Defective TCR expression in transgenic mice constructed using cDNA-based alpha- and beta-chain genes under the control of heterologous regulatory elements

Role of CXCR5 and CCR7 in follicular Th cell positioning and appearance of a programmed cell death gene-1high germinal center-associated subpopulation

Th cell access to primary B cell follicles is dependent on CXCR5. However, whether CXCR5 induction on T cells is sufficient in determining their follicular positioning has been unclear. In this study, we find that transgenic CXCR5 overexpression is not sufficient to promote follicular entry of naive T cells unless the counterbalancing influence of CCR7 ligands is removed. In contrast, the positioning of Ag-engaged T cells at the B/T boundary could occur in the absence of CXCR5. The germinal center (GC) response was 2-fold reduced when T cells lacked CXCR5, although these T cells were able to access the GC. Finally, CXCR5(high)CCR7(low) T cells were found to have elevated IL-4 transcript and programmed cell death gene-1 (PD-1) expression, and PD-1(high) cells were reduced in the absence of T cell CXCR5 or in mice compromised in GC formation. Overall, these findings provide further understanding of how the changes in CXCR5 and CCR7 expression regulate Th cell positioning during Ab responses, and they suggest that development and/or maintenance of a PD-1(high) follicular Th cell subset is dependent on appropriate interaction with GC B cells.

CD8+ CTL priming by exact peptide epitopes in incomplete Freund's adjuvant induces a vanishing CTL response, whereas long peptides induce sustained CTL reactivity

Therapeutic vaccination trials, in which patients with cancer were vaccinated with minimal CTL peptide in oil-in-water formulations, have met with limited success. Many of these studies were based on the promising data of mice studies, showing that vaccination with a short synthetic peptide in IFA results in protective CD8(+) T cell immunity. By use of the highly immunogenic OVA CTL peptide in IFA as a model peptide-based vaccine, we investigated why minimal CTL peptide vaccines in IFA performed so inadequately to allow full optimization of peptide vaccination. Injection of the minimal MHC class I-binding OVA(257-264) peptide in IFA transiently activated CD8(+) effector T cells, which eventually failed to undergo secondary expansion or to kill target cells, as a result of a sustained and systemic presentation of the CTL peptides gradually leaking out of the IFA depot without systemic danger signals. Complementation of this vaccine with the MHC class II-binding Th peptide (OVA(323-339)) restored both secondary expansion and in vivo effector functions of CD8(+) T cells. Simply extending the CTL peptide to a length of 30 aa also preserved these CD8(+) T cell functions, independent of T cell help, because the longer CTL peptide was predominantly presented in the locally inflamed draining lymph node. Importantly, these functional differences were reproduced in two additional model Ag systems. Our data clearly show why priming of CTL with minimal peptide epitopes in IFA is suboptimal, and demonstrate that the use of longer versions of these CTL peptide epitopes ensures the induction of sustained effector CD8(+) T cell reactivity in vivo.

BCL11B is required for positive selection and survival of double-positive thymocytes

Transcriptional control of gene expression in double-positive (DP) thymocytes remains poorly understood. We show that the transcription factor BCL11B plays a critical role in DP thymocytes by controlling positive selection of both CD4 and CD8 lineages. BCL11B-deficient DP thymocytes rearrange T cell receptor (TCR) alpha; however, they display impaired proximal TCR signaling and attenuated extracellular signal-regulated kinase phosphorylation and calcium flux, which are all required for initiation of positive selection. Further, provision of transgenic TCRs did not improve positive selection of BCL11B-deficient DP thymocytes. BCL11B-deficient DP thymocytes have altered expression of genes with a role in positive selection, TCR signaling, and other signaling pathways intersecting the TCR, which may account for the defect. BCL11B-deficient DP thymocytes also presented increased susceptibility to spontaneous apoptosis associated with high levels of cleaved caspase-3 and an altered balance of proapoptotic/prosurvival factors. This latter susceptibility was manifested even in the absence of TCR signaling and was only partially rescued by provision of the BCL2 transgene, indicating that control of DP thymocyte survival by BCL11B is nonredundant and, at least in part, independent of BCL2 prosurvival factors.

Indirect involvement of allergen-captured mast cells in antigen presentation

It is generally thought that mast cells influence T-cell activation nonspecifically through the release of inflammatory mediators. In this report, we provide evidence that mast cells may also affect antigen-specific T-cell responses by internalizing immunoglobulin E-bound antigens for presentation to antigen-specific T cells. Surprisingly, T-cell activation did not require that mast cells express major histocompatibility complex class II, indicating that mast cells were not involved in the direct presentation of the internalized antigens. Rather, the antigen captured by mast cells is presented by other major histocompatibility complex class II(+) antigen-presenting cells. To explore how this may occur, we investigated the fate of mast cells stimulated by antigen and found that FcepsilonRI crosslinking enhances mast cell apoptosis. Cell death by antigen-captured mast cells was required for efficient presentation because protection of mast cell death significantly decreased T-cell activation. These results suggest that mast cells may be involved in antigen presentation by acting as an antigen reservoir after antigen capture through specific immunoglobulin E molecules bound to their FcepsilonRI. This mechanism may contribute to how mast cells impact the development of T-cell responses.

In vivo transformation of mouse conventional CD8alpha+ dendritic cells leads to progressive multisystem histiocytosis

Division and proliferation of dendritic cells (DCs) have been proposed to contribute to homeostasis and to prolonged antigen presentation. Whether abnormal proliferation of dendritic cells causes Langerhans cell histiocytosis (LCH) is a highly debated topic. Transgenic expression of simian virus 40 (SV40) T antigens in mature DCs allowed their transformation in vivo while maintaining their phenotype, function, and maturation capacity. The transformed cells were differentiated splenic CD8 alpha-positive conventional dendritic cells with increased Langerin expression. Their selective transformation was correlated with higher steady-state cycling compared with CD8 alpha-negative DCs in wild-type and transgenic mice. Mice developed a DC disease involving the spleen, liver, bone marrow, thymus, and mesenteric lymph node. Surprisingly, lesions displayed key immunohistologic features of Langerhans cell histiocytosis, including expression of Langerin and absence of the abnormal mitoses observed in Langerhans cell sarcomas. Our results demonstrate that a transgenic mouse model with striking similarities to aggressive forms of multisystem histiocytosis, such as the Letterer-Siwe syndrome, can be obtained by transformation of conventional DCs. These findings suggest that conventional DCs may cause some human multisystem LCH. They can reveal shared molecular pathways for human histiocytosis between humans and mice.

Steady-state dendritic cells expressing cognate antigen terminate memory CD8+ T-cell responses

Antigen stimulation of naive T cells in conjunction with strong costimulatory signals elicits the generation of effector and memory populations. Such terminal differentiation transforms naive T cells capable of differentiating along several terminal pathways in response to pertinent environmental cues into cells that have lost developmental plasticity and exhibit heightened responsiveness. Because these cells exhibit little or no need for the strong costimulatory signals required for full activation of naive T cells, it is generally considered memory and effector T cells are released from the capacity to be inactivated. Here, we show that steady-state dendritic cells constitutively presenting an endogenously expressed antigen inactivate fully differentiated memory and effector CD8(+) T cells in vivo through deletion and inactivation. These findings indicate that fully differentiated effector and memory T cells exhibit a previously unappreciated level of plasticity and provide insight into how memory and effector T-cell populations may be regulated.

