Figure 1.

B7-1 expression on COS APCs provides efficient costimulatory signaling to naive CD4⁺ T cells. (A) Activation of naive CD4⁺ T cells upon contact with COS APCs loaded with HEL 48–63 peptides. 5 × 10⁵ naive CD4⁺ T cells from 3A9 TCRtg mice were cultured at 37°C with COS-A^k, COS-A^k/B7-1, COS-A^k/ICAM-1 cells, loaded or not with different doses of HEL 48–63. T cells were harvested after 20 h. IL-2 concentration in the supernatants was measured by ELISA. Data represented the mean of three individual experiments. Data: mean ± s.d. (B) Naive CD4⁺ T cells form mobile contacts with COS APCs loaded or not with HEL 48–63. Naive CD4⁺ T cells from 3A9 TCRtg mice were loaded onto APCs monolayers of COS-A^k, COS-A^k/B7-1, COS-A^k/ICAM-1 cells grown to confluency on Lab-Tek chamber slide, loaded or not with 1 μM HEL 48–63. T cell trajectories were recorded for 45 min at 37°C using confocal video-microscope. Average migration speed over the whole trajectory was calculated as described in Materials and Methods. Data: mean ± SEM. Their numerical values were 5.96 ± 0.21 μm/min (n = 105), 5.57 ± 0.24 μm/min (n = 56), 5.59 ± 0.18 μm/min (n = 111), 4.68 ± 0.11 μm/min (n = 134), 4.36 ± 0.23 μm/min (n = 60), and 4.36 ± 0.17 μm/min (n = 93) for the T cells contacting with COS-A^k, COS-A^k plus HEL 48–63, COS-A^k/B7-1, and COS-A^k/B7-1 plus HEL 48–63, COS-A^k/ICAM-1, and COS-A^k/ICAM-1 plus HEL 48–63, respectively. (C) Mean square displacement over time and (D) average mean square displacement over 10 min of T cells seeded onto COS-A^k, COS-A^k/B7-1, and COS-A^k/ICAM-1 cells, loaded or not with 1 μM HEL 48–63, respectively. Mann–Whitney tests were performed using Graphpad prism 7.0 for comparisons between two groups. Statistical significance was set at 0.05, and p-values < 0.05 were denoted in red. **p < 0.01, ***p < 0.001, and ****p < 0.0001.