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Dendritic cells (DCs) are believed to regulate T cell-mediated immunity primarily by directing differentiation of naive T cells. Here, we show that a large fraction of CD4+ memory cells produce IL-10 within the first hours after interaction with plasmacytoid DCs (PDCs). In contrast, CD11c+ DCs induce IFN-γ and little IL-10. IL-10–secreting T cells isolated after 36 hours of culture with PDCs suppressed antigen-induced T-cell proliferation by an IL-10–dependent mechanism, but were distinct from natural and type 1 regulatory T cells. They proliferated strongly and continued to secrete IL-10 during expansion with PDCs, and after restimulation with immature monocyte-derived DCs or CD11c+ DCs. The IL-10–producing T cells acquired the ability to secrete high levels of IFN-γ after isolation and subsequent coculture with PDCs or CD11c+ DCs. Compared to CD11c+ DCs, PDCs were superior in their ability to selectively expand T cells that produced cytokines on repeated antigenic challenge. The DC-dependent differences in cytokine profiles were observed with viral recall antigen or staphylococcal enterotoxin B and were independent of extracellular type I interferon or IL-10. Our results show that DCs can regulate memory responses and that PDCs rapidly induce regulatory cytokines in effector T cells that can suppress bystander activity.

Caspase-3 is an intracellular cysteine protease, activated as part of the apoptotic response to cell injury. Its interest as a therapeutic target has led many to pursue the development of inhibitors. To date, only one series of nonpeptidic inhibitors have been described, and these have limited selectivity within the caspase family. Here we report the properties of a series of anilinoquinazolines (AQZs) as potent small molecule inhibitors of caspase-3. The AQZs inhibit human caspase-3 with Ki values in the 90 to 800 nM range. A subset of AQZs are equipotent against caspase-6, although most lack activity against this isoform and caspase-1, -2, -7, and -8. The AQZs inhibit endogenous caspase-3 activity toward a cell permeable, exogenously added substrate in staurosporine-treated SH-SY5Y cells. The AQZs reduce biochemical and cellular features of apoptosis that are thought to be a consequence of caspase-3 activation including DNA fragmentation, TUNEL staining, and the various morphological features that define the terminal stages of apoptotic cell death. Moreover, the AQZs also inhibit apoptosis induced by nerve growth factor withdrawal from differentiated PC12 cells. Thus, the AQZs represent a new and structurally novel class of inhibitors, some of which selectively inhibit caspase-3 and will thereby allow evaluation of the role of caspase-3 activity in various cellular models of apoptosis.

CD4⁺CD8^dim T cells represent a minor subset of the total CD3⁺ T cell population in peripheral blood. Although transient and persistent expansions of these cells havebeen reported in both healthy and diseased individuals, the functional properties of the CD4⁺CD8^dim population are largely unknown. In this study, we examined antigen-specific cytokine and proliferative responses of the CD4⁺CD8^dim subset. In whole blood cultures stimulated with the viral antigens HCMV and HIV-1, a significant fraction of the CD4⁺CD8^dim subset exhibited cytokine expression and proliferation in response to antigen activation. Typically, the CD4⁺CD8^dim population contained two- to eightfold higher frequencies of antigen-specific cytokine producing cells than the CD4⁺CD8^- population. Phenotypic analysis of the cytokine expressing CD4⁺CD8^dim population indicated that these cells are memory T cells, with a high frequency of this population expressing the cytotoxic markers CD56 and perforin. Furthermore, the CD4⁺CD8^dim cytokine responses to CMV were shown to be MHC class II dependent. Significantly, purified CD4⁺CD8^dim T cells were found to possess higher CMV-specific cytotoxic activity than purified CD4⁺CD8^– T cells in a standard ⁵¹Cr-release CTL assay. Thus, CD4⁺CD8^dim T cells appear to be MHC class II dependent, are capable of cytolytic effector activity, and are highly enriched within the CD4⁺ cell populations specific for HCMV and HIV-1.