Lymphotoxin pathway and Aire influences on thymic medullary epithelial cells are unconnected

The lymphotoxin pathway is critical for the development and maintenance of peripheral lymphoid organs. Mice with deficiencies in members of this pathway lack lymph nodes and Peyer's patches and have abnormal spleen architecture. These animals also develop autoantibodies to and lymphocytic infiltrates of multiple organs, provoking speculation that the lymphotoxin pathway may play a role in central tolerance induction. Indeed, a series of reports has claimed that lymphotoxin signals control the expression of Aire, a transcriptional regulator that is expressed in medullary epithelial cells of the thymus, mediates ectopic transcription of genes encoding a variety of peripheral tissue Ags, and promotes clonal deletion of self-reactive thymocytes. However, one report argued that lymphotoxin signals regulate the composition and organization of the thymus, particularly of the medullary epithelial compartment. Herein, we resolve this controversy in favor of the latter view. The expression and function of Aire were unaffected in medullary epithelial cells of mice lacking either lymphotoxin beta receptor or the lymphotoxin alpha-chain, and there was minimal overlap between the sets of genes controlled by Aire and lymphotoxin. Instead, both knockout lines showed abnormal medullary epithelial cell organization, and the line lacking the beta receptor had significantly fewer medullary epithelial cells. In short, the lymphotoxin pathway drives the developmental rather than selectional properties of thymic stromal cells.

Increasing the survival of dendritic cells in vivo does not replace the requirement for CD4+ T cell help during primary CD8+ T cell responses

The survival of dendritic cells (DC) in vivo determines the duration of Ag presentation and is critical in determining the strength and magnitude of the resulting T cell response. We used a mouse model to show that Ag-loaded C57BL/6 DC (MHC class II(+/+) (MHC II(+/+))) that reach the lymph node survived longer than Ag-loaded MHC II(-/-) DC, with the numbers of C57BL/6 DC being approximately 2.5-fold the number of the MHC II(-/-) DC by day 4 and approximately 5-fold by day 7. The differential survival of DC in vivo was not affected by low doses of LPS, but in vitro pretreatment with CD40L or with high doses of LPS increased the numbers of MHC II(-/-) DC to levels approaching those of C57BL/6 DC. Regardless of their numbers and relative survival in lymph nodes, MHC II(-/-) DC were profoundly defective in their ability to induce CTL responses against the gp33 peptide epitope, and were unable to induce expansion and optimal cytotoxic activity of CD8(+) T cells specific for the male Ag UTY. We conclude that CD4(+) T cell help for CD8(+) responses involves mechanisms other than the increased survival of Ag-presenting DC in the lymph node.

Dendritic cell preactivation impairs MHC class II presentation of vaccines and endogenous viral antigens

When dendritic cells (DCs) encounter signals associated with infection or inflammation, they become activated and undergo maturation. Mature DCs are very efficient at presenting antigens captured in association with their activating signal but fail to present subsequently encountered antigens, at least in vitro. Such impairment of MHC class II (MHC II) antigen presentation has generally been thought to be a consequence of down-regulation of endocytosis, so it might be expected that antigens synthesized by the DCs themselves (for instance, viral antigens) would still be presented by mature DCs. Here, we show that DCs matured in vivo could still capture and process soluble antigens, but were unable to present peptides derived from these antigens. Furthermore, presentation of viral antigens synthesized by the DCs themselves was also severely impaired. Indeed, i.v. injection of pathogen mimics, which caused systemic DC activation in vivo, impaired the induction of CD4 T cell responses against subsequently encountered protein antigens. This immunosuppressed state could be reversed by adoptive transfer of DCs loaded exogenously with antigens, demonstrating that impairment of CD4 T cell responses was due to lack of antigen presentation rather than to overt suppression of T cell activation. The biochemical mechanism underlying this phenomenon was the down-regulation of MHC II-peptide complex formation that accompanied DC maturation. These observations have important implications for the design of prophylactic and therapeutic DC vaccines and contribute to the understanding of the mechanisms causing immunosuppression during systemic blood infections.

Human Flt-3-ligand-mobilized dendritic cells require additional activation to drive effective immune responses

OBJECTIVE

Dendritic cells (DCs) play a pivotal role in the induction of immunity in response to pathogenic challenge or vaccination. As such, the fms-like tyrosine kinase 3-ligand (Flt-3L) has been used to increase DC populations in vivo, with contrasting outcomes, which include an increase in immunity, tolerance induction, or expansion of regulatory cells. This study examines the adjuvant role that human Flt-3L (hFL) administration has in generating immune responses upon immunization with a poorly immunogenic and soluble protein antigen.

MATERIALS AND METHODS

Mice were immunized with the nominal antigen, ovalbumin, alone or with antigen emulsified in complete Freund's adjuvant (CFA), with or without prior hFL-mediated expansion of DC subsets. The maturation of DC subsets and activation status of antigen-specific T cells were analyzed by flow cytometry, with effector function assessed in cytolytic T-lymphocyte assays.

RESULTS

hFL treatment expanded both conventional DC and plasmacytoid DC in vivo, resulting in increased antigen presentation by both direct and cross-presentation pathways. However, it was only in the context of CFA that antigen immunization could mature DCs and subsequently fully activate antigen-specific T cells with enhanced cytolytic activity.

CONCLUSIONS

Our studies reveal that hFL essentially acts as a coadjuvant, as hFL augments the size of an immune response but requires further adjuvant activation to alter the quality of the response.

TCR affinity promotes CD8+ T cell expansion by regulating survival

Ligation with high affinity ligands are known to induce T lymphocytes to become fully activated effector cells while ligation with low affinity ligands (or partial agonists) may result in a delayed or incomplete response. We have examined the quantitative features of CD8(+) T cell proliferation induced by peptides of different TCR affinities at a range of concentrations in the mouse OT-I model. Both the frequency of cells responding and the average time taken for cells to reach their first division are affected by peptide concentration and affinity. Consecutive division times, however, remained largely unaffected by these variables. Importantly, we identified affinity to be the sole regulator of cell death in subsequent division. These results suggest a mechanism whereby TCR affinity detection can modulate the subsequent rate of T cell growth and ensure the dominance of higher affinity clones over time.

Differential Requirements for OX40 Signals on Generation of Effector and Central Memory CD4+ T Cells

Memory T cells can be divided into effector memory (T(EM)) and central memory (T(CM)) subsets based on their effector function and homing characteristics. Although previous studies have demonstrated that TCR and cytokine signals mediate the generation of the two memory subsets of CD8(+) T cells, the mechanisms for generation of the CD4(+) T(EM) and T(CM) cell subsets are unknown. We found that OX40-deficient mice showed a marked reduction in the number of CD4(+) T(EM) cells, whereas the number of CD4(+) T(CM) cells was normal. Adoptive transfer experiments using Ag-specific CD4(+) T cells revealed that OX40 signals during the priming phase were indispensable for the optimal generation of the CD4(+) T(EM), but not the CD4(+) T(CM) population. In a different transfer experiment with in vitro established CD4(+)CD44(high)CD62L(low) (T(EM) precursor) and CD4(+)CD44(high)CD62L(high) (T(CM) precursor) subpopulations, OX40-KO T(EM) precursor cells could not survive in the recipient mice, whereas wild-type T(EM) precursor cells differentiated into both T(EM) and T(CM) cells. In contrast, T(CM) precursor cells mainly produced T(CM) cells regardless of OX40 signals, implying the dispensability of OX40 for generation of T(CM) cells. Nevertheless, survival of OX40-KO T(EM) cells was partially rescued in lymphopenic mice. During in vitro recall responses, the OX40-KO T(EM) cells that were generated in lymphopenic recipient mice showed impaired cytokine production, suggesting an essential role for OX40 not only on generation but also on effector function of CD4(+) T(EM) cells. Collectively, the present results indicate differential requirements for OX40 signals on generation of CD4(+) T(EM) and T(CM) cells.

