CD207CD1a cells circulate in pediatric patients with active Langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) is a rare disease with an unknown etiology characterized by heterogeneous lesions containing CD207CD1a cells that can arise in almost any tissue and cause significant morbidity and mortality. Precursors of pathological Langerhans cells have yet to be defined. Our aim was to identify circulating CD207CD1a cells and their inducers in LCH. Expression of CD207 and CD1a in the blood myeloid compartment as well as thymic stromal lymphopoietin (TSLP) and transforming growth factor β (TGF-β) plasma levels were measured in 22 pediatric patients with active disease (AD) or nonactive disease (NAD). In patients with AD vs those with NAD, the myeloid compartment showed an increased CD11b (CD11b plus CD11b) fraction (39.7 ± 3.6 vs 18.6 ± 1.9), a higher percentage of circulating CD11bCD11cCD207 cells (44.5 ± 11.3 vs 3.2 ± 0.5), and the presence of CD11cCD207CD1a cells (25.0 ± 9.1 vs 2.3 ± 0.5). Blood CD207CD1a cells were not observed in adult controls or umbilical cord. Increased TSLP and TGF-β levels were detected in patients with AD. Interestingly, plasma from patients with AD induces CD207 expression on CD14 monocytes. We conclude that CD207CD1a cells are circulating in patients with active LCH, and TSLP and TGF-β are potential drivers of Langerhans-like cells in vivo.