Hypersensitivity

Abstract

Since it was established that an initial contact of the organism with certain infectious- toxic or noxious agents may result in the production of antibodies which protect the individual by lysing, neutralizing, or eliminating the foreign substance, numerous observations have indicated that the immunologic reaction does not always benefit the organism, and the organism is often damaged as s result. This type of harmful reaction is called an allergic or hypersensitivity reaction. The organism, tissue, or cell capable of exhibiting a hypersensitivity reaction is said to be sensitized. The allergic reactions, being immunologic reactions, are extremely specific, with the sensitized organism reacting exclusively with the antigenic determinant used for immunization or a similar structure. Hypersensitivity reactions are separated into two different types according to the time that elapses between the contact of the sensitized organism with the antigen and the macroscopic observation of the allergic phenomenon. Thus, whereas the so-called immediate hypersensitivity reactions require only minutes or perhaps a few hours to appear, delayed hypersensitivity reactions develop only after many hours. Today, although this criterion of the reaction time remains valid for classification of hypersensitivity reactions, it is understood that more important differences separate the two types.