same serum after a sufficient interval of time (10 to 14 days), is followed by an explosive reaction or anaphylactic shock.

An array of seemingly unrelated and dissimilar conditions such as asthma, eczema, urticaria, hay fever and human manifestations of allergy which may be: -

• A manifestation of familial or hereditary trait.
• The unusual and abnormal reaction of body cells to the presence of the substance which under normal conditions produces no obvious reaction in a normal person.

Allergic state is the potential specific reactivity due to the existence of antibody (in body cells) which links the cells to the specific substance, antigen. Allergy is the resulting reaction, altered from the normal of the species, when union of antigen with antibody is affected. It must be understood that allergy is not a single or uniform biologic phenomenon. There are different pathogenic, etiologic, pathologic and immunologic as well as clinical varieties. Allergic reactions are fundamentally chemical or physio-chemical reactions rather than biologic. It is possible to create allergy with a few substances. Instances of development of altered reactivity are seen daily. For example, the gardener who has handled a certain flower for years without any trouble, begins to suffer, without an apparent cause, from an eczema each time he comes in contact with flower; a nurse has to discontinue the use of certain antiseptic lotion or soap for the same reason; and the person who finds that he can no longer eat fish or strawberries without suffering from urticaria. Such altered reactions are specific for the substance. Skin allergy is intimately bound up with immunity as can be seen from the results of small-pox vaccination.

• Allergy may be normal, physiologic or induced:
• Injection of a small dose of horse-serum such as diphtheria or tetanus ante serum produces serum sickness in about 10% of all cases. In his serum, antibodies are developed and the man has become sensitized and remains so for some time there-after. Serum disease is but an incident in the development of sensitization. He becomes anaphylactic and is likely to die of shock if the serum is again injected at the proper time (after 10 to 14 days). Artificially sensitized man loses his sensitivity within a time of few weeks.
• Dermatitis often results from contact with a great variety of substances such as certain dyes, anti-septic lotions, vegetable oils. But neither the new-born nor an adult develops dermatitis with the first application of these substances. Second application 2 to 4 weeks after the first, gives an intense eruption. Obviously the skin eruption is not due to any toxic or irritating quality of the substances but due to sensitization developed as a result of earlier contact.
• Not infrequently infection with a particular bacterium or a fungus may produce a state of reactivity to that organism or its products. The focal infection need not be active to produce its remote effects. The relationship between the primary infection and its subsidiary expansion through the skin is readily recognized in acute infection but not so in chronic infection.

The above three are typical examples of clinically different reactions which are explained by allergy, since the primary action of antigen is neither toxic nor irritatative. One sensitization results from contact with serum, another from the contact with dye lotion or oil, and the third from bacterial or fungus infection. They are superficially induced at will by a contact.

• Allergy may be spontaneous, hereditary or pathologic:

Asthma, hay-fever and angio-neurotic edema show striking contrast to induced allergies. They cannot be artificially produced by contact, they seem to appear spontaneously and paternal as well as maternal heredity seem to be an important predisposing factor. This type of allergy shows the extreme degree of reactivity, variety of sensations and its long continuation. Contrast may or may not be necessary to set off the allergic mechanism in man; or a very mild contact is enough to initiate a variable highly reactive and self-perpetuating allergy to one or more substances predetermined by nature or heredity. We do not know how the sensitization starts, what determines the allergen or clinical form of the allergy for the particular case, why one becomes reactive to pollen, another to food while third to infection- all is not clear to understand.

The exciting causes of an allergic reaction in man that is allergens- are many and varied. They may absorbed by ingestion, inhalation, injection from a focus of infection or from external contact. Allergic reactions show several different types of reactions, exhibiting varying ‘functional’ lesions (such as edema, hyperemia, and running of the nose) or ‘organic’ lesions (such as weeping eczema, hyper plastic sinusitis, productive rhinitis, haemorrhages).

A person who has developed asthma or eczema and reacts on skin test with serum , is a person who is very likely to react violently and immediately, often fatally, if injected with serum. That is why doctors would like to know history and antecedents of a patient and have to resort to skin test before ante serum can be injected. These procedures often help in the diagnosis of allergy. The man who is artificially sensitized and the man who has been spontaneously sensitized both are reactive to skin test, giving the immediate urticarial wheal; and sera of both transfer this reactivity to normal human skin.

In spontaneous or hereditary allergy, the skin test may show immediate or delayed reaction. Delayed type of reaction occurs after the same incubation period. Though its mechanism is not known, its existence is clear. It is common to get delayed type of reaction in cases of urticaria, angio-neurotic edema and eczema. Positive skin tests do not always signify clinical sensitiveness. Similarly negative skin tests do not always mean absence of immediate clinical reaction.

Some authorities differentiate between allergy and anaphylaxix. Anaphylaxix requires a preliminary sensitizing injection. It has a definite incubation period usually ten days, anaphylactic sensitivity is specific, anaphylactic state can last for weeks, years or throughout life, anaphylactic reaction is of brief duration but often intense and frequently fatal following the injection of serum. It is more common and constant. It is predictable. It can be transferred passively.

Allergy is a phenomenon of far reaching importance, but one which is difficult to define, vaguely sensed rather than clearly demonstrated, and in which illustrations convey its significance more clearly than definitions. Allergy has familial tendency, nervous element, diathesis, it is not so common and constant, it does not need such obvious preliminary sensitization, allergic reactions persist for days or weeks, passive transference is not common and is limited in nature.