Stx1 uptake and activation of platelets.

(A) Unstimulated human platelets in medium incubated with monoclonal anti-Stx1 and goat-antimouse immunoglobulin FITC. No FITC labeling observed. (B) Same as in panel A, counterstained with mouse-antihuman CD41–PE to identify platelets. (C, D) Platelets incubated for 2 hours with 10 pg/mL Stx1 (C) or 10 ng/mL Stx1B (D). FITC labeling noted in cells. (E) Platelet aggregates forming after incubation with 100 pg/mL Stx1 labeled with mouse-antihuman CD41-PE (to identify platelets). (F) Platelet aggregates containing Stx1-FITC after incubation with 100 pg/mL Stx1 (same as panel E, labeled for Stx1). (G) Platelet aggregates containing Stx1B-FITC after incubation with 10 pg/mL Stx1B (combined labeling for FITC-Stx1 and anti-CD41–PE). (H) Preincubation of Stx1B (final concentration, 10 pg/mL; see “Patients, materials, and methods”) with anti-Stx1 inhibited the uptake of Stx1B and the formation of aggregates (FITC-Stx1 staining). (A-H) Magnification, × 400.