Effect of saponin permeabilization on immunofluorescence.

Washed platelets were incubated with Stx1, and aggregates formed in the medium. In experiments in which immunofluorescence was performed in the presence of saponin, FITC staining was noted inside the aggregates for all concentrations of Stx1 (A, 1 ng/mL Stx1). In experiments in which immunofluorescence was assayed without saponin, FITC staining was noted on the periphery of aggregates. This was demonstrated for all concentrations of Stx1 (B, 1 ng/mL Stx1). Arrows indicate aggregates. Aggregates were identified as platelets by counterstaining with antibody to CD41-PE (not shown). Magnification, × 1000.