TO THE EDITOR:

The thrombotic spectrum of antiphospholipid syndrome (APS) is heterogeneous and ranges from mild thrombosis in isolation to a catastrophic, multisystem disease, with thrombotic microangiopathy and organ failure. The exact mechanism of APS-related thrombosis remains to be elucidated and may differ between subsets of patients. Murine data have linked thrombosis, at least in part, to complement activation.1,2  Chaturvedi et al, in their interesting article in Blood, reported that patients’ serum induced C5b9 formation on human endothelial hybrid cells and corresponding complement-dependent cell killing (ie, modified Ham test). The authors argued that, with increasing severity of disease, the role of unrestrained complement activation via the alternative pathway becomes more dominant, as corroborated by the high prevalence of complement gene variants in catastrophic APS, quite like primary atypical hemolytic uremic syndrome (aHUS). Their data suggest that such patients...

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