Search

Unmethylated CpG-oligodeoxynucleotides (ODNs) are generally thought of as potent adjuvants with considerable therapeutic potential to enhance immune responses against microbes and tumors. Surprisingly, certain so-called stimulatory CpG-ODNs strongly inhibited the effector phase of inflammatory arthritis in the K/BxN serum transfer system, either preventively or therapeutically. Also unexpected was that the inhibitory influence did not depend on the adaptive immune system cells mobilized in an immunostimulatory context. Instead, they relied on cells of the innate immune system, specifically on cross talk between CD8α+ dendritic cells and natural killer cells, resulting in suppression of neutrophil recruitment to the joint, orchestrated through interleukin-12 and interferon-γ. These findings highlight potential applications of CpG-ODNs and downstream molecules as antiinflammatory agents.

Mice deficient in the E3 ubiquitin ligase Cbl-b have CD28-independent T cells and develop autoimmunity. We previously reported that Cbl-b−/− CD4+CD25− T effector cells are resistant in vitro to the antiproliferative effects of CD4+CD25+ regulatory T cells and TGF-β. We have now asked whether the resistance noted in Cbl-b−/− T cells is restricted solely to TGF-β’s antiproliferative effects, whether the TGF-β resistance has in vivo relevance, and whether a defect can be identified in the TGF-β signaling pathway. We now demonstrate the following: 1) in vitro, Cbl-b deficiency prevents the TGF-β-mediated induction of Foxp3+ functional regulatory T cells; 2) in vivo, Cbl-b−/− mice show a significantly enhanced response to a tumor that is strictly TGF-β regulated; and 3) Cbl-b−/− T effector cells have defective TGF-β-mediated Smad2 phosphorylation. These studies are the first to document that the E3 ubiquitin ligase Cbl-b plays an integral role in T cell TGF-β signaling, and that its absence results in multifunctional TGF-β-related defects that have important disease-related implications.

CD4(+)CD25(+) regulatory T (T reg) cells play a pivotal role in control of the immune response. Transforming growth factor-beta (TGF-beta) has been shown to be required for T reg cell activity; however, precisely how it is involved in the mechanism of suppression is poorly understood. Using the T cell transfer model of colitis, we show here that CD4(+)CD45RB(high) T cells that express a dominant negative TGF-beta receptor type II (dnTbetaRII) and therefore cannot respond to TGF-beta, escape control by T reg cells in vivo. CD4(+)CD25(+) T reg cells from the thymus of dnTbetaRII mice retain the ability to inhibit colitis, suggesting that T cell responsiveness to TGF-beta is not required for the development or peripheral function of thymic-derived T reg cells. In contrast, T reg cell activity among the peripheral dnTbetaRII CD4(+)CD25(+) population is masked by the presence of colitogenic effector cells that cannot be suppressed. Finally, we show that CD4(+)CD25(+) T reg cells develop normally in the absence of TGF-beta1 and retain the ability to suppress colitis in vivo. Importantly, the function of TGF-beta1(-/-) T reg cells was abrogated by anti-TGF-beta monoclonal antibody, indicating that functional TGF-beta can be provided by a non-T reg cell source.

Cancer patients can harbor significant numbers of CD8 and CD4 T cells with specificities to tumor antigens (Ags). Yet, in most cases, such T cells fail to eradicate the tumorin vivo.Here, we investigated the interference of Ag-specific CD4+CD25+regulatory T cells (Treg) with the tumor-specific CD8 T cell immune responsein vivo, by monitoring the homing, expansion, and effector function of both subsets in draining and nondraining lymph nodes. The results show that CD8 cells expand to the same extent and produce similar levels of IFN-γ in the presence or absence of Ag-specific Treg. Nevertheless, these Treg abrogate CD8 T cell-mediated tumor rejection by specifically suppressing the cytotoxicity of expanded CD8 cells. The molecular mechanism of suppression involves TGF-β because expression of a dominant-negative TGF-β receptor by tumor-specific CD8 cells renders them resistant to suppression and is associated with tumor rejection and unimpaired cytotoxicity.