Differential priming of CD8 and CD4 T-cells in animal models of autoimmune hepatitis and cholangitis

The pathogenesis of autoimmune liver diseases is poorly understood. Animal models are necessary to investigate antigen presentation and priming of T-cells in the context of autoimmunity in the liver. Transgenic mouse models were generated in which the model antigen ovalbumin is expressed in hepatocytes (TF-OVA) or cholangiocytes (ASBT-OVA). Transgenic OT-I (CD8) or OT-II (CD4) T-cells specific for ovalbumin were adoptively transferred into TF-OVA and ASBT-OVA mice to induce in vivo priming of antigen-specific T-cells. T-cell migration and activation, as well as induction of liver inflammation, were studied. OT-I T-cells preferentially located to the liver of both mouse strains whereas no migration of OT-II T-cells to the liver was observed. OT-I T-cells proliferated in the liver of TF-OVA mice and the liver and liver draining lymph nodes of ASBT-OVA mice. OT-II CD4 T-cells were activated in spleen and liver draining lymph node of TF-OVA mice but not in ASBT-OVA mice. Transfer of OT-I T-cells led to histologically distinct inflammatory conditions in the liver of ASBT-OVA and TF-OVA mice and caused liver injury as determined by the elevation of serum alanine aminotransferase.

CONCLUSION

An antigen expressed in hepatocytes is presented to CD8 and CD4 T-cells, whereas the same antigen expressed in cholangiocytes is presented to CD8 but not CD4 T-cells. In both models, activation of CD8 T-cells occurs within the liver and causes liver inflammation. The models presented here are valuable to investigate the priming of T-cells in the liver and their role in the development of autoimmune disease of the liver.

Allopeptide-specific CD4(+) T cells facilitate the differentiation of directly alloreactive graft-infiltrating CD8(+) T Cells

To investigate the mechanism of CD4(+) T-cell help during the activation and differentiation of directly alloreactive CD8(+) T cells, we examined the development of obliterative airways disease (OAD) following transplantation of airways into fully mismatched recipient mice deficient in CD4(+) T cells. BALB/c trachea allografts became fibrosed significantly less frequently in B6 CD4(-/-) recipients as compared to wildtype controls. Furthermore, class I-directed cytotoxicity failed to develop in the absence of CD4(+) T cells. The infiltration of graft tissue by primed L(d)-specific directly alloreactive 2C CD8(+) T cells was not found to depend on the presence of CD4(+) T cells. Nevertheless, graft-infiltrating 2C CD8(+) T cells failed to express CD69 and granzyme B when CD4(+) T-cell help was unavailable. Importantly, reconstitution of B6 CD4(-/-) recipient mice with graft peptide-specific TCR-Tg CD4(+) T cells (OT-II or TEa) capable of recognizing antigen only on recipient APC allowed for full expression of CD69 and granzyme B by the directly alloreactive CD8(+) T cells and restored the capacity of recipients to reject their allografts. These results demonstrate that indirectly alloreactive CD4(+) T cells ensure the optimal activation and differentiation of graft-infiltrating directly alloreactive CD8(+) T cells independent of donor APC recognition.

Resistance to experimental autoimmune encephalomyelitis and impaired T cell priming by dendritic cells in Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 mutant mice

Src homology 2 domain-containing protein tyrosine phosphatase (SHP) substrate-1 (SHPS-1) is a transmembrane protein that binds the protein tyrosine phosphatases SHP-1 and SHP-2 through its cytoplasmic region and is expressed on the surface of CD11c(+) dendritic cells (DCs) and macrophages. In this study, we show that mice that express a mutant form of SHPS-1 lacking most of the cytoplasmic region are resistant to experimental autoimmune encephalomyelitis (EAE) in response to immunization with a peptide derived from myelin oligodendrocyte glycoprotein (MOG (35-55)). The MOG (35-55)-induced proliferation of, and production of IFN-gamma, IL-2, and IL-17, by T cells from immunized SHPS-1 mutant mice were reduced compared with those apparent for wild-type cells. The abilities of splenic DCs from mutant mice to stimulate an allogenic MLR and to prime Ag-specific T cells were reduced. Both IL-12-stimulated and TLR-dependent cytokine production by DCs of mutant mice were also impaired. Finally, SHPS-1 mutant mice were resistant to induction of EAE by adoptive transfer of MOG (35-55)-specific T cells. These results show that SHPS-1 on DCs is essential for priming of naive T cells and the development of EAE. SHPS-1 is thus a potential therapeutic target in inflammatory disorders of the CNS and other autoimmune diseases.

Antigen presentation and transfer between B cells and macrophages

B cells play an active role in directing immunity against specific proteins in part because of their capacity to sequester antigen via B cell receptor (BCR). Our prior findings indicate that B cells can initiate an immune response in vivo to self proteins independent of other antigen-presenting cells (APC). However, these studies also demonstrated that both dendritic cells and macrophages are important in the ongoing immune response. The present work illustrates a mechanism by which antigen acquired by B cells through BCR is specifically transferred to other APC, in particular, macrophages. The transfer of antigen is dependent on the specificity of BCR and requires direct contact between the cells, but does not require MHC compatibility between the cells and is independent of the activation state of macrophages. Antigen transfer is functional, in that macrophages, which received B cell derived-antigen, can activate CD4 T cells. Overall, these results define a novel mechanism by which B cells can focus immunity toward a specific antigen and transfer the ability to activate CD4 T cells to other APC.

Increased competition for antigen during priming negatively impacts the generation of memory CD4 T cells

The factors involved in the differentiation of memory CD4 T cells from naïve precursors are poorly understood. We developed a system to examine the effect of increased competition for antigen by CD4 T cells on the generation of memory in response to infection with a recombinant vesicular stomatitis virus. Competition was initially regulated by increasing the precursor frequency of adoptively transferred naïve T cell antigen receptor transgenic CD4 T cells. Despite robust proliferation at high precursor frequencies, memory CD4 T cells did not develop, whereas decreasing the input number of naïve CD4 T cells promoted memory development after infection. The lack of memory development was linked to reduced blastogenesis and poor effector cell induction, but not to initial recruitment or proliferation of antigen-specific CD4 T cells. To prove that availability of antigen alone could regulate memory CD4 T cell development, we used treatment with an mAb specific for the epitope recognized by the transferred CD4 T cells. At high doses, this mAb effectively inhibited the antigen-specific CD4 T cell response. However, at a very low dose of mAb, primary CD4 T cell expansion was unaffected, although memory development was dramatically reduced. Moreover, the induction of effector function was concomitantly inhibited. Thus, competition for antigen during CD4 T cell priming is a major contributing factor to the development of the memory CD4 T cell pool.

Deficiency of fatty acid-binding proteins in mice confers protection from development of experimental autoimmune encephalomyelitis

Fatty acid-binding proteins (FABPs) act as intracellular receptors for a variety of hydrophobic compounds, enabling their diffusion within the cytoplasmic compartment. Recent studies have demonstrated the ability of FABPs to simultaneously regulate metabolic and inflammatory pathways. We investigated the role of adipocyte FABP and epithelial FABP in the development of experimental autoimmune encephalomyelitis to test the hypothesis that these FABPs impact adaptive immune responses and contribute to the pathogenesis of autoimmune disease. FABP-deficient mice exhibited a lower incidence of disease, reduced clinical symptoms of experimental autoimmune encephalomyelitis and dramatically lower levels of proinflammatory cytokine mRNA expression in CNS tissue as compared with wild-type mice. In vitro Ag recall responses of myelin oligodendrocyte glycoprotein 35-55-immunized FABP(-/-) mice showed reduced proliferation and impaired IFN-gamma production. Dendritic cells deficient for FABPs were found to be poor producers of proinflammatory cytokines and Ag presentation by FABP(-/-) dendritic cells did not promote proinflammatory T cell responses. This study reveals that metabolic-inflammatory pathway cross-regulation by FABPs contributes to adaptive immune responses and subsequent autoimmune inflammation.

