IL-12, STAT4-dependent up-regulation of CD4(+) T cell core 2 beta-1,6-n-acetylglucosaminyltransferase, an enzyme essential for biosynthesis of P-selectin ligands

TCR activation of naive T cells in the presence of IL-12 drives polarization toward a Th1 phenotype and synthesis of P- and E-selectin ligands. Fucosyltransferase VII (Fuc-T VII) and core 2 beta-1,6-N-acetylglucosaminyltransferase (C2GnT) are critical for biosynthesis of selectin ligands. P-selectin glycoprotein ligand-1 is the best characterized ligand for P-selectin and also binds E-selectin. The contributions of TCR and cytokine signaling pathways to up-regulate Fuc-T VII and C2GnT during biosynthesis of E- and P-selectin ligands, such as P-selectin glycoprotein ligand 1, are unknown. IL-12 signals via the STAT4 pathway. Here, naive DO11.10 TCR transgenic and STAT4(-/-) TCR transgenic CD4(+) T cells were stimulated with Ag and IL-12 (Th1 condition), IL-4 (Th2), or neutralizing anti-IL-4 mAb only (Th0). The levels of Fuc-T VII and C2GnT mRNA in these cells were compared with their adhesive interactions with P- and E-selectin in vitro under flow. The data show IL-12/STAT4 signaling is necessary for induction of C2GnT, but not Fuc-TVII mRNA, and that STAT4(-/-) Th1 cells do not traffic normally to sites of inflammation in vivo, do not interact with P-selectin, and exhibit a partial reduction of E-selectin interactions under shear stress in vitro. Ag-specific TCR activation in CD4(+) T cells was sufficient to trigger induction of Fuc-TVII, but not C2GnT, mRNA and expression of E-selectin, but not P-selectin, ligands. Thus, Fuc-T VII and C2GnT are regulated by different signals during Th cell differentiation, and both cytokine and TCR signals are necessary for the expression of E- and P-selectin ligands.     

Modulation of O-glycans and N-glycans on murine CD8 T cells fails to alter annexin V ligand induction by galectin 1

Thymic negative selection and contraction of responding T cell oligoclones after infection represent important cell ablation processes required for maintaining T cell homeostasis. It has been proposed that galectin 1 contributes to these processes through interaction with lactosyl sequences principally on cell surface glycoproteins bearing core 2 (C2GnT1)-branched O-glycans. According to this model, specific T cell surface proteins cross-linked by galectin 1 induce signaling, ligand redistribution, and apoptosis in both immature thymocytes and activated T cells. The influence of lactosyl residues contained in branched O-glycans or complex N-glycans on galectin 1 binding and induction of annexin V ligand in murine CD8 T cells was assessed. Neither galectin binding nor galectin-induced expression of annexin V ligand was perturbed under conditions in which: 1) C2GnT1 activity was differentially induced by CD8 T cell activation/culture with IL-2 vs IL-4; 2) activated CD8(+) T cells lacked C2GnT1 expression; or 3) complex N-glycan formation was blocked by swainsonine. The maintenance of galectin 1 binding and induced annexin V expression under conditions that alter lactosamine abundance on O- or complex N-glycans suggest that galectin 1-mediated apoptosis is neither a simple function of fluctuating C2GnT1 activity nor a general C2GnT1-dependent mechanism underlying contraction of CD8 T cells subsequent to activation.     

P-selectin enhances generation of CD14+CD16+ dendritic-like cells and inhibits macrophage maturation from human peripheral blood monocytes

