Activities of NFκB, AP1, and Stat5 directly associated with the acquisition of CD80 by T cells. (A) Naive CD4⁺ T cells were cultured with either PCC-pulsed P13.9 fibroblasts (expressing high CD80) or PCC-pulsed DCEK fibroblasts (expressing low CD80) for 20 hours. Upon separation from APCs (0 hour), the T cells that acquired a high amount of CD80 (CD4⁺CD80^{acq hi}, left) or the T cells that acquired a low amount of CD80 (CD4⁺CD80^{acq low}, right) were further cultured in the absence of APCs and PCC peptide at various time points. Activity of NFκB, AP1, and Stat5 in CD4⁺CD80^{acq hi} (left) and CD4⁺CD80^{acq low} (right) T cells was measured using EMSA. (B) CD4⁺ T cells were stimulated with PCC peptide-pulsed macrophages for 20 hours. After the separation from macrophages, the activities of NFκB, AP1, and Stat5 in the CD4⁺CD80^acq T cells were measured using EMSA. (C) Naive CD4⁺ T cells were activated with either PCC-pulsed P13.9 (APCs) or anti-CD3 (10 μg/mL)/anti-CD28 (2 μg/mL) Abs for 20 hours. Upon separation from APCs or anti-CD3/anti-CD28 Abs (0 hour), these activated cells were further cultured in the absence of APCs, PCC peptide, or anti-CD3/anti-CD28 at various time points. The NFκB activity in these cells was analyzed using EMSA.