Figure 1.

Distribution of IgA and FITC-dextran cointernalized from the apical pole of the cell for 2.5 min at 37°C (A–F) or with a 2.5-min pulse followed by a 7.5-min chase at 37°C (G–L). After IgA and FITC-dextran internalization, the cells were rapidly cooled, cell surface IgA was removed by trypsin treatment, and the cells were fixed with paraformaldehyde-lysine-periodate fixative. The fixed cells were incubated with IgA- and ZO1-specific primary antibodies and then reacted with CY5-labeled secondary antibodies. The CY5 signal is shown in the center panels, the FITC signal is shown in the left panels, and merged images of the CY5 and FITC signals are shown in the right panels. ZO1 appears as a thin red line at the periphery of each cell. Single optical sections, obtained with a confocal microscope, are shown from the apex of the cell (A–C and G–I) or at the level of the tight junctions (D–F and J–L). Note that the cells in the lower right corner of each panel, in panels G–L, are shorter than the cells in the upper left corner. Representative regions of colocalization are marked with arrows. Bars, 10 μm.