Active LFA-1 on DCs enhances the formation of long-lived contacts with naive T cells. Ovalbumin peptide–loaded mature wild-type (WT) or LFA-1^d/d DCs were cocultivated with untouched naive CD4⁺ OT-II (A) and CD8⁺ OT-I (C) T cells in 3-D collagen. Contact times of individual T-cell/DC pairs were analyzed during the first 12 hours of coculture. Numbers of contacts between DCs and CD4⁺ (B) and CD8⁺ (D) T cells that lasted longer than 60 minutes were counted.