[Allergens]

The clinical signs linked with immediate hypersensitivity, correspond with an abnormal reactivity of the immune system, which appears following contact with external substances, the allergens. Over the last few years there has been considerable progress in research on these substances in the domain of structural characterisation, biochemistry and immunological properties. Besides the definition of the word allergen linked to its immunological characteristics, our usual language maintains a certain ambiguity in its use which may characterise different states, including successive steps of the manufacture of an allergen extract. In effect the word allergen may designate the agent that is responsible for the allergic disease, for example cat, but also the raw material used for the manufacture of the corresponding extract, whether it be hair or squames; it may also apply to the final allergenic extract, the extract of cat hair or squames, as well as a precise molecule such as the major allergen of cat Fel d1 in the same example. After having reviewed several definitions as well as the nomenclature we will study the general characteristics of pneumoallergens and trophallergens, those of recombinant allergens, then the parameters of manufacture of allergen extracts.