Sera from patients with SCLS elicit permeability of endothelial monolayers. (A) Migration of FITC-albumin across HMVEC monolayers was determined as outlined in “Methods” after adding medium that contained 5% serum from a patient with SCLS during an asymptomatic interval (“basal”) or during an acute attack (“episodic”) or sera pooled from healthy controls without SCLS (n = 8); *P = .02, 1-way ANOVA. (B-C) TEER of HMVEC monolayers after application of matched basal and episodic SCLS sera from 3 patients with SCLS. (C) Values are end point resistance values at 2.5 hours (mean ± SEM; *P < .03 and ***P = .0003, paired t test).