Naive CD4(+) T cell frequency varies for different epitopes and predicts repertoire diversity and response magnitude

Cell-mediated immunity stems from the proliferation of naive T lymphocytes expressing T cell antigen receptors (TCRs) specific for foreign peptides bound to host major histocompatibility complex (MHC) molecules. Because of the tremendous diversity of the T cell repertoire, naive T cells specific for any one peptide:MHC complex (pMHC) are extremely rare. Thus, it is not known how many naive T cells of any given pMHC specificity exist in the body or how that number influences the immune response. By using soluble pMHC class II (pMHCII) tetramers and magnetic bead enrichment, we found that three different pMHCII-specific naive CD4(+) T cell populations vary in frequency from 20 to 200 cells per mouse. Moreover, naive population size predicted the size and TCR diversity of the primary CD4(+) T cell response after immunization with relevant peptide. Thus, variation in naive T cell frequencies can explain why some peptides are stronger immunogens than others.

An intense form of homeostatic proliferation of naive CD8+ cells driven by IL-2

In conditions of T lymphopenia, interleukin (IL) 7 levels rise and, via T cell receptor for antigen–self–major histocompatibility complex (MHC) interaction, induce residual naive T cells to proliferate. This pattern of lymphopenia-induced “homeostatic” proliferation is typically quite slow and causes a gradual increase in total T cell numbers and differentiation into cells with features of memory cells. In contrast, we describe a novel form of homeostatic proliferation that occurs when naive T cells encounter raised levels of IL-2 and IL-15 in vivo. In this situation, CD8⁺ T cells undergo massive expansion and rapid differentiation into effector cells, thus closely resembling the T cell response to foreign antigens. However, the responses induced by IL-2/IL-15 are not seen in MHC-deficient hosts, implying that the responses are driven by self-ligands. Hence, homeostatic proliferation of naive T cells can be either slow or fast, with the quality of the response to self being dictated by the particular cytokine (IL-7 vs. IL-2/IL-15) concerned. The relevance of the data to the gradual transition of naive T cells into memory-phenotype (MP) cells with age is discussed.

Spontaneous mammary tumors differ widely in their inherent sensitivity to adoptively transferred T cells

Immunotherapy of cancer can lead to the selection of antigen loss variants, which provides strong rationale to target oncogenes that are essential for tumor growth or viability. To investigate this concept, we tagged the HER2/neu oncogene with epitopes from ovalbumin to confer recognition by T-cell receptor transgenic CD8(+) (OT-I) and CD4(+) (OT-II) T cells. Transgenic mice expressing neu(OT-I/OT-II) developed mammary adenocarcinomas at 6 to 10 months of age. Adoptively transferred naive OT-I cells (with or without OT-II cells) proliferated vigorously on encountering neu(OT-I/OT-II)-expressing tumors. This was followed by the complete regression of 37% of tumors, whereas others showed partial/stable responses (40%) or progressive disease (23%). Those tumors undergoing complete regression never recurred. In mice with multiple primary tumors, simultaneous regressions and nonregressions were often seen, indicating that immune evasion occurred at a local rather than systemic level. The majority of nonregressing tumors expressed Neu(OT-I/OT-II) and MHC class I, and many avoided rejection through a profound block to T-cell infiltration. Thus, T cells directed against an essential oncogene can permanently eradicate a subset of spontaneous, established mammary tumors. However, in other tumors, local barriers severely limit the therapeutic response. To maximize the efficacy of immunotherapy against spontaneous cancers, predictive strategies that take into account the heterogeneity of the tumor microenvironment will be required.

c-Myb regulates lineage choice in developing thymocytes via its target gene Gata3

During T-cell development, thymocytes with intermediate avidity for antigen-MHC complexes are positively selected and then differentiate into functional cytotoxic and helper T cells. This process is controlled by signalling from the T-cell receptor (TCR). Here, we show that the c-Myb transcription factor is a critical downstream regulator of positive selection, promoting the development of helper T cells and blocking the development of cytotoxic T cells. A gain-of-function c-Myb transgene stops development of cytotoxic T cells, instead causing accumulation of a precursor population. Conversely, loss of c-Myb in selecting cells results in significantly fewer helper T cells. In c-Myb-null thymocytes, Gata3, a critical inducer of T-helper cell fate, is not upregulated in response to T-cell receptor signaling, following selection. We show that Gata3 is a direct target of c-Myb, and propose that c-Myb is an important regulator of Gata3, required for transduction of the T-cell receptor signal for subsequent helper cell lineage differentiation.

The inflamed central nervous system drives the activation and rapid proliferation of Foxp3+ regulatory T cells

Resolution of experimental autoimmune encephalomyelitis requires a large cohort of Foxp3(+) regulatory T cells (Tregs) within the CNS. In this study, we have used the passive transfer of murine experimental autoimmune encephalomyelitis using myelin-reactive T cells to study the development of this Treg response. Rapid proliferation of Tregs within the CNS (which is not seen in lymphoid organs) drives a switch in the balance of CNS proliferation from T effectors to Tregs, correlating with recovery. This proliferative burst drives a local over-representation of Vbeta8(+) Tregs in the CNS, indicative of an oligoclonal expansion. There is also evidence for a small, but detectable, myelin oligodendrocyte glycoprotein-reactive Treg component expanded without prior immunization. Furthermore, CNS-derived Tregs, taken during recovery, suppressed the proliferation of CNS-derived effectors in response to myelin oligodendrocyte glycoprotein. Under these conditions, Tregs could also limit the level of IFN-gamma production, but not IL-17 production, by CNS-derived effectors. These data establish the CNS as an environment that permits extensive Treg proliferation and are the first to demonstrate Treg expansion specifically within the tissues during the natural resolution of autoimmune inflammation.

The role of ICOS in the development of CD4 T cell help and the reactivation of memory T cells

We have addressed the role of the inducible costimulator (ICOS) in the development of T cell help for B cells and in the generation, survival and reactivation of memory CD4 T cells and B cells. We find that while T cell help for all antibody isotypes (including IgG2c) is impaired in ICOS knockout (ICOS-KO) mice, the IFN-gamma response is little affected, indicating a defect in helper function that is unrelated to cytokine production. In addition, the ICOS-negative T cells do not accumulate in B cell follicles. Secondary (memory), but not primary, clonal proliferation of antigen-specific B cells is impaired in ICOS-KO mice, as is the generation of secondary antibody-secreting cells. Analysis of endogenous CD4 memory cells in ICOS-KO mice, using MHC class II tetramers, reveals normal primary clonal expansion, formation of memory clones and long-term (10 wk) survival of memory cells, but defective expansion upon reactivation in vivo. The data point to a role of ICOS in supporting secondary, memory and effector T cell responses, possibly by influencing cell survival. The data also highlight differences in ICOS dependency of endogenous T cell proliferation in vivo compared to that of adoptively transferred TCR-transgenic T cells.

