Langerhans Cells in Squamous Cell Carcinoma

To the Editor.—  Alcalay et al¹ report a reduction in numbers of Langerhans cells (LC) and alterations in their morphology, with loss of dendrites in some squamous cell carcinomas. They speculate that tumor proliferation may destroy the dendrites or that the LC surrounded by the malignant keratinocytes may lack a stimulus that is required to maintain dendritic morphology. Other workers have noted that following application of potent sensitizers such as dinitrofluorobenzene to mice,² or urushiol³ or dinitrofluorobenzene⁴ to guinea pigs, LC numbers were reduced and adenosine triphosphatase staining patterns were altered with loss of dendritic processes. We have observed apparently similar changes in LC density and morphology following appplication of the sensitizer dinitrochlorobenzene to human skin. We have previously shown that the degree of allergic sensitivity induced by a range of doses of dinitrochlorobenzene follows predictable log dose-response relationships.⁵ We were therefore interested to see