Introduction: Allergy Special Issue

Allergy involves abnormal variations of normally protective immune responses that, in predisposed (atopic) subjects, trigger immediate hypersensitivity to normally harmless antigens. Many elements of the immune system are involved and a number of symptoms of varying seriousness can be triggered by a wide range of allergens from many sources and with different features. Although allergic responses are abnormal, they are very common and affect a considerable, and increasing, proportion of the population; for example, worldwide up to 50% of school children are sensitized to one or more common allergen. There is, thus, a clear drive for understanding the complex mechanisms involved in allergy and to find ways to combat it.