T-CVID T cells fail to up-regulate surface GM1. (A) Flow cytometric analysis of GM1 expression in PBL from the 4 patients with T-CVID (T-CVID1-4), 1 disease control patient (dis.ctr1), and 2 representative healthy controls (ctr; n = 4). Cells were activated for 27 hours by CD3/CD28 costimulation. Empty histogram shows the negative control (anti-CtxB and fluorochrome-labeled anti-mouse immunoglobulin; no CtxB). GM1 labeling in nonstimulated cells was not significantly higher than the negative control (not shown). Relative percentages of GM1⁺ cells and their mean fluorescence intensity are indicated. Results of representative experiments are shown (n ≥ 2). (B) Analysis of GM1 expression by confocal microscopy of PBL from patients with T-CVID (T-CVID1-4), 1 disease control patient (dis.ctr1), and 1 representative healthy control (ctr; n = 4). Cells were activated for 48 hours by CD3/CD28 costimulation or not (non act). Representative images are shown. Each experiment was performed 2 to 3 times.