The vaccine adjuvant monophosphoryl lipid A as a TRIF-biased agonist of TLR4

The inflammatory toxicity of lipopolysaccharide (LPS), a component of bacterial cell walls, is driven by the adaptor proteins myeloid differentiation factor 88 (MyD88) and Toll-interleukin 1 receptor domain-containing adapter inducing interferon-beta (TRIF), which together mediate signaling by the endotoxin receptor Toll-like receptor 4 (TLR4). Monophosphoryl lipid A (MPLA) is a low-toxicity derivative of LPS with useful immunostimulatory properties, which is nearing regulatory approval for use as a human vaccine adjuvant. We report here that, in mice, the low toxicity of MPLA's adjuvant function is associated with a bias toward TRIF signaling, which we suggest is likely caused by the active suppression, rather than passive loss, of proinflammatory activity of this LPS derivative. This finding may have important implications for the development of future vaccine adjuvants.

Collagen distribution and expression of collagen-binding alpha1beta1 (VLA-1) and alpha2beta1 (VLA-2) integrins on CD4 and CD8 T cells during influenza infection

Most viral infections occur in extralymphoid tissues, yet the mechanisms that regulate lymphocytes in these environments are poorly understood. One feature common to many extralymphoid environments is an abundance of extracellular matrix. We have studied the expression of two members of the beta(1) integrin family of collagen-binding receptors, alpha(1)beta(1) and alpha(2)beta(1) (CD49a, VLA-1 and CD49b, VLA-2, respectively), on CD4 and CD8 T cells during the response to influenza infection in the lung. Flow cytometry showed that whereas T cells infiltrating the lung and airways can express both CD49a and CD49b, CD49a expression was most strongly associated with the CD8+ subset. Conversely, though fewer CD4+ T cells expressed CD49a, most CD4+ cells in the lung tissue or airways expressed CD49b. This reciprocal pattern suggested that CD4 and CD8 T cells might localize differently within the lung tissue and this was supported by immunofluorescent analysis. CD8+ cells tended to localize in close proximity to the collagen IV-rich basement membranes of either the airways or blood vessels, whereas CD4+ cells tended to localize in the collagen I-rich interstitial spaces, with few in the airways. These observations suggest that CD4 T cell interaction with the tissue microenvironment is distinct from CD8 T cells and support the concept that CD4+ T cells in peripheral tissues are regulated differently than the CD8 subset.

Elevation of intracellular cyclic AMP in alloreactive CD4(+) T Cells induces alloantigen-specific tolerance that can prevent GVHD lethality in vivo

Cyclic AMP (cAMP) is an important negative regulator of T cell activation, and an increased level of cAMP is associated with T cell hyporesponsiveness in vitro. We sought to determine whether elevating intracellular cAMP levels ex vivo in alloreactive T cells during primary mixed lymphocyte reactions (MLR) is sufficient to induce alloantigen-specific tolerance and prevent graft-versus-host disease (GVHD). Primary MLRs were treated with exogenous (8)Br-cAMP and IBMX, a compound that increases intracellular cAMP levels by inhibition of phosphodiesterases. T cell proliferation and IL-2 responsiveness in the treated primary MLR cultures were greatly reduced, and viable T cells recovered on day 8 also had impaired responses to restimulation with alloantigen compared to control-treated cells, but without an impairment to nonspecific mitogens. Labeling experiments showed that cAMP/IBMX inhibited alloreactive T cell proliferation by limiting the number of cell divisions, increasing susceptibility to apoptosis, and rendering nondeleted alloreactive T cells hyporesponsive to alloantigen restimulation. cAMP/IBMX-treated CD4(+) T cells had a markedly reduced capacity for GVHD lethality in major histocompatibility complex class II disparate recipients, but maintained the capacity to mediate other CD4(+) T cell responses in vivo. Thus, our results provide the first preclinical evidence of using cAMP-elevating pharmaceutical reagents to achieve long-term alloantigen-specific T cell tolerance that is sufficient to prevent GVHD.

L-selectin-negative CCR7- effector and memory CD8+ T cells enter reactive lymph nodes and kill dendritic cells

T lymphocytes lacking the lymph node-homing receptors L-selectin and CCR7 do not migrate to lymph nodes in the steady state. Instead, we found here that lymph nodes draining sites of mature dendritic cells or adjuvant inoculation recruited L-selectin-negative CCR7- effector and memory CD8+ T cells. This recruitment required CXCR3 expression on T cells and occurred through high endothelial venules in concert with lumenal expression of the CXCR3 ligand CXCL9. In reactive lymph nodes, recruited T cells established stable interactions with and killed antigen-bearing dendritic cells, limiting the ability of these dendritic cells to activate naive CD4+ and CD8+ T cells. The inducible recruitment of blood-borne effector and memory T cells to lymph nodes may represent a mechanism for terminating primary and limiting secondary immune responses.

A novel pathway that regulates inflammatory disease in the respiratory tract

In animals with acute airway inflammation followed by repeated exposure to inhaled Ag, inflammation wanes over time and thus limits the study of chronic airway inflammatory diseases such as asthma. We developed a model of airway inflammation and inhalational exposure to investigate regulatory pathways in the respiratory tract. We show that Th1- and Th2-induced airway inflammation followed by repeated exposure to inhaled Ag leads to a state of immunosuppression. Challenge of these animals with a marked population of TCR transgenic effector Th1 or Th2 cells results in a striking inhibition of inflammation and effector Th cells. In Th2 models, airway hyperresponsiveness, mucus, and eosinophilia are reduced. The inhibitory effects observed are Ag nonspecific, can be induced in lymphocyte-deficient mice, and are associated with a population of TGF-beta1-expressing macrophages. Induction of this pathway may offer potent localized treatment of chronic T cell-mediated respiratory illnesses and provide insights into the development of such diseases.

Cyclic adenosine monophosphate is a key component of regulatory T cell-mediated suppression

Naturally occurring regulatory T cells (T reg cells) are a thymus-derived subset of T cells, which are crucial for the maintenance of peripheral tolerance by controlling potentially autoreactive T cells. However, the underlying molecular mechanisms of this strictly cell contact–dependent process are still elusive. Here we show that naturally occurring T reg cells harbor high levels of cyclic adenosine monophosphate (cAMP). This second messenger is known to be a potent inhibitor of proliferation and interleukin 2 synthesis in T cells. Upon coactivation with naturally occurring T reg cells the cAMP content of responder T cells is also strongly increased. Furthermore, we demonstrate that naturally occurring T reg cells and conventional T cells communicate via cell contact–dependent gap junction formation. The suppressive activity of naturally occurring T reg cells is abolished by a cAMP antagonist as well as by a gap junction inhibitor, which blocks the cell contact–dependent transfer of cAMP to responder T cells. Accordingly, our results suggest that cAMP is crucial for naturally occurring T reg cell–mediated suppression and traverses membranes via gap junctions. Hence, naturally occurring T reg cells unexpectedly may control the immune regulatory network by a well-known mechanism based on the intercellular transport of cAMP via gap junctions.

Mast cell-derived TNF contributes to airway hyperreactivity, inflammation, and TH2 cytokine production in an asthma model in mice

BACKGROUND

Mast cells, IgE, and TNF, which have been implicated in human atopic asthma, contribute significantly to the allergic airway inflammation induced by ovalbumin (OVA) challenge in mice sensitized with OVA without alum. However, it is not clear to what extent mast cells represent a significant source of TNF in this mouse model.

OBJECTIVE

We investigated the importance of mast cell-derived TNF in a mast cell-dependent model of OVA-induced airway hyperreactivity (AHR) and allergic airway inflammation.

METHODS

Features of this model of airway inflammation were analyzed in C57BL/6J-wild-type mice, mast cell-deficient C57BL/6J-Kit(W-sh)(/W-sh) mice, and C57BL/6J Kit(W-sh/W-sh) mice that had been systemically engrafted with bone marrow-derived cultured mast cells from C57BL/6J-wild-type or C57BL/6J-TNF(-/-) mice.

