Human herpesvirus 6 is present in lesions of Langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) is a disease characterized by Langerhans cell infiltration of skin and bone, with its most severe form manifested by multifocal infiltration of many organs. The etiology is unknown, although viral infection has been proposed as a potential pathogenic factor. Human herpesvirus 6 (HHV-6), a recently described member of the human herpesvirus family, has been associated with atypical or malignant lymphocytic processes, and immune disorders. Based on these observations, we suspected that HHV-6 may play a role in the pathogenesis of LCH. Lesional tissue of 30 patients with LCH was retrospectively examined for the presence of HHV-6 by using the polymerase chain reaction. Tissue specimens from 63 patients with other benign and malignant histiocytic and lymphocytic diseases served as controls. In addition, all specimens were examined with control primers specific for herpes simplex virus (HSV). HHV-6 DNA was detected in lesions of 14 of 30 patients with LCH (47%). On clinical subgroup analysis, HHV-6 DNA was found in 10 of 16 patients with extraosseous disease (63%) and in four of 14 patients with disease limited to bone (29%). In each case, the prevalence of HHV-6 in LCH lesions was statistically significant, when compared to the control population. HSV DNA was not found in any of the LCH or control specimens. Although the presence of a virus alone does not establish a causal role in the disease, it supports the possibility of an etiologic relationship. From this study, we emphasize the need for further investigation of the potential HHV-6-mediated pathogenesis of LCH.