Stimulation-dependent induction of CD154 on a subset of CD4+ FoxP3+ T-regulatory cells.

CD40-ligand/CD154 is predominantly expressed on activated CD4 T cells and plays a central role in regulating CD4 T-cell-dependent responses. To define the relative abilities of CD4 T-cell functional subsets in the induction of CD154--specifically FoxP3- effector, versus FoxP3+ regulatory, CD4 T cells--multiple CD4 T cell preparations were isolated from B6 and B6.FoxP3-GFP mice and stimulated in vitro to examine the kinetics of stimulation-dependent CD154 expression. CD154 was induced in 40-60% of total CD4 T cells in various cell preparations. However, despite similar kinetics of CD154-induced expression, the average percentage of CD154 expression among CD4+ FoxP3+ T regulatory (Treg) cells was only about 4-9%. Such differential, stimulation-dependent CD154 induction by total CD4+ T cells versus CD4+ FoxP3+ Treg cells was consistent, despite multiple stimulation conditions utilizing a variety of cell preparations of different composition. Similar induction of CD154 occurred irrespective of whether the CD4+ FoxP3+ Treg cells were first sorted to 98% purity and stimulated in vitro alone, or stimulated as non-purified cells in the presence of CD4+ FoxP3- T effector cells, suggesting that CD154 induction by CD4+ FoxP3+ Treg cells is regulated by cell-intrinsic mechanisms. Differential CD154 induction may be a key factor in determining the distinguishable functions of FoxP3- T-effector, versus FoxP3+ Treg, CD4+ T cells.