In this study, we show that engagement of CTLA-4 on tumor-infiltrating lymphocytes from low-dose melphalan (l-phenylalanine mustard (l-PAM))-treated MOPC-315 tumor bearers led to IL-10 secretion. In addition, the inhibitory activity of CTLA-4 ligation for IFN-γ secretion following stimulation with anti-CD3 plus anti-CD28 mAb depended on IL-10 production. Consistent with the importance of IL-10 for CTLA-4-mediated inhibition, administration of neutralizing anti-IL-10 mAb to low-dose l-PAM-treated MOPC-315 tumor bearers (administration of blocking anti-CTLA-4 mAb) resulted in enhanced tumor-infiltrating lymphocyte-mediated anti-MOPC-315 cytotoxicity and led to complete tumor eradication in a higher percentage of mice than that observed with low-dose l-PAM alone. The percentage of MOPC-315 tumor-bearing mice cured following administration of neutralizing anti-IL-10 mAb to low-dose l-PAM-treated MOPC-315 tumor bearers was comparable to that observed following administration of blocking anti-CTLA-4 mAb. Moreover, IL-10 neutralization together with CTLA-4 blockade did not provide added therapeutic benefits to low-dose l-PAM-treated MOPC-315 tumor bearers. Taken together, these results indicate that CTLA-4 blockade improves the therapeutic outcome of low-dose l-PAM for MOPC-315 tumor bearers by inhibiting IL-10 secretion as a consequence of blocking CTLA-4 ligation.

Herein we demonstrate that B cell-activating factor of the TNF family (BAFF), a B cell survival factor, also regulates CD21/35 and CD23 expression. BAFF blockade in wild-type mice down-modulates CD21/35 and CD23 on B cells while survival remains intact, and BAFF exposure causes elevated CD21/35 and CD23 expression. Similar down-modulation is observed in bcl-2-transgenic mice treated with a BAFF inhibitor. This is the first evidence that BAFF has a function independent of B cell survival. Reports using CD21/35 and CD23 expression to assess splenic B cell subsets in BAFF-null mice concluded a lack of B cells beyond the immature stage. Since CD21/35 and CD23 are inadequate for delineating B cell subpopulations in BAFF-null mice, we used expression of BAFF-R and several B cell markers to identify more mature splenic B cells in these mice. These data broaden our understanding of BAFF function and correct the view that BAFF-null mice lack mature B cells.

Increasing evidence suggests that atherosclerosis is an inflammatory disease promoted by hypercholesterolemia. The role of adaptive immunity has been controversial, however. We hypothesized that proatherogenic T cells are controlled by immunoregulatory cytokines. Among them, TGF-beta has been implied in atherosclerosis, but its mechanism of action remains unclear. We crossed atherosclerosis-prone ApoE-knockout mice with transgenic mice carrying a dominant negative TGF-beta receptor II in T cells. The ApoE-knockout mice with disrupted TGF-beta signaling in T cells exhibited a sixfold increase in aortic lesion surface area, a threefold increase in aortic root lesion size, and a 125-fold increase in aortic IFN-gamma mRNA when compared with age-matched ApoE-knockout littermates. When comparing size-matched lesions, those of mice with T cell-specific blockade of TGF-beta signaling displayed increased T cells, activated macrophages, and reduced collagen, consistent with a more vulnerable phenotype. Ab's to oxidized LDL, circulating T cell cytokines, and spleen T cell activity were all increased in ApoE-knockout mice with dominant negative TGF-beta receptors in T cells. Taken together, these results show that abrogation of TGF-beta signaling in T cells increases atherosclerosis and suggest that TGF-beta reduces atherosclerosis by dampening T cell activation. Inhibition of T cell activation may therefore represent a strategy for antiatherosclerotic therapy.

