Inhibition of active LFA-1 on DCs prevents the formation of prolonged contacts and rescues antigen-specific T-cell proliferation. Mature DCs from wild-type and LFA-1^d/d mice were left untreated or were pretreated with inhibitory antibodies directed against CD18 (GAME46) or CD11a (FD441.8), with a nonblocking CD18 antibody (M18/2) and an isotype control, respectively. Subsequently, DCs were pulsed with the ovalbumin peptide and cocultivated with naive CD4⁺ OT-II T cells in a 3-D collagen gel (ratio of 1 DC per 30 T cells). Contact times of individual T cells with wild-type versus LFA-1^d/d DCs (A) or DCs transfected with control or CYTIP-specific siRNA (C) were analyzed. Antigen-specific proliferation of CD4⁺ OT-II T cells was assessed by incorporation of [³H]thymidine (B,D). Assays were performed in triplicate. One representative assay of 3 is shown. ns indicates not significant.