Consequently, a mechanism by which p21Cip1 binds to and inhibits AP-1 components should not block the ability of anergic Th1 cells to proliferate in response to exogenous IL-2 in secondary n-butyrate-free cultures. In contrast to anergic Th1 cells, Deforolimus there was no p21Cip1 in control Th1 cells before restimulation.

p21Cip1 gradually accumulated in the control Th1 cells, demonstrating very low levels at the early time periods at which p-JNK or p-c-jun were up-regulated in response to antigen restimulation. Therefore, in the control Th1 cells, early activation events were completed before p21Cip1 reached detectable levels, possibly explaining why p21Cip1 did not block initial cell division in control Th1 cells unlike the anergic Th1 cells. In the immunoprecipitation experiments, most of the JNK in the cell lysates did not associate with p21Cip1 except for a small amount in the anergic Th1 cells restimulated for 2 hr. Normally, only a small portion of JNK present in the cell becomes phosphorylated upon T-cell receptor stimulation. As the JNK antibody used in this study recognizes p-JNK as well as unphosphorylated JNK, the thin band of JNK that was associated with p21Cip1 in the restimulated anergic group could represent the phosphorylated form of JNK. p21Cip1 interaction with p-JNK and p-c-jun was demonstrated

in this study. It is not clear why p21Cip1 would bind preferentially to the phosphorylated forms of these FK228 order proteins, but phosphorylation-dependent confirmation changes may be in effect regulating this interaction. This interaction was confirmed in reciprocal immunoprecipitations. Unlike p21Cip1, p27Kip1 did not seem to associate with the MAPK in the anergic Th1 cells. p27Kip1 has been suggested to be a mediator of Adenosine T-cell tolerance in a study of human alloantigen-specific T-cell tolerance in which over-expression of p27Kip1 in primary cultures was shown to result in unresponsiveness in T-cell clones upon rechallenge in secondary cultures.3 In addition, p27Kip1 was recently shown to be required for transplantation tolerance induced

in vivo by costimulation blockade.38 Yet in one study, the role of p27Kip1 in T-cell anergy was questioned by investigators who showed that anti-TCR antibody could induce tolerance in p27Kip1-deficient CD4+ T cells in vitro.39 In our model, anergy induced by exposure to HDAC inhibitors, known to be potent stimulators of p21Cip1, seems to primarily rely on this CDK inhibitor rather than p27Kip1. The levels of p27Kip1 were not higher in the anergic Th1 cells than control Th1 cells at the end of 6-day primary cultures. p27Kip1 down-regulated rather than up-regulated in T cells treated with antigen and n-butyrate appeared to contradict reports in the literature describing an increase in p27Kip1 following exposure to n-butyrate.