Confocal microscopic appearance of biotinylated purified Bt 18 toxin-treated human T lymphocytes. Human T lymphocytes 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). Biotinylated toxin was not found at all intervals except 24 hours, where the binding was very minimal. (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.