Endothelial cells play a critical role in monocyte differentiation. Platelets also affect terminal maturation of monocytes in vitro. P-selectin is an important adhesion molecule expressed on both endothelial cells and activated platelets. We investigated its effects on human peripheral blood monocyte differentiation under the influence of different cytokines. Generation of dendritic-like cells (DLCs) from peripheral blood monocytes was promoted by immobilized P-selectin in the presence of M-CSF and IL-4 as judged by dendritic cell (DC) morphology; increased expression of CD1a, a DC marker; low phagocytic activity; and high alloreactivity to naive T cells. In contrast to typical DCs, DLCs expressed CD14 and FcgammaRIII (CD16). These features link the possible identity of DLCs to that of an uncommon CD14(+)CD16(+)CD64(-) monocyte subset found to be expanded in a variety of pathological conditions. Functionally, DLCs generated by P-selectin in combination with M-CSF plus IL-4 primed naive allogeneic CD4(+) T cells to produce significantly less IFN-gamma than cells generated by BSA in the presence of M-CSF and IL-4. P-selectin effects on enhancing CD14(+)CD16(+) DLC generation were completely abrogated by pretreatment of cells with the protein kinase C delta inhibitor rottlerin, but not by classical protein kinase C inhibitor G?6976. Immobilized P-selectin also inhibited macrophage differentiation in response to M-CSF alone as demonstrated by morphology, phenotype, and phagocytosis analysis. The effects of P-selectin on macrophage differentiation were neutralized by pretreatment of monocytes with Ab against P-selectin glycoprotein ligand 1. These results suggest a novel role for P-selectin in regulating monocyte fate determination.     

Induction of CTL and nonpolarized Th cell responses by CD8alpha(+) and CD8alpha(-) dendritic cells

Two distinct dendritic cell (DC) subpopulations have been evidenced in mice on the basis of their differential CD8alpha expression and their localization in lymphoid organs. Several reports suggest that CD8alpha(+) and CD8alpha(-) DC subsets could be functionally different. In this study, using a panel of MHC class I- and/or class II-restricted peptides, we analyzed CD4(+) and CD8(+) T cell responses obtained after i.v. injection of freshly purified peptide-pulsed DC subsets. First, we showed that both DC subsets efficiently induce specific CTL responses and Th1 cytokine production in the absence of CD4(+) T cell priming. Second, we showed that in vivo activation of CD4(+) T cells by CD8alpha(+) or CD8alpha(-) DC, injected i.v., leads to a nonpolarized Th response with production of both Th1 and Th2 cytokines. The CD8alpha(-) subset induced a higher production of Th2 cytokines such as IL-4 and IL-10 than the CD8alpha(+) subset. However, IL-5 was produced by CD4(+) T cells activated by both DC subsets. When both CD4(+) and CD8(+) T cells were primed by DC injected i.v., a similar pattern of cytokines was observed, but, under these conditions, Th1 cytokines were mainly produced by CD8(+) T cells, while Th2 cytokines were produced by CD4(+) T cells. Thus, this study clearly shows that CD4(+) T cell responses do not influence the development of specific CD8(+) T cell cytotoxic responses induced either by CD8alpha(+) or CD8alpha(-) DC subsets.     

CD45 modulates galectin-1-induced T cell death: regulation by expression of core 2 O-glycans.

Galectin-1 induces death of immature thymocytes and activated T cells. Galectin-1 binds to T cell-surface glycoproteins CD45, CD43, and CD7, although the precise roles of each receptor in cell death are unknown. We have determined that CD45 can positively and negatively regulate galectin-1-induced T cell death, depending on the glycosylation status of the cells. CD45(+) BW5147 T cells lacking the core 2 beta-1,6-N-acetylglucosaminyltransferase (C2GnT) were resistant to galectin-1 death. The inhibitory effect of CD45 in C2GnT(-) cells appeared to require the CD45 cytoplasmic domain, because Rev1.1 cells expressing only CD45 transmembrane and extracellular domains were susceptible to galectin-1 death. Moreover, treatment with the phosphotyrosine-phosphatase inhibitor potassium bisperoxo(1,10-phenanthroline)oxovanadate(V) enhanced galectin-1 susceptibility of CD45(+) T cell lines, but had no effect on the death of CD45(-) T cells, indicating that the CD45 inhibitory effect involved the phosphatase domain. Expression of the C2GnT in CD45(+) T cell lines rendered the cells susceptible to galectin-1, while expression of the C2GnT in CD45(-) cells had no effect on galectin-1 susceptibility. When CD45(+) T cells bound to galectin-1 on murine thymic stromal cells, only C2GnT(+) T cells underwent death. On C2GnT(+) cells, CD45 and galectin-1 co-localized in patches on membrane blebs while no segregation of CD45 was seen on C2GnT(-) T cells, suggesting that oligosaccharide-mediated clustering of CD45 facilitated galectin-1-induced cell death.     

