Hemophagocytic lymphohistiocytosis (HLH) is characterized by hyperinflammation and multi-organ dysfunction. Infections, including the reactivation of viruses, contribute to significant disease mortality in HLH. While T and NK cell-driven immune activation and dysregulation are well described, limited data exist on the status of the B cell compartment and humoral immune function in HLH. We noted marked suppression of early B cell development in patients with active HLH. In vitro B …