RESULTS

Ovalbumin-induced AHR and airway inflammation were significantly reduced in mast cell-deficient Kit(W-sh/W-sh) mice versus wild-type mice. By contrast, Kit(W-sh/W-sh) mice that had been engrafted with wild-type but not with TNF(-/-) bone marrow-derived cultured mast cells exhibited responses very similar to those observed in wild-type mice. Mast cells and mast cell-derived TNF were not required for induction of OVA-specific memory T cells in the sensitization phase, but significantly enhanced lymphocyte recruitment and T(H)2 cytokine production in the challenge phase.

CONCLUSION

Mast cell-derived TNF contributes significantly to the pathogenesis of mast cell-dependent and IgE-dependent, OVA-induced allergic inflammation and AHR in mice, perhaps in part by enhancing lymphocyte recruitment and T(H)2 cytokine production.

CLINICAL IMPLICATIONS

Our findings in mice support the hypothesis that mast cell-derived TNF can promote allergic inflammation and AHR in asthma.

Lipopolysaccharide enhances in vivo interleukin-2 production and proliferation by naive antigen-specific CD4 T cells via a Toll-like receptor 4-dependent mechanism

Microbial adjuvants are essential for the development of T-cell-dependent antibody production, recall T-cell proliferation and interferon-gamma production following immunization with protein antigens. Using an adoptive transfer approach, we showed that the adjuvant lipopolysaccharide enhanced the frequency of cells producing interleukin-2, enhanced clonal expansion by antigen-specific CD4 T cells and increased CD86 and interleukin-1alpha production by antigen-presenting cells. All of these effects were dependent on Toll-like receptor-4 (TLR4) expression by cells other than the antigen-specific CD4 T cells. The ability of lipopolysaccharides to increase the number of antigen-specific CD4 T cells that survive after immunization probably explains the previous finding that antigen-specific proliferation by T cells from normal mice depends on previous exposure to antigen and adjuvant.

Expression of lymphotoxin-alphabeta on antigen-specific T cells is required for DC function

During an immune response, activated antigen (Ag)-specific T cells condition dendritic cells (DCs) to enhance DC function and survival within the inflamed draining lymph node (LN). It has been difficult to ascertain the role of the tumor necrosis factor (TNF) superfamily member lymphotoxin-αβ (LTαβ) in this process because signaling through the LTβ-receptor (LTβR) controls multiple aspects of lymphoid tissue organization. To resolve this, we have used an in vivo system where the expression of TNF family ligands is manipulated only on the Ag-specific T cells that interact with and condition Ag-bearing DCs. We report that LTαβ is a critical participant required for optimal DC function, independent of its described role in maintaining lymphoid tissue organization. In the absence of LTαβ or CD40L on Ag-specific T cells, DC dysfunction could be rescued in vivo via CD40 or LTβR stimulation, respectively, suggesting that these two pathways cooperate for optimal DC conditioning.

Constraints in antigen presentation severely restrict T cell recognition of the allogeneic fetus

How the fetus escapes rejection by the maternal immune system remains one of the major unsolved questions in transplantation immunology. Using a system to visualize both CD4+ and CD8+ T cell responses during pregnancy in mice, we find that maternal T cells become aware of the fetal allograft exclusively through "indirect" antigen presentation, meaning that T cell engagement requires the uptake and processing of fetal/placental antigen by maternal APCs. This reliance on a relatively minor allorecognition pathway removes a major threat to fetal survival, since it avoids engaging the large number of T cells that typically drive acute transplant rejection through their ability to directly interact with foreign MHC molecules. Furthermore, CD8+ T cells that indirectly recognize fetal/placental antigen undergo clonal deletion without priming for cytotoxic effector function and cannot induce antigen-specific fetal demise even when artificially activated. Antigen presentation commenced only at mid-gestation, in association with the endovascular invasion of placental trophoblasts and the hematogenous release of placental debris. Our results suggest that limited pathways of antigen presentation, in conjunction with tandem mechanisms of immune evasion, contribute to the unique immunological status of the fetus. The pronounced degree of T cell ignorance of the fetus also has implications for the pathophysiology of immune-mediated early pregnancy loss.

MHC class II deprivation impairs CD4 T cell motility and responsiveness to antigen-bearing dendritic cells in vivo

The role continuous contact with self-peptide/MHC molecules (self ligands) in the periphery plays in the function of mature T cells remains unclear. Here, we elucidate a role for MHC class II molecules in T cell trafficking and antigen responsiveness in vivo. We find that naïve CD4 T cells deprived of MHC class II molecules demonstrate a progressive and profound defect in motility (measured by real-time two-photon imaging) and that these cells have a decreased ability to interact with limiting numbers of cognate antigen-bearing dendritic cells, but they do not demonstrate a defect in their responsiveness to direct stimulation with anti-CD3 monoclonal antibody. Using GST fusion proteins, we show that MHC class II availability promotes basal activation of Rap1 and Rac1 but does not alter the basal activity of Ras. We propose that tonic T cell receptor signaling from self-ligand stimulation is required to maintain a basal state of activation of small guanosine triphosphatases critical for normal T cell motility and that T cell motility is critical for the antigen receptivity of naïve CD4 T cells. These studies suggest a role for continuous self-ligand stimulation in the periphery for the maintenance and function of mature naïve CD4 T cells.

Naive B cells generate regulatory T cells in the presence of a mature immunologic synapse

Naive B cells are ineffective antigen-presenting cells and are considered unable to activate naive T cells. However, antigen-specific contact of these cells leads to stable cell pairs that remain associated over hours in vivo. The physiologic role of such pairs has not been evaluated. We show here that antigen-specific conjugates between naive B cells and naive T cells display a mature immunologic synapse in the contact zone that is absent in T-cell-dendritic-cell (DC) pairs. B cells induce substantial proliferation but, contrary to DCs, no loss of L-selectin in T cells. Surprisingly, while DC-triggered T cells develop into normal effector cells, B-cell stimulation over 72 hours induces regulatory T cells inhibiting priming of fresh T cells in a contact-dependent manner in vitro. In vivo, the regulatory T cells home to lymph nodes where they potently suppress immune responses such as in cutaneous hypersensitivity and ectopic allogeneic heart transplant rejection. Our finding might help to explain old observations on tolerance induction by B cells, identify the mature immunologic synapse as a central functional module of this process, and suggest the use of naive B-cell-primed regulatory T cells, "bTregs," as a useful approach for therapeutic intervention in adverse adaptive immune responses.

Semaphorin 7A initiates T-cell-mediated inflammatory responses through alpha1beta1 integrin

Semaphorins are axon guidance factors that assist growing axons in finding appropriate targets and forming synapses. Emerging evidence suggests that semaphorins are involved not only in embryonic development but also in immune responses. Semaphorin 7A (Sema7A; also known as CD108), which is a glycosylphosphatidylinositol-anchored semaphorin, promotes axon outgrowth through beta1-integrin receptors and contributes to the formation of the lateral olfactory tract. Although Sema7A has been shown to stimulate human monocytes, its function as a negative regulator of T-cell responses has also been reported. Thus, the precise function of Sema7A in the immune system remains unclear. Here we show that Sema7A, which is expressed on activated T cells, stimulates cytokine production in monocytes and macrophages through alpha1beta1 integrin (also known as very late antigen-1) as a component of the immunological synapse, and is critical for the effector phase of the inflammatory immune response. Sema7A-deficient (Sema7a-/-) mice are defective in cell-mediated immune responses such as contact hypersensitivity and experimental autoimmune encephalomyelitis. Although antigen-specific and cytokine-producing effector T cells can develop and migrate into antigen-challenged sites in Sema7a-/- mice, Sema7a-/- T cells fail to induce contact hypersensitivity even when directly injected into the antigen-challenged sites. Thus, the interaction between Sema7A and alpha1beta1 integrin is crucial at the site of inflammation. These findings not only identify a function of Sema7A as an effector molecule in T-cell-mediated inflammation, but also reveal a mechanism of integrin-mediated immune regulation.