Functional role of P-selectin glycoprotein ligand 1/P-selectin interaction in the generation of tolerogenic dendritic cells

Dendritic cells (DCs) have a key role in both the generation of the immune response and the induction of tolerance to self-Ags. In this work, the possible role of P-selectin glycoprotein ligand 1 (PSGL-1) on the tolerogenic activity of human DCs was explored. We found that the engagement of PSGL-1 by P-selectin on DCs induced the expression of c-Fos, IDO, IL-10, and TGF-beta genes. Remarkably, stimulation of DCs through PSGL-1 with P-selectin enhanced their capability to generate CD4(+)CD25(+)Foxp3(+) regulatory T cells, which expressed high levels of TGF-beta1 mRNA, synthesized IL-10, and suppressed the proliferation of autologous CD4(+)CD25(-) T cells. Accordingly, we found that DCs from PSGL-1(-/-) mice expressed higher levels of MHC class II molecules, and exhibited an enhanced immunogenicity compared with wild-type mice. In addition, the percentage of CD4(+)CD25(+)Foxp3(+) regulatory T cells in the thymus of PSGL-1-deficient animals was significantly reduced. Our data reveal an unexpected role of PSGL-1 on the tolerogenic function of DCs, and the regulation of the immune response.     

Differential regulation of killer cell lectin-like receptor G1 expression on T cells

The killer cell lectin-like receptor G1 (KLRG1) is the mouse homologue of the rat mast cell function-associated Ag and contains a tyrosine-based inhibitory motif in its cytoplasmic domain. It has been demonstrated that KLRG1 is induced on activated NK cells and that KLRG1 can inhibit NK cell effector functions. In this study, we show that in naive C57BL/6 mice KLRG1 is expressed on a subset of CD44(high)CD62L(low) T cells. KLRG1 expression can be detected on a small number of V(alpha)14i NK T cells but not on CD8alphaalpha(+) intraepithelial T cells that are either TCRgammadelta(+) or TCRalphabeta(+). We also show that KLRG1 expression is dramatically induced on approximately 50% of the CD8(+) T cells during both a viral and a parasitic infection. Interestingly, during Toxoplasma gondii infection, KLRG1 is up-regulated on CD4(+) T cells. Although KLRG1 expression can be induced on both NK cells and T cells, the molecular mechanism leading to the induction of KLRG1 differs in these two subsets of cells. Indeed, the up-regulation of KLRG1 on NK cells can be driven in vivo by cytokines, whereas KLRG1 cannot be induced on CD8(+) T cells by cytokines. In addition, although induction of KLRG1 on T cells appears to require TCR engagement in vivo, TCR engagement is not sufficient for KLRG1 induction in vitro. Taken together, these data suggest that the expression and induction of KLRG1 on T cells are tightly regulated. This could have important biological consequences on T cell activation and homeostasis.     

Notch-ligand expression by NALT dendritic cells regulates mucosal Th1- and Th2-type responses

Our previous studies showed that an adenovirus (Ad) serotype 5 vector expressing Flt3 ligand (Ad-FL) as nasal adjuvant activates CD11c(+) dendritic cells (DCs) for the enhancement of antigen (Ag)-specific IgA antibody (Ab) responses. In this study, we examined the molecular mechanism for activation of CD11c(+) DCs and their roles in induction of Ag-specific Th1- and Th2-cell responses. Ad-FL activated CD11c(+) DCs expressed increased levels of the Notch ligand (L)-expression and specific mRNA. When CD11c(+) DCs from various mucosal and systemic lymphoid tissues of mice given nasal OVA plus Ad-FL were cultured with CD4(+) T cells isolated from non-immunized OVA TCR-transgenic (OT II) mice, significantly increased levels of T cell proliferative responses were noted. Furthermore, Ad-FL activated DCs induced IFN-γ, IL-2 and IL-4 producing CD4(+) T cells. Of importance, these APC functions by Ad-FL activated DCs were down-regulated by blocking Notch-Notch-L pathway. These results show that Ad-FL induces CD11c(+) DCs to the express Notch-ligands and these activated DCs regulate the induction of Ag-specific Th1- and Th2-type cytokine responses.     

