[Immunological bases and classification of allergy].

The task of the immune system consists of destroying foreign structures in order to prevent the invasion of living organisms by pathogens. This destruction often provokes adverse effects defined as hypersensitivity reactions. The classification of hypersensitivity reactions proposed by Gell and Coombs is based on effector mechanisms. Although this framework remains largely used, recent work demonstrated the occurrence of profound similarities between different classes of hypersensitivity reactions. Indeed, all these reactions involve the activation of adhesion mechanisms intended to allow the local recruitment of blood leukocytes and cytokine production. The concept of a separation between two different modes of immune response induced by two different T lymphocyte subpopulations (TH1 and TH2) proved useful in understanding hypersensitivity reactions, although it represents only an approximation. Recent results were an incentive to develop new diagnostic and therapeutic strategies whose usefulness will be evaluated in the near future.