The cellular source of B cell activation factor (BAFF) required for peripheral B cell survival/maturation is unknown. To determine the nature of BAFF-producing cells we established and analyzed reciprocal bone marrow (BM) chimeras with wild-type (WT) and BAFF-deficient mice. The results revealed that BAFF production by radiation-resistant stromal cells is completely sufficient to provide a necessary signal for B cell survival/maturation, as BAFF−/− BM cells transferred into lethally irradiated WT mice gave rise to normal numbers of follicular (FO) and marginal zone (MZ) B cell subpopulations. On the other hand, transfer of WT BM into BAFF−/− lethally irradiated mice resulted only in minimal reconstitution of mature FO B cells and no restoration of MZ B cells. Thus, in the absence of BAFF+/+ stromal cells, BAFF production by BM-derived cells, presumably by macrophages, dendritic cells, and/or neutrophils, was not at all sufficient to support normal B cell homeostasis. Interestingly, immunization of both types of chimeras stimulated high levels of antigen-specific antibody secretion, indicating that either stromal cell– or hematopoietic cell–derived BAFF is sufficient for B cell antibody responses.

Pancreatic lymph node-derived CD4 + CD25 + T regulatory (Treg) cells inhibit in situ differentiation of islet-reactive CD8 + T cells into cytotoxic T lymphocytes, thereby preventing diabetes progression. The mechanism by which these Treg cells suppress anti-islet CD8 + T cells is unknown. Here, we show by using a CD8 + T cell-mediated model of type 1 diabetes that transforming growth factor (TGF)-β–TGF-β receptor signals are critical for CD4 + CD25 + Treg cell regulation of autoreactive islet-specific cytotoxic T lymphocytes. Transgenic expression of tumor necrosis factor α from birth to 25 days of age in the islets of B6 mice that constitutively express CD80 on their β cells results in accumulation of CD4 + CD25 + TGF-β + cells exclusively in the islets and pancreatic lymph nodes, which delays diabetes progression. In contrast, expression of tumor necrosis factor α until 28 days of age prevents islet accumulation of CD4 + CD25 + TGF-β + Treg cells, resulting in acceleration to diabetes. Furthermore, adoptive transfer experiments demonstrated that CD4 + CD25 + Treg cells could not control naïve or activated isletreactive CD8 + T cells bearing a dominant negative TGF-β receptor type II. Our data demonstrate that, in vivo , TGF-β signaling in CD8 + T cells is critical for CD4 + CD25 + Treg cell suppression of isletreactive CD8 + T cells in type 1 diabetes.

BAFF is considered a therapeutic target because dysregulated production of BAFF can induce systemic lupus erythematosus-like phenotype in mice, and elevated levels of BAFF are associated with disease severity in systemic lupus erythematosus and rheumatoid arthritis patients. Fc fusion decoy receptors, BCMA-Fc and BAFF-R-Fc, are therapeutic candidates for blocking BAFF. While studying their interactions with BAFF, we found that BAFF-R-Fc is more effective than BCMA-Fc for blocking BAFF binding to its receptors. We also found that a trimeric BAFF can bind more than one BAFF-R-Fc but only one BCMA-Fc. Moreover, we show that, in contrast to monovalent BAFF-R-Fc, monovalent BCMA does not form stable complexes with BAFF. Differences in their interaction with BAFF predict BAFF-R-Fc would be a better inhibitor. Indeed, we show BAFF-R-Fc is 10-fold more efficacious than BCMA-Fc for blocking BAFF-induced B cell proliferation in vitro and for blocking BAFF-mediated survival of mouse splenic B lymphocytes in vivo.

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease triggered by infection with the human gliotropic JC virus (JCV). Due to the human-selective nature of the virus, there are no animal models available to investigate JCV pathogenesis. To address this issue, we developed mice with humanized white matter by engrafting human glial progenitor cells (GPCs) into neonatal immunodeficient and myelin-deficient mice. Intracerebral delivery of JCV resulted in infection and subsequent demyelination of these chimeric mice. Human GPCs and astrocytes were infected more readily than oligodendrocytes, and viral replication was noted primarily in human astrocytes and GPCs rather than oligodendrocytes, which instead expressed early viral T antigens and exhibited apoptotic death. Engraftment of human GPCs in normally myelinated and immunodeficient mice resulted in humanized white matter that was chimeric for human astrocytes and GPCs. JCV effectively propagated in these mice, which indicates that astroglial infection is sufficient for JCV spread. Sequencing revealed progressive mutation of the JCV capsid protein VP1 after infection, suggesting that PML may evolve with active infection. These results indicate that the principal CNS targets for JCV infection are astrocytes and GPCs and that infection is associated with progressive mutation, while demyelination is a secondary occurrence, following T antigen-triggered oligodendroglial apoptosis. More broadly, this study provides a model by which to further assess the biology and treatment of human-specific gliotropic viruses.

