Confocal microscopic appearance of biotinylated purified Bt 18 toxin-treated CEM-SS. CEM-SS cells were treated with fixed concentration of biotinylated purified Bt 18 toxin at various time intervals. The biotinylated toxin was then tagged with FITC-conjugated streptavidin (green). The biotinylated toxin was found at the periphery of treated CEM-SS cells. Increased binding of the biotinylated toxin was observed with increased incubation period. (A) Untreated negative control at 24 hours. (B) to (E) Treated cells at 1, 2, 12 and 24 hours respectively. Magnification: 630×. B = Biotinylated purified Bt 18 toxin, M = Cell membrane, N = Nucleus. Bar = 10 μm.