Penetrating dendrites and KCs retain TJ barrier function. Electron microscopy images of SC, SG cells, and dendrite tip of an LC. Keratohyalin granules (KH) identify SG1 cells. (A) Lanthanum permeability assay. Intercellular diffusion of lanthanum nitrate (electron-dense streak) is blocked at KC-KC TJs (arrow). (B) TJ-penetrated LC dendrite (asterisk) was found between the SG1 and SG2 cell layers. The junction between the LC dendrite and SG2 cells also inhibited lanthanum diffusion (arrows), suggesting an intact TJ barrier. Bars, 500 nm. (C) Enlarged image of the LC dendrite tip (B, asterisk), in which two of three Birbeck granules (arrows) were observed to generate from the cell membrane. Bar, 100 nm. (D) Schematic model for trans-TJ uptake activity of LCs. Activation of LCs induces elongation of LC dendrites beyond TJ barriers. bTJs and tTJs that are newly formed between LC and SG2 cells preserve the integrity of TJ barriers during this phenomenon. LCs access Ags that have violated the SC barrier in the presence of intact TJ barrier function. Schematics for gut intraepithelial DCs called lamina propria DCs are shown for comparison. Data presented in A–C is representative of two mice.