How stimulation of CD4⁺CD28^nullT cells in the presence of IL-12 affects the CD28 transcriptional initiator protein complex.

Stimulation of CD4⁺CD28^null T cells in the presence of IL-12 restores the CD28 transcriptional initiator protein complex. Nuclear extracts from CD4⁺CD28^nullT-cell clones and lines were analyzed by electrophoretic mobility shift assays for the presence of a protein complex binding to the INRα site of the CD28 gene.26 33 Binding activities were absent in anti-CD3 mAb– (a) or IL-12– (b) stimulated CD4⁺CD28^null T cells. The DNA binding activity was fully restored by costimulation with anti-CD3 mAb and IL-12 (c) and reached the level seen in CD28⁺ T cells. SP1 binding was used as a system control. One representative experiment of 4 is shown.