Contrasting effect of transforming growth factor type beta 1 (TGF-beta 1) on proliferation and interleukin-2 receptor expression in activated and rapidly cycling immature (CD3-CD4-CD8-) thymocytes

GARP Dampens Cancer Immunity by Sustaining Function and Accumulation of Regulatory T Cells in the Colon

Activated regulatory T (Treg) cells express the surface receptor glycoprotein-A repetitions predominant (GARP), which binds and activates latent TGFβ. How GARP modulates Treg function in inflammation and cancer remains unclear. Here we demonstrate that loss of GARP in Treg cells leads to spontaneous inflammation with highly activated CD4⁺ and CD8⁺ T cells and development of enteritis. Treg cells lacking GARP were unable to suppress pathogenic T-cell responses in multiple models of inflammation, including T-cell transfer colitis. GARP^-/- Treg cells were significantly reduced in the gut and exhibited a reduction in CD103 expression, a colon-specific migratory marker. In the colitis-associated colon cancer model, GARP on Treg cells dampened immune surveillance, and mice with GARP^-/- Treg cells exhibited improved antitumor immunity. Thus, GARP empowers the functionality of Treg cells and their tissue-specific accumulation, highlighting the importance of cell surface TGFβ in Treg function and GARP as a potential therapeutic target for colorectal cancer therapy.Significance: These findings uncover functions of membrane-bound TGFβ and GARP that tune the activity of Treg cells, highlighting a potential treatment strategy in autoimmune diseases and cancer.

Runx-dependent regulation of G-protein gamma3 expression in T-cells

Heterotrimeric G-proteins control diverse biological processes by conveying signals from seven-transmembrane receptors to intracellular effectors. Although their signaling roles were originally ascribed to their GTP-bound alpha-subunits, more recent evidence points to the equally active roles played by their betagamma-dimers. To elucidate the individual contributions of their gamma-subtypes, we used a gene targeting approach to show that mice lacking the gamma3-subtype display a defective T-cell dependent immune response. To identify the cellular basis for this defect, we demonstrated that gamma3-mRNA is strongly induced in activated CD4+ T-cells. To determine the mechanism for this regulated expression, we used several strategies to identify the importance of a Runx consensus sequence element in the first intron of the gamma3 gene and the Runx1 protein. Overall, these data provide the first genetic evidence for the tight regulation and involvement of the G protein gamma3-subtype in mounting an effective immune response in mice.

TGF-beta signaling in T cells: roles in lymphoid and epithelial neoplasia

Transforming growth factor-beta (TGF-beta) plays an essential role in regulating the homeostasis of cells in the lymphoid lineage. TGF-beta signaling is not required for normal thymopoiesis, but is essential for regulating the expansion, activation, and effector function of the mature CD4+ and CD8+ T cells in the peripheral lymphoid organs and target tissues. Recent studies in both mice and humans have elucidated an important and complex role for TGF-beta in regulatory T-cell biology. Disruption of TGF-beta signaling in T cells impairs the maintenance of regulatory T cells, results in the expansion of activated effector T cells, and is associated with the production of cytokines that have major effects on cells in their environment. While autoimmunity and inflammation are the principal phenotypes associated with the abrogation of TGF-beta signaling in T cells in mice, emerging evidence now also directly links Smad-dependent TGF-beta signaling in T cells to the suppression of epithelial neoplasia. The TGF-beta receptor-activated Smad3 plays a critical role in mediating many of the inhibitory effects of TGF-beta signaling in T cells, and has now been established as an important suppressor of leukemogenesis. These studies are increasing our awareness of the many complex mechanisms through which TGF-beta signaling controls the pathogenesis of cancer.

Embryonic age influences the capacity for cytokine induction in chicken thymocytes

Thymocyte responses to functional activation are of relevance to the evaluation of the efficacy of in ovo immunotherapies and vaccines in chickens. In this study we have demonstrated differences in chicken thymocyte responses according to developmental age. RNA samples from stimulated and unstimulated chicken thymocytes were assayed for messenger RNA encoding the cytokines interleukin-1beta (IL-1beta), IL-2, interferon-alpha (IFN-alpha), IFN-beta, IFN-gamma and transforming growth factor-beta4 (TGF-beta4), and also components of the major histocompatibility complex (MHC), beta2-microglobulin (beta2M) and the MHC class I alpha-chain (MHC IA). At embryonic day 14 thymocytes were least responsive to functional activation and differences existed even between thymocyte populations at embryonic day 18 and day 1 post-hatch. The duration of proliferation in response to stimulation was found to increase with increasing embryonic age. Mitogen stimulation of embryonic day 18 and day 1 post-hatch thymocytes induced up-regulation of IFN-gamma, IL-1beta and TGF-beta transcripts, and down-regulation of IFN-alpha, IFN-beta and IL-2 transcripts, with a higher induction of IFN-gamma, IL-1beta and TGF-beta transcripts in more immature T-cell-receptor-negative (TCR-) than TCR+ (TCR1+, TCR2+, or TCR3+) subsets. In contrast, in the mouse and human, both mature and immature thymocytes respond to mitogen stimulation with up-regulation of IL-2. Thymocytes from embryonic day 14 chicks responded to mitogen with a short burst of unsustained proliferation, and transcriptional down-regulation of the cytokines IL-2, IL-1beta, IFN-alpha, IFN-beta and IFN-gamma. These results suggest that embryonic day 14 thymocytes are largely unresponsive to mitogen. Transcripts encoding TGF-beta and type I interferons (IFN-alpha and IFN-beta) were constitutively expressed at high levels in very early thymocytes at embryonic day 14. Thymocytes at embryonic days 14 and 18 and day 1 post-hatch responded to mitogen stimulation with up-regulation of MHC IA transcript. The pattern of beta2M transcription following mitogen stimulation was distinct from that of the globally up-regulated MHC IA transcript, with up-regulation of beta2M transcription observed at embryonic day 18 and day 1 post-hatch but not at embryonic day 14. In thymocyte subsets, up-regulation of beta2M transcription was found to be specific to the CD8+ TCR+ population. The balance of responses in the embryonic thymus suggests that at all stages thymocytes have a reduced capacity for activation in comparison to mature thymocyte populations.