Despite the existence of tumor-specific antigens and demonstrated presence of tumor-specific immune cells, the majority of tumors manage to avoid immune-mediated destruction. Various mechanisms have been suggested for tumor evasion from immune response. One such mechanism is thought to be mediated by transforming growth factor-beta (TGF-beta), an immunosuppressive cytokine found at the site of most tumors. We demonstrate here that T-cell-specific blockade of TGF-beta signaling allows the generation of an immune response capable of eradicating tumors in mice challenged with live tumor cells. In addition, we provide mechanisms through which abrogation of TGF-beta signaling leads to the enhancement of anti-tumor immunity. Our data indicate that T-cell-specific blockade of TGF-beta signaling has strong therapeutic potential to shift the balance of the immune response in favor of anti-tumor immunity.

We have previously demonstrated the importance of endogenous GM-CSF production for the B7-2-dependent potentiating effect of exogenous TNF for CTL generation by stimulation cultures of splenic cells from mice bearing a large MOPC-315 tumor. Here we show that addition of GM-CSF to stimulation cultures of such tumor-bearer splenic cells also leads to the generation of enhanced anti-MOPC-315 CTL activity via a B7-dependent mechanism. However, while the potentiating effect of TNF was previously shown to be IL-2-independent, the potentiating effect of GM-CSF is shown here to be completely IL-2-dependent. Still, the potentiating activity of exogenous GM-CSF for the in vitro generation of CTL activity is shown to depend completely on endogenous TNF production. Finally, TNF and GM-CSF may cooperate in enhancing the in vivo generation of CTL activity in MOPC-315 tumor bearers because low-dose melphalan ( l -phenylalanine mustard) therapy, which was previously shown to lead to the rapid up-regulation of TNF production at the tumor site and the subsequent TNF-dependent in vivo acquisition of potent CTL activity, is shown here to lead to the rapid up-regulation of GM-CSF production at the tumor site.

We have shown previously that inhalation of cowshed dust extract (CDE) resulted in decreased airway reactivity, eosinophilic inflammation and sensitization in a mouse model of allergic asthma. Our data suggested down-regulation of allergic immune response rather than activation of a Th1 response towards the model allergen. However, the precise mechanism of allergy protection is not yet understood in detail. To gain deeper insight into CDE-induced immune modulation, we have analysed the effects of CDE on dendritic cell biology. Dendritic cells were generated from murine bone marrow cells (BMDC). Cells were stimulated with CDE and subsequently used to sensitize mice via the airways. Our results showed that cells were not able to prime mice for allergic immune response when they were treated with CDE 2 days before pulsing with allergen, whereas cells that were stimulated with CDE simultaneously to OVA pulsing induced a fully developed allergic immune response. Surprisingly, CDE-treated cells that were not able to prime mice for allergic immune response exhibit an activated phenotype with high expression of the co-stimulatory surface molecule CD86. Moreover, CDE-treated cells transiently produced high amounts of cytokines such as IL-10, IL-12p70 and TNF-α. Interestingly, blocking of autocrine-produced IL-10 in vitro partially restored the allergy-inducing capacity of CDE-exposed cells. Thus, we conclude that prolonged exposure to CDE reduces the allergy-inducing capacity of dendritic cells. Furthermore, we present evidence that an autocrine IL-10 dependent mechanism seems to be involved in down-regulation of dendritic cell function due to stimulation with CDE.

