Effect of activation in the presence of IL-12 on transcription and re-expression of CD28 in CD4⁺CD28^null T cells.

CD4⁺CD28^null T cells transcribe and re-express CD28 when activated in the presence of IL-12. (A) CD4⁺CD28^null clones were activated with anti-CD3 mAb in the presence (+) or absence (−) of IL-12 (10 ng/mL), and the transcription of CD28 was analyzed by RT-PCR (clones 304I and 210I are shown). (B-F) Re-expression of CD28 was confirmed by flow cytometry. CD4⁺CD28^null T-cell clones (panels E-F) and lines (panel D) were stimulated with anti-CD3 mAb, IL-12, or a combination of anti-CD3 mAb and IL-12. Cells were analyzed by 4-color flow cytometry after 5 to 6 days; representative histograms are shown. The combination of anti-CD3 mAb and IL-12 induced CD28 expression in 5 of 11 lines and 6 of 13 clones. In contrast, the levels of CD28 expression were not affected in CD4⁺CD28⁺ T-cell clones or lines (panels B-C). In all histograms, the shaded areas represent staining with an isotype control.