[Adult pulmonary Langerhans' cell histiocytosis].

INTRODUCTION Adult pulmonary Langerhans'cell histiocytosis, also referred to as histiocytosis X, is a disorder of unknown etiology which affects preferentially young smokers. The disease is characterized by granulomatous lesions which progressively invade and destroy distal airways, leading to the formation of characteristic cicatricial kystic lesions. Florid granulomas contain numerous Langerhans'cells, antigen-presenting cells of the dendritic cell lineage, associated with T lymphocytes and eosinophils. The diagnosis rests on the combination of clinical and radiologic data, and particularly on high-resolution CT scan findings showing a typical association of nodular and cystic changes, predominantly in the upper and middle lobes. Further evaluation with surgical lung biopsy is indicated in less typical situations. CURRENT KNOWLEDGE AND KEY POINTS The pathogenesis of Langerhans'cell histiocytosis is not fully understood, but several arguments suggest that the disease results from an abnormal immune reaction initiated by Langerhans'cells and directed against the bronchial epithelium. Other arguments suggest the presence of genetic abnormalities susceptible, for example, to increase the sensitivity of these cells to cytokines (GM-CSF, or others) known to influence their survival and maturation. FUTURE PROSPECTS AND PROJECTS These recent advances in the pathogenesis of Langerhans'cell histiocytosis could promote the development of new therapeutic strategies designed to regulate the number and activated state of Langerhans'cells in specific lesions.