Divergent cell-specific effects of activin-A on thymocyte proliferation stimulated by phytohemagglutinin, and interleukin 1beta or interleukin 6 in vitro

Activin-A is a member of the transforming growth factor-beta (TGF-beta) cytokine family. Based on studies in several cell systems, activin-A has been postulated to be a specific inhibitor of the actions of the inflammatory cytokine, interleukin 6. In cultures of adult rat thymocytes, activin-A inhibited sub-optimal phytohemagglutinin-induced and interleukin 1beta-stimulated proliferation, as measured by [(3)H]-thymidine incorporation in vitro. In contrast with TGF-beta1, which exerted similar inhibitory effects on thymocyte proliferation, activin-A activity was reduced by increasing the concentration of phytohemagglutinin or addition of the reducing agent, beta-mercaptoethanol. Both activin-A and TGF-beta1 inhibited the in vitro production of interleukin 6 by thymocytes in the presence of phytohemagglutinin and interleukin 1beta. In the presence of exogenous interleukin 6, however, both activin-A and TGF-beta1 stimulated thymocyte proliferation. These data suggest that activin-A inhibits thymocyte growth and differentiation, at least in part, by inhibiting endogenous production of interleukin 6, but stimulates thymocyte growth when exogenous interleukin 6 is present in vitro. These data indicate that activin interacts with other cytokines to exert complex regulation of T cell development, and is not an inhibitor of interleukin 6 action in all cell systems.

Growth regulatory effects of transforming growth factor-beta 1 and interleukin-2 on IL-2 dependent CD4+T lymphoblastoid cell line

Transforming growth factor-beta 1 (TGF-beta 1) is an immuno-modulatory cytokine which has been shown to modulate the activity of T and B cells. We show here that human TGF-beta 1 inhibited stationary cultures of IL-2 dependent CD4+ bovine lymphoblastoid T cells (BLTC) by down-regulating their IL-2 receptor (IL-2R) expression, arresting cells in the G0/G1 compartment of the cell cycle, and inducing these cells to undergo apoptosis. These events were reversed by the addition of a minimal concentration of IL-2 (2U/ml). In the presence of exogenous IL-2, TGF-beta 1 was found to augment the proliferative response of BLTC through up-regulation of IL-2R expression, allow progression of normal cell cycle, and significantly prevent apoptosis. Our data clearly show that IL-2 and TGF-beta 1, when present alone, have contrasting effects on BLTC. TGF-beta 1 down regulates events that are associated with IL-2 mediated signal. But when present together, IL-2 and TGF-beta 1 upregulate activation signals and proliferation of rapidly dividing CD4+T cells.

Transforming growth factor beta 1 inhibits interleukin-1-induced but enhances ionomycin-induced interferon-gamma production in a T cell lymphoma: comparison with the effects of rapamycin

Transforming growth factor beta 1 (TGF-beta 1) is a multifunctional cytokine whose potent immunomodulatory activity is well documented. To explore the mechanisms of this activity we examined the effect of TGF-beta 1 on the production of IFN-gamma measured at the mRNA and protein levels in the YAC-1 T cell lymphoma. In previous studies, this model proved useful to characterize the mode of action of the immunosuppressant rapamycin (RAP). Here, we found that when induced by IL-1 or IL-1 + PMA, the production of IFN-gamma is suppressed by both TGF-beta 1 (ED50 = 1.9 pM) and RAP (ED50 = 0.2 nM). In contrast, when induced by the calcium ionophore ionomycin, in the absence or in the presence of PMA, this production is enhanced up to 10-fold by TGF-beta 1 (ED50 = 1.8 pM) and 1.5-3-fold by RAP. Therefore, in YAC-1 cells, TGF-beta 1 exerts opposite effects on IFN-gamma production depending on the mode of activation, and these effects parallel those of RAP. To further analyze the mode of action of TGF-beta 1 in this system, we used okadaic acid (OA), an inhibitor of serine/threonine protein phosphatases. Treatment with OA rendered the expression of IFN-gamma mRNA induced by IL-1 insensitive to TGF-beta 1 or RAP, indicating that activation of a phosphatase may play a role in the suppressive effect of both agents. However, OA did not prevent the augmentation of ionomycin-mediated induction of IFN-gamma mRNA by either TGF-beta 1 or RAP. Hence, the up-regulation of IFN-gamma production by TGF-beta 1 and RAP may involve a different biochemical mechanism than that mediating their suppressive action. These observations also favor the hypothesis that the two agents act on the same regulatory pathways. This was further supported by the finding that TGF-beta 1 and RAP modulate IFN-gamma production in an additive rather than synergistic fashion. However, their effects could be dissociated in mutants of YAC-1 cells selected for resistance to the inhibition of IL-1-mediated IFN-gamma induction by RAP. Moreover, the IFN-gamma modulatory action of RAP in YAC-1 cells was accompanied by an antiproliferative effect, whereas TGF-beta 1 failed to alter the growth of these cells. Therefore, the immunomodulatory action of TGF-beta 1 may result from the disruption of biochemical processes related to, although distinct from, those affected by RAP.