Dose-response curves for inhibitors.

(A) Dose-response curves of tetrapeptide aldehyde inhibitors of caspases 1 and 3 in the presence of 50 U/mL IFN-γ define the lowest concentrations that can be used in this assay to effectively and specifically block the suppressive effect of murine IFN-γ. (B) Murine FAC^−/− colony growth was enhanced by exposure to an inhibitor of caspase 3 (ac-DEVD-cho, 50 μmol/L) in IFN-treated cells. The difference in BFU-E production between dimethyl sulfoxide (DMSO) treatment alone and DMSO and IFN-γ treatment is statistically significant (P = .024 by Student t test), whereas the difference between treatment with DEVD-cho and Devd-cho and IFN-γ is not (P = .51). (C) Growth of IFN-exposed murine FAC^−/− hematopoietic progenitor cells was not enhanced by an inhibitor of caspase 1 (ac-YVAD-cho, 50 μmol/L). Colonies were expressed as percent control where control cells were cultured in medium containing appropriate dilutions of DMSO. All colony assays were performed on marrow cells cultured in the presence of murine Steel factor, murine interleukin 3, and human erythropoietin.