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CD28null T cells are a highly enriched subset of proinflammatory T cells in patients with autoimmune diseases that are oligoclonal and autoreactive. In this study, we analyzed the role of CD152 signaling on the longevity of human CD28null T cells. Using a sensitive staining method for CD152, we show that human CD4+CD28null and CD8+CD28null T cells rapidly express surface CD152. Serological inactivation of CD152 using specific Fab or blockade of CD152 ligands using CTLA-4Ig in CD4+CD28null and CD8+CD28null T cells enhances apoptosis in a Fas/FasL-dependent manner. CD152 cross-linking on activated CD28null cells prevents activation-induced cell death as a result of reduced caspase activity. Apoptosis protection conferred by CD152 is mediated by phosphatidylinositol 3′-kinase-dependent activation of the kinase Akt, resulting in enhanced phosphorylation and thereby inhibition of the proapoptotic molecule Bad. We show that signals triggered by CD152 act directly on activated CD28null T lymphocytes and, due to its exclusive expression as a receptor for CD80/CD86 on CD28null T cells, prevention of CD152-mediated signaling is likely a target mechanism taking place during therapy with CTLA-4Ig. Our data imply strongly that antagonistic approaches using CD152 signals for chronic immune responses might be beneficial.

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Polystyrene beads are broadly applied in flow cytometry. Implementing bead-based assays in mass cytometry is desired but hampered by the lack of an elemental label required for their detection. In this study, we introduce stable osmium tetroxide labeling as a universal approach for generating functionalized beads readily detectable by mass cytometry. We demonstrate the utility of osmium-labeled beads for signal spillover compensation in mass cytometry, and, strikingly, their application in quantitative Ab-binding capacity assays combined with high-dimensional profiling of human PBMC enabled the systematic assessment of receptor expression profiles across large numbers of cellular phenotypes. This analysis confirmed increased monocytic Siglec-1 expression in active systemic lupus erythematosus patients and, additionally, revealed interrelated reductions of CD4 expression by regulatory and memory CD4 T cells and HLA-DR expression by myeloid dendritic cells, pointing toward defective cross-talk at the immunological synapse that may limit immune responses in systemic lupus erythematosus. By converting conventional flow cytometry beads into beads suitable for mass cytometry, our approach paves the way toward the broad implementation of bead-based assays in high-dimensional cell profiling studies by mass cytometry in biomedical research.