Regulatory T cells interfere with the development of bronchus-associated lymphoid tissue

Presence and extent of bronchus-associated lymphoid tissue (BALT) is subject to considerable variations between species and is only occasionally observed in lungs of mice. Here we demonstrate that mice deficient for the chemokine receptor CCR7 regularly develop highly organized BALT. These structures were not present at birth but were detectable from day 5 onwards. Analyzing CCR7^−/−/wild-type bone marrow chimeras, we demonstrate that the development of BALT is caused by alterations of the hematopoietic system in CCR7-deficient mice. These observations together with the finding that CCR7-deficient mice posses dramatically reduced numbers of regulatory T cells (T reg cells) in the lung-draining bronchial lymph node suggest that BALT formation might be caused by disabled in situ function of T reg cells. Indeed, although adoptive transfer of wild-type T reg cells to CCR7-deficient recipients resulted in a profound reduction of BALT formation, neither naive wild-type T cells nor T reg cells from CCR7^−/− donors impair BALT generation. Furthermore, we provide evidence that CCR7-deficient T reg cells, although strongly impaired in homing to peripheral lymph nodes, are fully effective in vitro. Thus our data reveal a CCR7-dependent homing of T reg cells to peripheral lymph nodes in conjunction with a role for these cells in controlling BALT formation.

Cutting Edge: Chemokine receptor CCR4 is necessary for antigen-driven cutaneous accumulation of CD4 T cells under physiological conditions

Dual expression of chemokine receptor CCR4 and E-selectin ligand is characteristic of skin-tropic CD4 T cells from blood, lymphoid organs, and the skin itself. A strong and specific correlation exists among CCR4, its ligand CCL17/TARC, and the cutaneous lymphocyte-homing process. Nevertheless, whether CCR4 function is required for skin-specific trafficking remains an open question, which we address in this study. We developed an Ag-specific, TCR-transgenic, murine CD4 T cell adoptive transfer model that induces a mixed Th1 and Th17 cutaneous response. Within the hosts, both CCR4(+/+) and CCR4(-/-) donor CD4 T cells contribute equally well to the circulating E-selectin ligand(+) pool in response to Ag. However, only CCR4(+/+) donor cells accumulate efficiently within the skin. CCR4(-/-) cells home normally to the peritoneum, showing that they do not have a general defect in lymphocyte trafficking. We conclude that under physiological conditions, CCR4 is a nonredundant, necessary component of skin-specific lymphocyte trafficking.

IL-6 produced by dendritic cells from lupus-prone mice inhibits CD4+CD25+ T cell regulatory functions

The B6.Sle1.Sle2.Sle3 triple congenic mouse (B6.TC) is a model of lupus coexpressing the three major NZM2410-derived susceptibility loci on a C57BL/6 background. B6.TC mice produce high titers of antinuclear nephrogenic autoantibodies and a highly penetrant glomerulonephritis. Previous studies have shown the Sle1 locus is associated with a reduced number of regulatory T cells (Treg) and that Sle3 results in intrinsic defects of myeloid cells that hyperactivate T cells. In this report, we show that B6.TC dendritic cells (DCs) accumulate in lymphoid organs and present a defective maturation process, in which bone marrow-derived, plasmacytoid, and myeloid DCs express a significantly lower level of CD80, CD86, and MHC class II. B6.TC DCs also induce a higher level of proliferation in CD4(+) T cells than B6 DCs, and B6.TC DCs block the suppressive activity of Treg. B6.TC DCs overproduce IL-6, which is necessary for the blockade of Treg activity, as shown by the effect of anti-IL-6 neutralizing Ab in the suppression assays. The overproduction of IL-6 by DCs and the blockade of Treg activity maps to Sle1, which therefore not only confers a reduced number of Treg but also blocks their ability to regulate autoreactive T cells. Taken together, these results provide a genetic and mechanistic evidence for systemic autoimmunity resulting from an impaired regulatory T cell compartment in both number and function and for Sle1-expressing DCs playing a major role in the latter defect though their production of IL-6.

Bcl10/Malt1 signaling is essential for TCR-induced NF-kappaB activation in thymocytes but dispensable for positive or negative selection

During T cell development in the thymus, high-affinity/avidity TCR engagement induces negative selection by apoptosis, while lower affinity/avidity TCR interactions lead to positive selection and survival of thymocytes. Yet, the mechanisms that discriminate between positive and negative selection are not fully understood. One major regulator of survival and apoptosis in lymphoid cells is the transcription factor NF-kappaB. Several reports have indicated key roles for NF-kappaB in positive and negative selection. In peripheral T cells, TCR ligation activates NF-kappaB through a selective pathway that involves protein kinase Ctheta, Bcl10, and Malt1. While protein kinase Ctheta is dispensable for thymic TCR signaling, the molecular roles of Bcl10 and Malt1 in thymocytes have not been investigated. In the present study, we show that both Bcl10 and Malt1 are essential for TCR signaling in thymocytes as a genetic disruption of either molecule blocks TCR-induced NF-kappaB activation in these cells. To investigate the function of this pathway in thymic selection, we introduced the Bcl10 or Malt1 mutations into three well-established TCR transgenic mouse models. Surprisingly, using several in vivo or in vitro assays, we were unable to demonstrate a role for TCR-induced NF-kappaB activation in either positive or negative selection. Thus, while TCR signaling to NF-kappaB controls the activation of mature T cells, we suggest that this pathway is not involved in the positive or negative selection of thymocytes.

Chemokine-guided CD4+ T cell help enhances generation of IL-6RalphahighIL-7Ralpha high prememory CD8+ T cells

CD4(+) T cells promote effective CD8(+) T cell-mediated immunity, but the timing and mechanistic details of such help remain controversial. Furthermore, the extent to which innate stimuli act independently of help in enhancing CD8(+) T cell responses is also unresolved. Using a noninfectious vaccine model in immunocompetent mice, we show that even in the presence of innate stimuli, CD4(+) T cell help early after priming is required for generating an optimal pool of functional memory CD8(+) T cells. CD4(+) T cell help increased the size of a previously unreported population of IL-6Ralpha(high)IL-7Ralpha(high) prememory CD8(+) T cells shortly after priming that showed a survival advantage in vivo and contributed to the majority of functional memory CD8(+) T cells after the contraction phase. In accord with our recent demonstration of chemokine-guided recruitment of naive CD8(+) T cells to sites of CD4(+) T cell-dendritic cell interactions, the generation of IL-6Ralpha(high)IL-7Ralpha(high) prememory as well as functional memory CD8(+) T cells depended on the early postvaccination action of the inflammatory chemokines CCL3 and CCL4. Together, these findings support a model of CD8(+) T cell memory cell differentiation involving the delivery of key signals early in the priming process based on chemokine-guided attraction of naive CD8(+) T cells to sites of Ag-driven interactions between TLR-activated dendritic cells and CD4(+) T cells. They also reveal that elevated IL-6Ralpha expression by a subset of CD8(+) T cells represents an early imprint of CD4(+) T cell helper function that actively contributes to the survival of activated CD8(+) T cells.

