Langerhans' cell histiocytosis

Some years ago the writing group of the Histiocyte Society1 divided histiocytosis syndromes in children into three classes: class I is Langerhans' cell histiocytosis; class II includes the familial and virus-associated haemophagocytic syndromes, sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman), juvenile xanthogranuloma, and reticulohistiocytoma; class III consists of the malignant histiocytic diseases. The estimated incidence of Langerhans' cell histiocytosis is about two to five cases per million yearly. The condition is characterised by abnormal proliferation and dissemination of histiocytes, which are almost identical to the normal dendritic cells first noted by Langerhans. These cells are typically present in the epidermis, interdigitating cells of lymph nodes, thymus, mucosal epithelium of the gastrointestinal and respiratory systems, and the cervix. Langerhans' cell histiocytes retain much of the surface antigen profile of normal dendritic cells. They also maintain function as antigen-presenting cells-ie, cells that fix antigens for presentation to other cells of the immune system, mainly T lymphocytes in the form of MHCs, to cause proliferation and intensification of the effect of T lymphocytes.2-4