Objective. CD4؉CD25؉ regulatory T cells (known asTreg

CD81 T lymphocytes are required for effective host defense against pathogens and also for mediating effector responses against uncontrolled proliferating self-tissues. In this study, we determine that individual CD8

BackgroundMigration of antigen-experienced T cells to secondary lymphoid organs and the site of antigenic-challenge is a mandatory prerequisite for the precise functioning of adaptive immune responses. The surface molecule CD152 (CTLA-4) is mostly considered as a negative regulator of T cell activation during immune responses. It is currently unknown whether CD152 can also influence chemokine-driven T cell migration.Methodology/Principal FindingsWe analyzed the consequences of CD152 signaling on Th cell migration using chemotaxis assays in vitro and radioactive cell tracking in vivo. We show here that the genetic and serological inactivation of CD152 in Th1 cells reduced migration towards CCL4, CXCL12 and CCL19, but not CXCL9, in a G-protein dependent manner. In addition, retroviral transduction of CD152 cDNA into CD152 negative cells restored Th1 cell migration. Crosslinking of CD152 together with CD3 and CD28 stimulation on activated Th1 cells increased expression of the chemokine receptors CCR5 and CCR7, which in turn enhanced cell migration. Using sensitive liposome technology, we show that mature dendritic cells but not activated B cells were potent at inducing surface CD152 expression and the CD152-mediated migration-enhancing signals. Importantly, migration of CD152 positive Th1 lymphocytes in in vivo experiments increased more than 200% as compared to CD152 negative counterparts showing that indeed CD152 orchestrates specific migration of selected Th1 cells to sites of inflammation and antigenic challenge in vivo.Conclusions/SignificanceWe show here, that CD152 signaling does not just silence cells, but selects individual ones for migration. This novel activity of CD152 adds to the already significant role of CD152 in controlling peripheral immune responses by allowing T cells to localize correctly during infection. It also suggests that interference with CD152 signaling provides a tool for altering the cellular composition at sites of inflammation and antigenic challenge.

Efficient adaptive immune responses require the localization of T lymphocytes in secondary lymphoid organs and inflamed tissues. To achieve correct localization of T lymphocytes, the migration of these cells is initiated and directed by adhesion molecules and chemokines. It has recently been shown that the inhibitory surface molecule CD152 (CTLA-4) initiates Th cell migration, but the molecular mechanism underlying this effect remains to be elucidated. Using CD4 T lymphocytes derived from OVA-specific TCR transgenic CD152-deficient and CD152-competent mice, we demonstrate that chemokine-triggered signal transduction is differentially regulated by CD152 via phosphoinositide 3-kinase (PI3K)-dependent activation of protein kinase B (PKB/Akt). In the presence of CD152 signaling, the chemoattractant CCL4 selectively induces the full activation of Akt via phosphorylation at threonine 308 and serine 473 in pro-inflammatory Th lymphocytes expressing the cognate chemokine receptor CCR5. Akt signals lead to cytoskeleton rearrangements, which are indispensable for migration. Therefore, this novel Akt-modulating function of CD152 signals affecting T cell migration demonstrates that boosting CD152 or its down-stream signal transduction could aid therapies aimed at sensitizing T lymphocytes for optimal migration, thus contributing to a precise and effective immune response.

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.

donors, Treg cell-depleted CD4ϩCD45ROϩ cells induced high amounts of CCL3 (mean Ϯ SEM 82.7 Ϯ 14.7 pg/ml), CCL17 (81.9 Ϯ 34.9 ng/ml), CCL19 (473.5 Ϯ 79.4 pg/ml), and CCL22 (116 Ϯ 27.4 ng/ml), Treg cells significantly inhibited the secretion of all of these chemokines (mean Ϯ SEM 15.7 Ϯ 4 pg/ml, 37.9 Ϯ 13.4 ng/ml, and 70.7 Ϯ 21.4 ng/ml for CCL3, CCL17, and CCL22, respectively, with CCL19 not induced at all). Thus, our results suggest that, in addition to suppressing T