T cells thus may be critical to LCH pathogenesis and indeed this has already been suggested for various reasons, such as the presence of cytokines suggestive of T cell activation (18, 19), and an enrichment of Foxp3+ regulatory T cells (Tregs), which are known for their immunosuppressive properties, within lesions (7-30% of total T cells) and blood from patients with active LCH (20, 21). Here, FOXP3 is linked to Langerhans cell histiocytosis.