Absence of transforming growth factor-beta (TGF-beta) signaling to T cells in mice results in an increase in T cell numbers, an activated CD44 high, CD69-, CD25- T cell phenotype and a T cell-mediated injury to many organs. It is not known if such T cell activation in the absence of TGF-beta signaling is spontaneous or due to aberrant T cell responses to a physiological stimulus. We used adoptive transfer of CD8+ T cells from mice double transgenic for the OT-1 TCR and the TGF-beta1-dominant negative transgene [OT-dominant-negative receptor (DNR)] to investigate the role of TGF-beta in regulating CD8+ T cell activation in vivo. The activation and expansion of single-transgenic OT and double-transgenic OT-DNR cells to oral antigens, high-affinity and low-affinity peptides were indistinguishable. Activation with high-affinity peptide and CFA however resulted in greater expansion of OT-DNR cells in comparison to OT cells. Low-affinity peptide and adjuvant did not result in OT cell activation or expansion but results in up-regulation of CD44 on OT-DNR cells. These data show that TGF-beta functions in vivo to limit the scale of CD8+ T cell expansion after high-affinity peptide-MHC interactions. TGF-beta also limits T cell activation to the highest affinity peptide-MHC interactions. The increase in T cell number and activation present in TGF-beta-deficient and TGF-beta DNR-expressing mice may be due to the loss of these two phenomena.

B cell activating factor of the tumor necrosis factor (TNF) family (BAFF) and a proliferation-inducing ligand (APRIL) are closely related ligands within the TNF superfamily that play important roles in B lymphocyte biology. Both ligands share two receptors—transmembrane activator and calcium signal–modulating cyclophilin ligand interactor (TACI) and B cell maturation antigen (BCMA)—that are predominantly expressed on B cells. In addition, BAFF specifically binds BAFF receptor, whereas the nature of a postulated APRIL-specific receptor remains elusive. We show that the TNF homology domain of APRIL binds BCMA and TACI, whereas a basic amino acid sequence (QKQKKQ) close to the NH2 terminus of the mature protein is required for binding to the APRIL-specific “receptor.” This interactor was identified as negatively charged sulfated glycosaminoglycan side chains of proteoglycans. Although T cell lines bound little APRIL, the ectopic expression of glycosaminoglycan-rich syndecans or glypicans conferred on these cells a high binding capacity that was completely dependent on APRIL's basic sequence. Moreover, syndecan-1–positive plasma cells and proteoglycan-rich nonhematopoietic cells displayed high specific, heparin-sensitive binding to APRIL. Inhibition of BAFF and APRIL, but not BAFF alone, prevented the survival and/or the migration of newly formed plasma cells to the bone marrow. In addition, costimulation of B cell proliferation by APRIL was only effective upon APRIL oligomerization. Therefore, we propose a model whereby APRIL binding to the extracellular matrix or to proteoglycan-positive cells induces APRIL oligomerization, which is the prerequisite for the triggering of TACI- and/or BCMA-mediated activation, migration, or survival signals.

Interferon-gamma and interleukin 12 produced by the innate arm of the immune system are important regulators of T helper type 1 (T(H)1) cell development, but signals that negatively regulate their expression remain controversial. Here we show that transforming growth factor-beta (TGF-beta) controlled T(H)1 differentiation through the regulation of interferon-gamma produced by natural killer (NK) cells. Blockade of TGF-beta signaling in NK cells caused the accumulation of a large pool of NK cells secreting copious interferon-gamma, responsible for T(H)1 differentiation and protection from leishmania infection. In contrast, blockade of TGF-beta signaling in dendritic cells did not affect dendritic cell homeostasis or interleukin 12 production, thus indicating a previously undescribed demarcation of the function of TGF-beta in NK cells versus dendritic cells.

Regulation by transforming growth factor (TGF)-beta plays an important role in immune homeostasis. TGF-beta inhibits T cell functions by blocking both proliferation and differentiation. Here we show that TGF-beta blocks Th1 differentiation by inhibiting the expression of T-bet, the apparent masterregulator of T helper (Th)1 differentiation. Restoration of T-bet expression through retroviral transduction of T-bet into developing Th1 cells abrogated the inhibitory effect of TGF-beta. In addition, we show that, contrary to prior suggestions, downregulation of interleukin 12 receptor beta2 chain is not key to the TGF-beta-mediated effect. Furthermore, we show that the direct inhibitory effect of TGF-beta on T cells is responsible, at least in part, for the inability of BALB/c mice to mount a Leishmania-specific Th1 response and to clear Leishmanial infection.

