, 1998). In addition, the caspase-3-selective inhibitor, z-DEVD-FMK, which blocked T cell proliferation ( Alam et al., 1999), was subsequently shown to have little effect in other studies ( Boissonnas et al., 2002, Kennedy

et al., 1999 and Mack and Hacker, 2002). In the present study we examined the immunosuppressive properties of the peptidyl-FMK caspase inhibitors, z-VAD-FMK and z-IETD-FMK, and determined whether their inhibition of mitogen-induced T cell proliferation is due to the blocking of caspase processing during T cell activation. Our results showed that both caspase inhibitors readily block T cell proliferation induced by mitogens as well as IL-2. However, these peptidyl-FMK caspase inhibitors had little effect on the processing of caspase-8 and caspase-3 to their respective subunits during T cell activation although they efficiently Selinexor blocked caspase activation during apoptosis. Taken together, these results suggest that the inhibition of T cell proliferation mediated by these caspase inhibitors is independent of their caspase inhibition properties. Benzyloxycarbonyl-Val-Ala-Asp-(O-methyl)-fluoromehylketone (z-VAD-FMK), benzyloxycarbonyl-Ile-Glu-Thr-Asp-fluoromethylketone (IETD-FMK) Ivacaftor clinical trial and benzyloxycarbonyl-Phenyl-Alanyl-acid-fluoromethylketone (z-FA-FMK) were purchased from ICN (USA). Monoclonal antibody (mAb)

against CD3 (clone OKT3) was purified from hybridoma (ATCC) culture supernatants and anti-CD28 mAb was purchased from R & D (UK). Goat-anti caspase-8 was from Santa Cruz Biotechnology (USA) and rabbit anti-caspase-3 was generous gift from Xiao-Ming Sun, MRC Toxicology Unit (UK). FITC-conjugated anti-CD25 and RPE-conjugated anti-CD69 were acquired

from Transduction Laboratories (UK) and Dako (UK), respectively. Recombinant Fas ligand (FasL), anti-Flag and anti-PARP were obtained from Alexis PTK6 Biochemicals (UK). [3H]-thymidine was obtained from Amersham (UK) and phytohaemaglutinin (PHA) was purchased from Sigma (UK). MACS columns and MACS beads conjugated with anti-CD4 and anti-CD8 were obtained from Miltenyi Biotec (Germany). Lymphoprep was from Axis-Shield PoCAS (Norway) and RPMI 1640 and FCS were from Gibco (UK). Hoechst 33358 and carboxyfluorescein diacetate succinimidyl ester (CFSE) were from Molecular Probes (USA). Peripheral venous blood was obtained from normal healthy volunteers and collected into heparinized Vacutainers (Becton Dickinson). Peripheral blood mononuclear cells (PBMCs) were isolated using density gradient centrifugation with lymphoprep. The cells at the interface between the plasma and lymphoprep were collected, washed and re-suspended in RPMI containing 10% (v/v) foetal calf serum (FCS), 10 mM L-glutamine (Invitrogen, UK), penicillin (100 U/ml) and streptomycin (100 μg/ml).