Naive B cells strongly depend on a functional LFA-1-ICAM interaction for T-cell engagement. Naive and activated B cells or DCs were labeled with OVA, stained with SNARF, and coincubated with fresh CFSE-stained DO11.10 T cells in 96-well flat-bottom plates in the presence of different antibodies or cation chelators (A) or BIRT377, an inhibitor of LFA-1 activation (B-C). After 8 hours the cultures were fixed by PFA and analyzed for the formation of cell pairs by FACS. The absolute number of cell pairs without inhibition varied between 10% and 20%. The relative number of cell pairs in relation to the control (“Iso” or “no Inhib”) is shown. Data are means from at least 3 independent experiments. ^*P < .025; ^**P < .0004; n.s. = not significant. (D) Contact duration between DO11.10 T cells and naive B cells loaded with 100 μg/mL OVA was measured as described in Figure 2, albeit in the presence of 10 μg/mL BIRT377. Data were acquired over 16 hours after setting up of the culture. The horizontal bar indicates the median.