Activation pathways implicate anti-HLA-DP and anti-LFA-1 antibodies as lead candidates for intervention in chronic berylliosis

CD4(+) T cells play a key role in granulomatous inflammation in the lung of patients with chronic beryllium disease. The goal of this study was to characterize activation pathways of beryllium-responsive bronchoalveolar lavage (BAL) CD4(+) T cells from chronic beryllium disease patients to identify possible therapeutic interventional strategies. Our results demonstrate that in the presence of APCs, beryllium induced strong proliferation responses of BAL CD4(+) T cells, production of superoptimal concentrations of secreted proinflammatory cytokines, IFN-gamma, TNF-alpha,and IL-2, and up-regulation of numerous T cell surface markers that would promote T-T Ag presentation. Ab blocking experiments revealed that anti-HLA-DP or anti-LFA-1 Ab strongly reduced proliferation responses and cytokine secretion by BAL CD4(+) T cells. In contrast, anti-HLA-DR or anti-OX40 ligand Ab mainly affected beryllium-induced proliferation responses with little impact on cytokines other than IL-2, thus implying that nonproliferating BAL CD4(+) T cells may still contribute to inflammation. Blockade with CTLA4-Ig had a minimal effect on proliferation and cytokine responses, confirming that activation was independent of B7/CD28 costimulation. These results indicate a prominent role for HLA-DP and LFA-1 in BAL CD4(+) T cell activation and further suggest that specific Abs to these molecules could serve as a possible therapy for chronic beryllium disease.     

Low-dose tolerance is mediated by the microfold cell ligand, reovirus protein sigma1

Mucosal tolerance induction generally requires multiple or large Ag doses. Because microfold (M) cells have been implicated as being important for mucosal tolerance induction and because reovirus attachment protein sigma1 (psigma1) is capable of binding M cells, we postulated that targeting a model Ag to M cells via psigma1 could induce a state of unresponsiveness. Accordingly, a genetic fusion between OVA and the M cell ligand, reovirus psigma1, termed OVA-psigma1, was developed to enhance tolerogen uptake. When applied nasally, not parenterally, as little as a single dose of OVA-psigma1 failed to induce OVA-specific Abs even in the presence of adjuvant. Moreover, the mice remained unresponsive to peripheral OVA challenge, unlike mice given multiple nasal OVA doses that rendered them responsive to OVA. The observed unresponsiveness to OVA-psigma1 could be adoptively transferred using cervical lymph node CD4(+) T cells, which failed to undergo proliferative or delayed-type hypersensitivity responses in recipients. To discern the cytokines responsible as a mechanism for this unresponsiveness, restimulation assays revealed increased production of regulatory cytokines, IL-4, IL-10, and TGF-beta1, with greatly reduced IL-17 and IFN-gamma. The induced IL-10 was derived predominantly from FoxP3(+)CD25(+)CD4(+) T cells. No FoxP3(+)CD25(+)CD4(+) T cells were induced in OVA-psigma1-dosed IL-10-deficient (IL-10(-/-)) mice, and despite showing increased TGF-beta1 synthesis, these mice were responsive to OVA. These data demonstrate the feasibility of using psigma1 as a mucosal delivery platform specifically for low-dose tolerance induction.     