TGF-β is an important immunomodulatory cytokine that can inhibit differentiation of effector T cells. In this report, we address the molecular mechanisms through which TGF-β inhibits differentiation of CD4+ cells into Th type 2 cells. We demonstrate that TGF-β inhibits GATA-3 expression in developing Th cells. We also show that inhibition of GATA-3 expression by TGF-β is a major mechanism of inhibition of Th2 differentiation by TGF-β as ectopic expression of GATA-3 in developing T cells overcomes the ability of TGF-β to inhibit Th2 differentiation. TGF-β likely inhibits GATA-3 expression at the transcriptional level and does so without interfering with IL-4 signaling.

Atherosclerosis is a systemic disease of the large arteries, and activation of inflammatory pathways is important in its pathogenesis1. Increasing evidence supports the importance of CD40–CD154 interactions in atherosclerosis2,3, interactions originally known to be essential in major immune reactions4 and autoimmune diseases5. CD40 is present on atheroma-derived cells in vitro and in human atheromata in situ6. Ligation of CD40 on atheroma-associated cells in vitro activates the production of chemokines6, cytokines6, matrix metalloproteinases7,8, adhesion molecules9,10 and tissue factor7, substances responsible for lesion progression and plaque destabilization1. Administration of antibody against CD154 to low-density lipoprotein receptor-deficient mice has been shown to reduce atherosclerosis and decrease T-lymphocyte and macrophage content; however, only initial lesions were studied3. Here, we determined the effect of genetic disruption of CD154 in ApoE–/– mice in both initial and advanced atherosclerotic lesions. Plaque area was reduced 550%. In contrast to previous reports, initial lesion development was not affected. Advanced plaques in CD154–/–ApoE–/– mice had a less-lipid-containing, collagen-rich, stable plaque phenotype, with a reduced T-lymphocyte/macrophage content. These data indicate that CD40–CD154 signaling is important in late atherosclerotic changes, such as lipid core formation and plaque destabilization.

We have previously shown the importance of endogenous tumor necrosis factor (TNF) production for the curative effectiveness of low-dose melphalan (L-phenylalanine mustard) for mice bearing a large MOPC-315 tumor. In the current study we demonstrate that low-dose melphalan is actually associated with enhanced expression of mRNA for TNF alpha in the s.c. tumor nodule. Moreover, the expression of mRNA for interferon gamma (IFN gamma) and interleukin-12 (IL-12; p40) is also elevated at the tumor site. However, while elevation in the expression of mRNA for TNF alpha and IFN gamma is evident within 24 h after the chemotherapy, elevation in the expression of mRNA for IL-12(p40) is first evident 72 h after the chemotherapy. Moreover, neutralizing anti-IFN gamma mAb, like neutralizing anti-TNF mAb but not neutralizing anti-IL-12 mAb, reduced the curative effectiveness of low-dose melphalan for MOPC-315 tumor bearers. Studies into the mechanism through which IFN gamma mediates its antitumor effect in low-dose-melphalan-treated MOPC-315 tumor-bearing mice revealed that MOPC-315 tumor cells, which are not sensitive to the direct antitumor effects of TNF, display some sensitivity to the antiproliferative activity of high concentrations of IFN gamma. However, unlike TNF alpha, IFN gamma is unable to promote the generation of anti-MOPC-315 cytotoxic T lymphocyte activity and, in fact, exerts an inhibitory activity on CTL generation. Taken together, our studies illustrate that low-dose melphalan therapy of MOPC-315 tumor bearers is associated with the rapid elevation in the expression of mRNA for IFN gamma and TNF, two cytokines which are important for the curative effectiveness of low-dose melphalan, and which mediate their antitumor effect, in part, through distinct mechanisms.