Phenotypic differences between Th1 and Th17 cells and negative regulation of Th1 cell differentiation by IL-17

Recent evidence from several groups indicates that IL-17-producing Th17 cells, rather than, as once was thought, IFN-gamma-producing Th1 cells, can represent the key effector cells in the induction/development of several autoimmune and allergic disorders. Although Th17 cells exhibit certain phenotypic and developmental differences from Th1 cells, the extent of the differences between these two T cell subsets is still not fully understood. We found that the expression profile of cell surface molecules on Th17 cells has more similarities to that of Th1 cells than Th2 cells. However, although certain Th1-lineage markers [i.e., IL-18 receptor alpha, CXCR3, and T cell Ig domain, mucin-like domain-3 (TIM-3)], but not Th2-lineage markers (i.e., T1/ST2, TIM-1, and TIM-2), were expressed on Th17 cells, the intensity of expression was different between Th17 and Th1 cells. Moreover, the expression of CTLA-1, ICOS, programmed death ligand 1, CD153, Fas, and TNF-related activation-induced cytokine was greater on Th17 cells than on Th1 cells. We found that IL-23 or IL-17 can suppress Th1 cell differentiation in the presence of exogenous IL-12 in vitro. We also confirmed that IL-12 or IFN-gamma can negatively regulate Th17 cell differentiation. However, these cytokines could not modulate such effects on T cell differentiation in the absence of APC.

Distinct Differentiation Potential of Blood Monocyte Subsets in the Lung

Peripheral blood monocytes are a population of circulating mononuclear phagocytes that harbor potential to differentiate into macrophages and dendritic cells. As in humans, monocytes in the mouse comprise two phenotypically distinct subsets that are Gr1(high)CX(3)CR1(int) and Gr1(low)CX(3)CR1(high), respectively. The question remains whether these populations contribute differentially to the generation of peripheral mononuclear phagocytes. In this study, we track the fate of adoptively transferred, fractionated monocyte subsets in the lung of recipient mice. We show that under inflammatory and noninflammatory conditions, both monocyte subsets give rise to pulmonary dendritic cells. In contrast, under the conditions studied, only Gr1(low)CX(3)CR1(high) monocytes, but not Gr1(high)CX(3)CR1(int) cells, had the potential to differentiate into lung macrophages. However, Gr1(high)CX(3)CR1(int) monocytes could acquire this potential upon conversion into Gr1(low)CX(3)CR1(high) cells. Our results therefore indicate an intrinsic dichotomy in the differentiation potential of the two main blood monocyte subsets.

Cognate CD4+ Help Elicited by Resting Dendritic Cells Does Not Impair the Induction of Peripheral Tolerance in CD8+ T Cells

Peripheral tolerance is required to prevent autoimmune tissue destruction by self-reactive T cells that escape negative selection in the thymus. One mechanism of peripheral tolerance in CD8(+) T cells is their activation by resting dendritic cells (DC). In contrast, DC can be "licensed" by CD4(+) T cells to induce cytotoxic function in CD8(+) T cells. The question that then arises, whether CD4(+) T cell help could impair peripheral tolerance induction in self-reactive CD8(+) T cells, has not been addressed. In this study we show that CD4(+) T cell activation by resting DC results in helper function that transiently promotes the expansion and differentiation of cognate CD8(+) T cells. However, both the CD4(+) and CD8(+) T cell populations ultimately undergo partial deletion and acquire Ag unresponsiveness, disabling their ability to destroy OVA-expressing pancreatic beta cells and cause diabetes. Thus, effective peripheral tolerance can be induced by resting DC in the presence of CD4(+) and CD8(+) T cells with specificity for the same Ag.

Cross-presentation of antigens from apoptotic tumor cells by liver sinusoidal endothelial cells leads to tumor-specific CD8+ T cell tolerance

Development of tumor-specific T cell tolerance contributes to the failure of the immune system to eliminate tumor cells. Here we report that hematogenous dissemination of tumor cells followed by their elimination and local removal of apoptotic tumor cells in the liver leads to subsequent development of T cell tolerance towards antigens associated with apoptotic tumor cells. We provide evidence that liver sinusoidal endothelial cells (LSEC) remove apoptotic cell fragments generated by induction of tumor cell apoptosis through hepatic NK1.1+ cells. Antigen associated with apoptotic cell material is processed and cross-presented by LSEC to CD8+ T cells, leading to induction of CD8+ T cell tolerance. Adoptive transfer of LSEC isolated from mice challenged previously with tumor cells promotes development of CD8+ T cell tolerance towards tumor-associated antigen in vivo. Our results indicate that hematogenous dissemination of tumor cells, followed by hepatic tumor cell elimination and local cross-presentation of apoptotic tumor cells by LSEC and subsequent CD8+ T cell tolerance induction, represents a novel mechanism operative in tumor immune escape.

A newly established murine immature dendritic cell line can be differentiated into a mature state, but exerts tolerogenic function upon maturation in the presence of glucocorticoid

The phenotype and function of murine dendritic cells (DCs) are primarily studied using bone-marrow–derived DCs (BM-DCs), but may be hampered by the heterogenous phenotype of BM-DCs due to their differential state of maturation. Here we characterize a newly established murine DC line (SP37A3) of myeloid origin. During maintainance in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and M-CSF, SP37A3 cells resemble immature DCs characterized by low expression of major histocompatibility complex (MHC) II and costimulatory molecules and low T-cell stimulatory capacity. Upon stimulation, SP37A3 cells acquire a mature phenotype and activate naive T cells as potently as BM-DCs. Similar to BM-DCs, SP37A3 cells activated in the presence of dexamethasone-induced regulatory T cells, which were anergic upon restimulation and suppressed proliferation of naive T cells. This tolerogenic state was reflected by lower expression levels of costimulatory molecules and proinflammatory cytokines compared with mature cells, as well as up-regulated expression of FcγRIIB and interleukin-1RA (IL-1RA). SP37A3 cells were responsive to dexamethasone even when applied at later time points during activation, suggesting functional plasticity. Thus, DC line SP37A3 represents a suitable model to study functions of immature and mature as well as tolerogenic myeloid DCs, circumventing restrictions associated with the use of primary DCs and BM-DCs.

Disruption of Innate-Mediated Proinflammatory Cytokine and Reactive Oxygen Species Third Signal Leads to Antigen-Specific Hyporesponsiveness

Successful Ag activation of naive T helper cells requires at least two signals consisting of TCR and CD28 on the T cell interacting with MHC II and CD80/CD86, respectively, on APCs. Recent evidence demonstrates that a third signal consisting of proinflammatory cytokines and reactive oxygen species (ROS) produced by the innate immune response is important in arming the adaptive immune response. In an effort to curtail the generation of an Ag-specific T cell response, we targeted the synthesis of innate immune response signals to generate Ag-specific hyporesponsiveness. We have reported that modulation of redox balance with a catalytic antioxidant effectively inhibited the generation of third signal components from the innate immune response (TNF-alpha, IL-1beta, ROS). In this study, we demonstrate that innate immune-derived signals are necessary for adaptive immune effector function and disruption of these signals with in vivo CA treatment conferred Ag-specific hyporesponsiveness in BALB/c, NOD, DO11.10, and BDC-2.5 mice after immunization. Modulating redox balance led to decreased Ag-specific T cell proliferation and IFN-gamma synthesis by diminishing ROS production in the APC, which affected TNF-alpha levels produced by CD4(+) T cells and impairing effector function. These results demonstrate that altering redox status can be effective in T cell-mediated diseases such as autoimmune diabetes to generate Ag-specific immunosuppression because it inhibits the third signal necessary for CD4(+) T cells to transition from expansion to effector function.