Modulation by IL-2 of CD70 and CD27 expression on CD8+ T cells: importance for the therapeutic effectiveness of cell transfer immunotherapy

Proper T cell function relies on the integration of signals delivered by Ag, cytokine, and costimulatory receptors. In this study, the interactions between IL-2, CD27, and its ligand CD70 and their effects on human T cell function were examined. Unstimulated CD8(+) T cells expressed relatively low levels of CD70 and high levels of CD27. Incubation in vitro with high doses of IL-2 (3,000 IU/ml) or administration of IL-2 in vivo resulted in substantial up-regulation of CD70 expression and the concomitant loss of cell surface CD27 expression on CD8(+) cells. Withdrawal of IL-2 from activated CD8(+) T cells that had been maintained in IL-2 resulted in a reversal of the expression of these two markers, whereas reciprocal changes were seen following treatment of PBMCs with IL-2. The proliferation observed in cells stimulated with IL-2 primarily occurred in a subset of the CD70(+)CD8(+) T cells that up-regulated IL-2 receptor expression but did not occur in CD70(-)CD8(+) T cells. Blocking CD70 resulted in a significant reduction of T cell proliferation induced by high-dose IL-2, indicating that the interaction of CD70 with CD27 played a direct role in T cell activation mediated by IL-2. Finally, studies conducted on tumor-infiltrating lymphocyte (TIL) samples that were administered to melanoma patients indicated that the size of the pool of CD27(+)CD8(+) T cells in bulk TILs was highly associated (p = 0.004) with the ability of these TILs to mediate tumor regression following adoptive transfer.     

CD209(+) macrophages mediate host defense against Propionibacterium acnes

Propionibacterium acnes is a major etiological factor of acne, triggering an inflammatory response in part through the activation of TLR2. In this study, we demonstrate that activation of peripheral blood monocytes with P. acnes in vitro induced their differentiation into two distinct innate immune cell subsets, CD209(+) macrophages and CD1b(+) dendritic cells. Furthermore, P. acnes induced expression of mRNA for the cytokines IL-15 and GM-CSF, which differentiate CD209(+) and CD1b(+) cells, respectively. The CD209(+) cells were more effective in uptake of P. acnes, compared with the CD1b(+) cells, and demonstrated a 2-fold greater antimicrobial activity against the phagocytosed bacteria. Although CD1b(+) cells secreted inflammatory cytokines in response to both P. acnes and a TLR2 ligand control, the CD209(+) cells responded only to P. acnes. The addition of all-trans retinoic acid, a commonly used agent for the treatment of acne, directly induced differentiation of monocytes into CD209(+) macrophages and enhanced the P. acnes-mediated differentiation of the CD209(+) subset. Therefore, the differentiation of monocytes into CD209(+) macrophages and CD1b(+) dendritic cells distinctly mediate the innate immune response to P. acnes.     

Impaired TCR-mediated induction of Ki67 by naive CD4+ T cells is only occasionally corrected by exogenous IL-2 in HIV-1 infection

Perturbations in naive T cell homeostasis and function may play a major role in the immunodeficiency that accompanies HIV infection. By examining naive CD4(+) T cell function on a single cell basis, we provide evidence that these cells have significant qualitative defects in HIV disease. Ki67, a molecule expressed during cell cycle progression, is induced less efficiently among naive CD4(+) T cells from HIV-infected individuals following activation with anti-TCR Ab. The impairment in Ki67 expression is evident even when a separate function, CD62L down-modulation, is within normal ranges. Moreover, the defects in Ki67 induction are only sometimes corrected by the addition of rIL-2 to cell cultures. An initial assessment of IL-2 unresponsiveness in cells from selected HIV-infected individuals suggests that the defect is not a consequence of impaired IL-2R expression or IL-2R signaling capability. Qualitative defects in naive T cells that cannot be routinely corrected by IL-2 have significant implications for disease pathogenesis and for strategies using IL-2 as a vaccine adjuvant in HIV disease.     

