Induction of apoptosis and caspase activation in cells obtained from familial haemophagocytic lymphohistiocytosis patients.

Familial haemophagocytic lymphohistiocytosis (FHL) is a rare and uniformly fatal disorder of early childhood characterized by fever, hepatosplenomegaly, cytopenia and widespread infiltration of vital organs by activated lymphocytes and macrophages. In order to test whether the massive accumulation of immune cells in these patients is associated with a perturbation of apoptosis, lymphocytes were isolated from eight patients and subjected to the chemotherapeutic agent etoposide or agonistic anti-Fas monoclonal antibodies in vitro. These stimuli elicited a normal apoptotic response in FHL patient cells when compared to healthy controls, as determined by phosphatidylserine exposure, DNA fragmentation, in vitro cleavage of the caspase-3-like substrate aspartate-glutamate-valine-aspartate-7-amino-4-methyl-coumarin (DEVD-AMC) and proteolysis of the anti-apoptotic protein Bcl-2. In addition, the degree of constitutive and Fas-triggered apoptosis in freshly isolated neutrophils was monitored in three children, with similar results. These studies indicate that immune cells derived from FHL patients are not inherently resistant to apoptosis induction. Specifically, etoposide-induced and Fas-triggered activation of intracellular caspases appears to remain intact in these individuals. However, the degree of spontaneous activation of caspase-3-like enzymes in activated lymphocytes was attenuated in three of the four patients tested prior to initiation of therapy, suggesting a possible biological deficiency in these individuals.