[Actualities in extrinsic allergic alveolities or hypersensitivity pneumonitis]

Significant advances have been noticed in the pathogenesis and the diagnosis of extrinsic allergic alveolitis during the last few years. Indeed the immune mechanism and the enabling conditions have been more precisely defined, the clinical stages and the diagnosis criterias clearly defined, new antigens incriminated and some etiological agents have been reclassified. The present pathogenic explanation insists on the type IV hypersensitivity reaction with sensitization of T lymphocytes, activation macrophages, the formation of IgG type antibodies and immune complexes, activation of complement and secretion of cytokines. The involvement of certain HLA classes (HLA2, DR3, DRB1, DQB1), interaction of genetics and environments factors, the role of infections agents and smoking have been demonstrated in several studies. The development of news clinical and biological diagnosis criteria have led the discovery of new extrinsic allergic alveolitis in the work places, a better knowledge of the prognostic elements and an appropriate adaptation of prevention measures.