Antigen-independent induction of Tim-3 expression on human T cells by the common γ-chain cytokines IL-2, IL-7, IL-15, and IL-21 is associated with proliferation and is dependent on the phosphoinositide 3-kinase pathway

T cell Ig mucin domain-containing molecule 3 (Tim-3) is a glycoprotein found on the surface of a subset of CD8(+) and Th1 CD4(+) T cells. Elevated expression of Tim-3 on virus-specific T cells during chronic viral infections, such as HIV-1, hepatitis B virus, and hepatitis C virus, positively correlates with viral load. Tim-3(+) cytotoxic T cells are dysfunctional and are unable to secrete effector cytokines, such as IFN-γ and TNF-α. In this study, we examined potential inducers of Tim-3 on primary human T cells. Direct HIV-1 infection of CD4(+) T cells, or LPS, found to be elevated in HIV-1 infection, did not induce Tim-3 on T cells. Tim-3 was induced by the common γ-chain (γc) cytokines IL-2, IL-7, IL-15, and IL-21 but not IL-4, in an Ag-independent manner and was upregulated on primary T cells in response to TCR/CD28 costimulation, as well as γc cytokine stimulation with successive divisions. γc cytokine-induced Tim-3 was found on naive, effector, and memory subsets of T cells. Tim-3(+) primary T cells were more prone to apoptosis, particularly upon treatment with galectin-9, a Tim-3 ligand, after cytokine withdrawal. The upregulation of Tim-3 could be blocked by the addition of a PI3K inhibitor, LY 294002. Thus, Tim-3 can be induced via TCR/CD28 costimulation and/or γc cytokines, likely through the PI3K pathway.     

Phagocytosis, a potential mechanism for myeloid-derived suppressor cell regulation of CD8+ T cell function mediated through programmed cell death-1 and programmed cell death-1 ligand interaction

CD8(+) T cells become exhausted, inducing cell surface protein programmed cell death-1 (PD-1) as chronic virus diseases or tumors progress, but underlying mechanisms of this are unclear. We previously showed that M-CSF is important for developing tolerogenic dendritic cells (DCs) from human CD14(+) monocytes. In this article, we identify M-CSF-derived DCs (M-DCs) after stimulation with IL-10 as myeloid-derived suppressor cells with additional tolerogenic activities to CD8(+) T cells. IL-10 increased PD-1 ligand expression on M-DC, and IL-10-stimulated M-DCs (M-DC/IL-10) induced expression of PD-1 on, and apoptosis of, CD8(+) T cells and phagocytosed CD8(+) T cells. Enhanced phagocytic activity of M-DC/IL-10 required IFN-γ, which further increased PD-1 ligand and PD-2 ligand expression on M-DC/IL-10. IFN-γ-stimulated M-DC/IL-10 cells were phenotypically macrophage-like cells with little or no expression of CD86, a costimulatory molecule, but with high expression levels of CD14, CD200R, and CD80. No phagocytic activity was detected with GM-CSF-derived DCs. We propose that phagocytosis by IFN-γ-stimulated M-DC/IL-10 cells, which may be DCs or, alternatively, a unique subset of macrophages, may be a mechanism by which IFN-γ-producing CD8(+) T cells are tolerized after type 1 immune responses to chronic virus or tumor, and that IFN-γ links effector CD8(+) T cells to their phagocytic clearance.     

Selective expansion and partial activation of human NK cells and NK receptor-positive T cells by IL-2 and IL-15.