The current studies demonstrate that MOPC-315 tumor cells secrete large amounts of interleukin-10 (IL-10), which contributes to the inhibitory activity of MOPC-315 culture supernatants for the in vitro generation of antitumor cytotoxicity by MOPC-315-"immune" spleen cells. Moreover, addition of neutralizing monoclonal anti-IL-10 antibody to the in vitro stimulation cultures of cells from the tumor infiltrated spleens of mice bearing a large MOPC-315 tumor resulted in the generation of enhanced anti-MOPC-315 cytotoxicity. In contrast, addition of monoclonal anti-IL-10 antibody to the in vitro stimulation cultures of splenic cells from mice that are in the final stages of immune-mediated tumor eradication as a consequence of low-dose melphalan (L-phenylalanine mustard; L-PAM) therapy (and whose spleens no longer contain metastatic tumor cells) did not lead to enhancement in the in vitro generation of antitumor cytotoxicity. The cessation of IL-10 secretion as a consequence of low-dose L-PAM therapy of MOPC-315 tumor bearers was found to be accompanied by the acquisition of the ability to secrete interferon gamma (IFN gamma) by the splenic cells. In addition, by day 2 after low-dose L-PAM therapy a drastic decrease in the amount of IL-10 secreted by the s.c. tumor nodules was noted, which preceded the accumulation of tumor-infiltrating lymphocytes capable of secreting IFN gamma. Thus, low-dose L-PAM therapy of mice bearing a large MOPC-315 tumor leads to a shift in cytokine production from a Th2-type cytokine to a Th1-type cytokine, and it is conceivable that this shift in cytokine production plays an important role in the low-dose L-PAM-induced acquisition of antitumor immunity by hitherto immunosuppressed mice bearing a large MOPC-315 tumor.

Background Atopic dermatitis and allergic contact dermatitis are skin disorders triggered by epicutaneous sensitization with protein antigens and contact sensitization with haptens, respectively. Skin is colonized with bacteria, which are a source of Toll-like receptor (TLR) 2 ligands. Objective We sought to examine the role of TLR2 in murine models of atopic dermatitis and allergic contact dermatitis. Methods TLR2 −/− mice and wild-type littermates were epicutaneously sensitized with ovalbumin (OVA) or contact sensitized with oxazolone (OX). Skin histology was assessed by means of hematoxylin and eosin staining and immunohistochemistry. Ear swelling was measured with a micrometer. Cytokine mRNA expression was examined by means of quantitative RT-PCR. Antibody levels and splenocyte secretion of cytokines in response to OVA stimulation were measured by means of ELISA. Dendritic cells were examined for their ability to polarize T-cell receptor/OVA transgenic naive T cells to T H 1 and T H 2. Results In response to OVA sensitization, TLR2 −/− mice experienced skin infiltration with eosinophils and CD4 + cells, as well as upregulation of T H 2 cytokine mRNAs that was comparable with that seen in wild-type littermates. In contrast, epidermal thickening, IFN-γ expression in the skin, IFN-γ production by splenocytes, and IgG2a anti-OVA antibody levels were impaired in TLR2 −/− mice. After OX ear challenge, contact sensitized TLR2 −/− mice exhibited defective ear swelling with impaired cellular infiltration, decreased epidermal thickening and local IFN-γ expression, and impaired OX-specific IgG2a responses. Dendritic cells from TLR2 −/− mice induced significantly lower production of IFN-γ but normal IL-4 and IL-13 production in naive T cells. Conclusions These results indicate that TLR2 promotes the IFN-γ response to cutaneously introduced antigens.

Targeted mutation of TGFbeta1 in mice demonstrated that TGFbeta1 is one of the key negative regulators of immune homeostasis, as its absence leads to activation of a self-targeted immune response. Nevertheless, because of the highly pleiotropic properties of TGFbeta and the presence of TGFbeta receptors on most cell types, its biologic role in the regulation of immune homeostasis is not yet understood. To limit the consequences of TGFbeta effects to a single cell type, we developed a transgenic approach to abrogate the TGFbeta response in key immune cells. Specifically, we expressed a dominant-negative TGFbeta receptor type II under a T cell-specific promoter and created a mouse model where signaling by TGFbeta is blocked specifically in T cells. Using this transgenic model, we show that T cell homeostasis requires TGFbeta signaling in T cells.