Sera from patients with SCLS fail to induce endothelial apoptosis. (A) HMVEC monolayers were cultured in the presence (“basal”) or absence of growth factors or after adding staurosporine (1μM) overnight, followed by measurement of caspase 3/7 activities by luciferase assay. Data are mean ± SEM of ≥ 2 experiments measured in duplicate. (B) Growth factor–deprived HMVECs were incubated overnight with sera from healthy controls or patients with SCLS (basal or episodic) at 10% (vol/vol) concentrations. Data are mean ± SEM. (C-D) Same experiments as in panels A and B, except that growth factor–deprived cells were cultured with TNFα (1.25 ng/mL). Data are mean ± SEM; *P = .03, Mann-Whitney test.