T cells interact with DCs at the microvilli site. (A) Scanning electron micrographs recorded after a 4-hour coincubation of T cells and DCs. (Large panels) T cells bound to bundled DC microvilli. The bundle in the top panel is compact; in the bottom panel it is split, yet the T cell interacts with the microvilli. Bars represent 1 μm. Insets show entire cells demonstrating the disposition of veils and microvilli on DCs. (B) Transmission electron micrograph showing DC protrusions (→) consistent with the sections of microviilli at the DC–T-cell contact. Bars represent 2 μm (top panel) and 1 μm (bottom panel). (C) Distribution of intracellular actin (green, Alexa 488–conjugated phalloidin; see “Sample preparation for microscopy”) in a DC–T-cell pair. Actin density was higher at the perimeter of veils (arrows) and at the T cell–binding site (arrowhead). (D) Distribution of vasodilator-stimulated phosphoprotein (VASP; green, Alexa 488–conjugated to secondary antibody; “Sample preparation for microscopy”) in a DC interacting with a T cell. In panels C and D, nuclei were counterstained with Hoechst 33258 (blue). The T cell can be recognized by the round nucleus, smaller diameter, and lack of membrane extensions. Panels C and D each are composed of 2 stacked adjacent 1.0-μm-thick optical sections.