IL-2 and IL-15 are lymphocyte growth factors produced by different cell types with overlapping functions in immune responses. Both cytokines costimulate lymphocyte proliferation and activation, while IL-15 additionally promotes the development and survival of NK cells, NKT cells, and intraepithelial lymphocytes. We have investigated the effects of IL-2 and IL-15 on proliferation, cytotoxicity, and cytokine secretion by human PBMC subpopulations in vitro. Both cytokines selectively induced the proliferation of NK cells and CD56(+) T cells, but not CD56(-) lymphocytes. All NK and CD56(+) T cell subpopulations tested (CD4(+), CD8(+), CD4(-)CD8(-), alphabetaTCR(+), gammadeltaTCR(+), CD16(+), CD161(+), CD158a(+), CD158b(+), KIR3DL1(+), and CD94(+)) expanded in response to both cytokines, whereas all CD56(-) cell subpopulations did not. Therefore, previously reported IL-15-induced gammadelta and CD8(+) T cell expansions reflect proliferations of NK and CD56(+) T cells that most frequently express these phenotypes. IL-15 also expanded CD8alpha(+)beta(-) and Valpha24Vbeta11 TCR(+) T cells. Both cytokines stimulated cytotoxicity by NK and CD56(+) T cells against K562 targets, but not the production of IFN-gamma, TNF-alpha, IL-2, or IL-4. However, they augmented cytokine production in response to phorbol ester stimulation or CD3 cross-linking by inducing the proliferation of NK cells and CD56(+) T cells that produce these cytokines at greater frequencies than other T cells. These results indicate that IL-2 and IL-15 act at different stages of the immune response by expanding and partially activating NK receptor-positive lymphocytes, but, on their own, do not influence the Th1/Th2 balance of adaptive immune responses.     

Signaling events involved in interleukin 27 (IL-27)-induced proliferation of human naive CD4+ T cells and B cells

IL-27 induces stronger proliferation of naive than memory human B cells and CD4(+) T cells. In B cells, this differential response is associated with similar levels of IL-27 receptor chains, IL-27Rα and gp130, in both subsets and stronger STAT1 and STAT3 activation by IL-27 in naive B cells. Here, we show that the stronger proliferative response of CD3-stimulated naive CD4(+) T cells to IL-27 is associated with lower levels of IL-27Rα but higher levels of gp130 compared with memory CD4(+) T cells. IL-27 signaling differs between naive and memory CD4(+) T cells, as shown by more sustained STAT1, -3, and -5 activation and weaker activation of SHP-2 in naive CD4(+) T cells. In the latter, IL-27 increases G0/G1 to S phase transition, cell division and, in some cases, cell survival. IL-27 proliferative effect on naive CD4(+) T cells is independent of MAPK, but is dependent on c-Myc and Pim-1 induction by IL-27 and is associated with induction of cyclin D2, cyclin D3, and CDK4 by IL-27 in a c-Myc and Pim-1-dependent manner. In BCR-stimulated naive B cells, IL-27 only increases entry in the S phase and induces the expression of Pim-1 and of cyclins A, D2, and D3. In these cells, inhibition of Pim-1 inhibits IL-27 effect on proliferation and cyclin induction. Altogether, these data indicate that IL-27 mediates proliferation of naive CD4(+) T cells and B cells through induction of both common and distinct sets of cell cycle regulators.     

A novel costimulation pathway via the 4C8 antigen for the induction of CD4+ regulatory T cells

CD4(+)CD25(+) regulatory T (Treg) cells naturally occur in mice and humans, and similar Treg cells can be induced in vivo and in vitro. However, the molecular mechanisms that mediate the generation of these Treg cell populations remain unknown. We previously described anti-4C8 mAbs that inhibit the postadhesive transendothelial migration of T cells through human endothelial cell monolayers. We demonstrate in this work that Treg cells are induced by costimulation of CD4(+) T cells with anti-CD3 plus anti-4C8. The costimulation induced full activation of CD4(+) T cells with high levels of IL-2 production and cellular expansion that were comparable to those obtained on costimulation by CD28. However, upon restimulation, 4C8-costimulated cells produced high levels of IL-10 but no IL-2 or IL-4, and maintained high expression levels of CD25 and intracellular CD152, as compared to CD28-costimulated cells. The former cells showed hyporesponsiveness to anti-CD3 stimulation and suppressed the activation of bystander T cells depending on cell contact but not IL-10 or TGF-beta. The suppressor cells developed from CD4(+)CD25(-)CD45RO(+) cells. The results suggest that 4C8 costimulation induces the generation of Treg cells that share phenotypic and functional features with CD4(+)CD25(+) T cells, and that CD25(-) memory T cells may differentiate into certain Treg cell subsets in the periphery.