Immunofluorescent studies on COSdel.2-155 cells. Cells were preincubated on ice for 45 minutes with 24FM, washed, and exposed to 37°C for 0, 10, and 30 minutes (A, B, and C, respectively). After permeabilization and fixation, 24FM localization was identified as in Figs 3 and 4. Antibody-TM complex remained exclusively on the cell surface in these representative pictures (A, B, and C) over a 30-minute period. As with the COSdel.238 cells (Fig 4), there was no evidence of internalization or shedding of the complex.