Telomere Length Shortening in Langerhans Cell Histiocytosis.

The purpose of this study was to analyze telomere lengths in Langerhans Cell Histiocytosis (LCH). LCH is a clonally derived, proliferative disorder of phenotypically immature CD1a⁺ Langerhans cells (LCs). The etiology of LCH is unknown and data supporting an immune dysregulatory disorder as well as a clonal neoplasm have been reported. Telomere shortening has been associated with cancers and premalignant lesions as well as being important in promoting chromosomal instability. We therefore conducted a study to quantitatively determine the telomere lengths in LCH. Tissue arrays of reactive lymph nodes, local, multisystem, and systemic LCH containing 9, 7, 12, and 10 specimens respectively were used. These tissue arrays included 2 specimens that had unaffected skin represented, providing an opportunity to examine non-pathologic LCs. The tissue arrays were first hybridized with a N-terminal covalently linked Cy3-labeled, telomere specific peptide nucleic acid (PNA) probe to stain telomeres. The slides were then processed for indirect immunofluorescence to identify LCs using an anti-CD1a primary antibody followed by an anti-mouse IgG fraction Alexa Fluor 488. Finally, slides were counterstained with 4′-6-diamidino-2-phenylindole (DAPI). Digital fluorescent telomere signals were visualized using a Nikon Eclipse E400 epifluorescence microscope and telomere lengths were analyzed with ImageJ software. A total of 1039 measurements were made from 38 individuals. A significant shortening of telomeres was demonstrated in LCH LCs of local, multisystem and systemic LCH in comparison to telomere lengths of reactive lymph node LCs and normal skin, which were not significantly different. To investigate whether telomere length shortening of LCH LCs is selective, we analyzed the telomere length in lymphocytes in LCH specimens and in the reactive lymph node specimens. There was no significant evidence of telomere shortening of lymphocytes in LCH compared to lymphocytes in reactive lymph nodes (p=0.1862). These data show significant telomere shortening in the LCs in all stages of disease involvement with more variability among local cases. These observations suggest that in most cases LCH may share important mechanisms of telomere shortening and survival with clonal pre-neoplastic disorders and cancer.