Specificity of StxB- and CtxB-induced VWF secretion. (A) Gb3 analog DAISY (μg/mL) was incubated with Stx1B, Stx2B (200 ng/mL), or histamine (100μM) before perfusion of HUVECs and quantification of VWF strings. (B) Wild-type Stx1B (■) and Stx1B W34A (□) were compared for ability to induce VWF string formation by HUVECs. Indicated comparisons between wild-type (wt) and W34A Stx1B are significant at P < .01 (**) by Student t test. (C) VWF string formation on HUVECs was assessed in response to recombinant Stx1B, anti-Gb3 IgM, or control mouse IgMκ antibody (Sigma-Aldrich); concentrations are in units of micrograms per milliliter. (D) VWF string formation on HUVECs in response Stx1B and CtxB at the indicated concentrations (μg/mL). (E) VWF string formation on HUVECs in response to CtxB (0.5 μg/mL) without or with anti-CtxB antibody (1 μg/mL). Experiments were performed at least 3 times with similar results. Values are shown as mean ± SE.