CTLA-4 ligation suppresses CD28-induced NF-kappa B and AP-1 activity in mouse T cell blasts

The effects of cytotoxic lymphocyte antigen 4 (CTLA-4) on CD3/CD28 monoclon al antibody (mAb) activation of CD4(+)/CTLA-4(+) blastoid T cells were stud ied in an in vitro model system. As previously reported, coligation of CTLA -4 mAb results in suppression of T cell proliferation and cytokine producti on. The proliferation but not the interleukin 2 (IL-2) production could be restored by addition of exogenous IL-2, suggesting that the inhibitory effe ct occurred at the level of IL-2 production rather than at the regulation o f the IL-2 receptor pathway. To study the effects on nuclear factors critic al for T cell activation, we analyzed the levels of the transcription facto rs NF-kappa B and AP-1. These were potently induced in CD3/CD28 mAb-restimu lated T cells. In contrast, CTLA-4 ligation strongly suppressed the inducti on of both transcription factors. The compositions of NF-kappa B and AP-1 f amily members were similar, irrespective of stimulation conditions. Analyse s of the NF-kappa B regulator I kappa B-alpha revealed similar levels of I kappa B-alpha protein in the preparations. However, a reduced phosphorylati on of I kappa B-alpha in CTLA-4 coengaged T cell blasts compared with T cel ls ligated with CD3/CD28 was-found. Previous studies have concluded that CT LA-4 ligation regulates T cell activation by inhibiting the T cell receptor -mediated signals, However, the present findings propose that the major imp act of CTLA-4 ligation is inhibition of signals mediated by CD28.