Induction of anergy in Th1 cells associated with increased levels of cyclin-dependent kinase inhibitors p21(Cip1) and p27(Kip1)

Th1 cells exposed to Ag and the G(1) blocker n-butyrate in primary cultures lose their ability to proliferate in Ag-stimulated secondary cultures, The ability of n-butyrate to induce anergy in Ag-stimulated, but not resting, Th1 cells was shown here to be blocked by cycloheximide, Subsequent experim ents to delineate the nature of the protein apparently required for n-butyr ate-induced Th1 cell anergy focused on the role of cyclin-dependent kinase (cdk) inhibitors p21(Cip1) and p27(Kip1), Normally, entry into S phase by T h1 cells occurs around 24 h after Ag stimulation and corresponds with relat ively low levels of both p21(Cip1) and p27(Kip1). However, unlike control T h1 cells, anergic Th1 cells contained high levels of both p21(Cip1) and p27 (Kip1) when examined 24 h after Ag stimulation, The increase in p21(Cip1) o bserved in Ag-stimulated anergic Th1 cells appeared to be initiated in prim ary cultures, In contrast, the increase in p27(Kip1) observed in these aner gic Th1 cells appears to represent a re-expression of the protein much earl ier than control cells following Ag stimulation in secondary cultures. The anergic Th1 cells contained functionally active cdk inhibitors capable of i nhibiting the activity of both endogenous and exogenous cdks, Consequently, it appears that n-butyrate-induced anergy in Th1 cells correlated with the up-regulation of p21(Cip1) and perhaps the downstream failure to maintain low levels of p27(Kip1). Increased levels of both p21(Cip1) and p27(Kip1) a t the end of G(1) could prevent cdk-mediated entry into S phase, and thus h elp maintain the proliferative unresponsiveness found in the anergic Th1 ce lls.