Elevated serum levels of the decoy receptor osteoprotegerin in children with Langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) is characterized by an accumulation of dendritic Langerhans cells in granulomatous lesions in the bone, skin, and other sites in the body. The pathogenesis of the disease remains unknown. We measured serum levels of the decoy receptor osteoprotegerin (OPG), an important regulator of bone metabolism as well as immune responses, in 18 children with single system (SS) or multi-system (MS) forms of LCH and 20 pediatric controls. OPG levels were significantly increased in LCH patients at diagnosis when compared with controls, and pretreatment levels of OPG were elevated in MS compared with SS patients. Moreover, OPG levels in LCH patients were elevated in patients with involvement of risk organs (liver, lungs, hematopoietic system, or spleen) when compared with patients without risk organ involvement, indicative of an association between OPG values and disease severity. We also observed a positive correlation between serum levels of OPG and tumor necrosis factor (TNF)-alpha, a pro-inflammatory cytokine, at the time of onset of disease. These findings show, for the first time, that serum OPG levels are elevated in LCH patients, and suggest that OPG may play a role in the pathogenesis of this enigmatic disease.