The outcome of T-cell-mediated responses, immunity or tolerance, critically depends on the balance of cytopathic versus regulatory T (T reg ) cells. In the creation of stable tolerance to MHC incompatible allografts, reducing the unusually large mass of donorreactive cytopathic T effector (T eff ) cells via apoptosis is often required. Cyclosporine (CsA) blocks activationinduced cell death (AICD) of T eff cells, and is detrimental to tolerance induction by costimulation blockade, whereas Rapamycin (RPM) preserves AICD, and augments the potential of costimulation blockade to create tolerance. While differences between CsA and RPM in influencing apoptosis of activated graft-destructive T eff cells are apparent, their effects on graft-protective T reg cells remain enigmatic. Moreover, it is unclear whether tolerizing regimens foster conversion of naïve peripheral T cells into alloantigen-specific T reg cells for graft protection. Here we show, using reporter mice for T reg marker Foxp3, that RPM promotes de novo conversion of alloantigen-specific T reg cells, whereas CsA completely inhibits this process. Upon transfer, in vivo converted T reg cells potently suppress the rejection of donor but not third party skin grafts. Thus, the differential effects of RPM and CsA on T eff and T reg cells favor the use of RPM in shifting the balance of aggressive to protective type alloimmunity.

The common inhalation anesthetic isoflurane has been shown to induce apoptosis, which then leads to accumulation of ␤-amyloid protein, the hallmark feature of Alzheimer disease neuropathogenesis. The underlying molecular mechanism of the isoflurane-induced apoptosis is largely unknown. We, therefore, set out to assess whether isoflurane can induce apoptosis by regulating Bcl-2 family proteins, enhancing reactive oxygen species (ROS) accumulation, and activating the mitochondrial pathway of apoptosis. We performed these studies in cultured cells, primary neurons, and mice. Here we show for the first time that treatment with 2% isoflurane for 6 h can increase pro-apoptotic factor Bax levels, decrease antiapoptotic factor Bcl-2 levels, increase ROS accumulation, facilitate cytochrome c release from the mitochondria to the cytosol, induce activation of caspase-9 and caspase-3, and finally cause apoptosis as compared with the control condition. We have further found that isoflurane can increase the mRNA levels of Bax and reduce the mRNA levels of Bcl-2. The isoflurane-induced ROS accumulation can be attenuated by the intracellular calcium chelator BAPTA. Finally, the anesthetic desflurane does not induce activation of mitochondrial pathway of apoptosis. These results suggest that isoflurane may induce apoptosis through Bcl-2 family proteins-and ROS-associated mitochondrial pathway of apoptosis. These findings, which have identified at least partially the molecular mechanism by which isoflurane induces apoptosis, will promote more studies aimed at studying the potential neurotoxic effects of anesthetics.An estimated 200 million patients worldwide undergo anesthesia and surgery each year. Some clinical studies suggest that anesthesia and surgery may be associated with Alzheimer disease (AD) 3 (1-3), although different findings also exist (4, 5). Several recent studies have reported that isoflurane, one of the most commonly used inhalation anesthetics, may potentially contribute to AD neuropathogenesis by inducing apoptotic cell death and increasing ␤-amyloid protein oligomerization and accumulation in vitro and in vivo (6 -13). However, the upstream mechanism by which isoflurane induces apoptosis remains largely to be determined.Apoptosis is a programmed cell death which can be triggered by environmental and/or developmentally associated signals (14). The central components of the apoptosis process are a group of proteolytic enzymes called caspases, which can be activated by various types of stimulation (15). The extrinsic, death receptor pathway involves activation of caspase-8, which then cleaves caspase-3, leading to apoptosis (for review, see Ref. 16). The intrinsic, mitochondrial pathway is regulated by Bcl-2 family proteins, including the anti-apoptotic factor Bcl-2 and the pro-apoptotic factor Bax (for review, see Ref. 17) and involves cytochrome c release from the mitochondria to the cytosol. The released cytochrome c then activates caspase-9, which consequently induces caspase-3 activation, leading to apoptosi...