The first distinction that recurs in the allergy literature is between immediate and delayed patterns of allergic reactivity which 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 that can be diagnosed by allergy skin tests and by IgE antibody tests. Hay fever is a reaction to airborne plant pollens in the nose. Allergy tests are positive, antihistamines help and allergy shots can sometimes reduce the reactivity over time.

Bias toward Simple Ideas American and Canadian allergists tend to focus on type 1 hypersensitivity mediated by IgE-armed basophils and mast cells. Some of these physicians view allergy practice as exclusively concerned with type 1 reactions and ignore or diminish any effort to describe, investigate and understand other forms of immune reactivity.

Thus two camps have arisen:

1. An exclusively IgE group and 2. An IgE plus other mechanisms group.

The type 1 model is easier to study and easier to deal with in practice, so the exclusively IgE-group tends to dominate the literature and demands compliance with the IgE-model. The IgE model is simple and linear: the same responses are expected from a sensitized individual with repeated challenges; skin tests, serum IgE measurement, and double-blind oral challenges are correlated

Even when applied to patients with clearly defined IgE-mediated allergy, the model is unrealistic since no human body is a linear machine. While single, discrete allergic responses do occur, they are not the only reactions and are not fully characteristic of immune networks. Patients tend to have evolving and multiple reaction patterns over time, and show marked variability in their reactivity with repeated antigen challenges.

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