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

Oral Treatment with Extract of Agaricus blazei Murill Enhanced Th1 Response through Intestinal Epithelial Cells and Suppressed OVA-Sensitized Allergy in Mice

To clarify the mechanism of the antiallergic activity of Agaricus blazei Murill extract (ABME), the present paper used an in vivo allergy model and an in vitro intestinal gut model. During OVA sensitization, the serum IgE levels decreased significantly in ABME group. Interleukin (IL)-4 and -5 produced from OVA-restimulated splenocytes was significantly decreased, and anti-CD3ε/CD28 antibody treatment also reduced IL-10, -4, and -5 production and increased IFN-γ production in ABME group. These results suggest that oral administration of ABME improves Th1/Th2 balance. Moreover, a coculture system constructed of Caco-2 cells and splenocytes from OT-II mice or RAW 264.7 cells indicated that the significant increases in IFN-γ production by ABME treatment. Therefore, it was concluded that the antiallergic activity of ABME was due to the activation of macrophages by epithelial cells and the promotion of the differentiation of naïve T cells into Th1 cells in the immune.

Basophils orchestrate chronic allergic dermatitis and protective immunity against helminths

Basophils are associated with T helper 2 (Th2) cell-polarized immune responses such as allergic disorders or helminth infections. To directly address the role of basophils for type 2 immunity, we generated transgenic mice with constitutive and selective deletion of basophils. Differentiation and accumulation of Th2 cells, induction of eosinophilia, and increase in serum IgE or IgG1 induced by allergens or by infection with the helminth Nippostrongylus brasiliensis appeared to be basophil independent. Further, basophils were not required for passive IgE- or IgG1-mediated systemic anaphylaxis. However, basophils were essential for IgE-meditated chronic allergic dermatitis and for protection against secondary infection with N. brasiliensis. These results demonstrate that basophils play an important role for protective immunity against helminths and orchestrate chronic allergic inflammation, whereas primary Th2 cell responses can operate efficiently in the absence of this cell type.

Vaccines delivered by integration-deficient lentiviral vectors targeting dendritic cells induces strong antigen-specific immunity

We report a study of an integration-deficient lentiviral vector (IDLV) enveloped with a Sindbis virus glycoprotein mutant (SVGmu) capable of selectively binding to dendritic cells (DCs) for its potential as a vaccine carrier. The in vitro assays showed that the D64V point mutation in the catalytic domain of HIV-1 integrase efficiently inhibited the integration of the transgene upon vector transduction, while the targeting specificity of the vector to preferentially transduce and mediate durable expression in DCs was maintained. Substantial immune responses in C57BL/6 mice and complete protection against a challenge with the C57BL/6 thymoma EG.7 tumor expressing a delivered ovalbumin (OVA) antigen in mice have been achieved through the direct injection of the DC-directed IDLV encoding OVA. Thus, this DC-directed IDLV system represents a promising and efficient vector platform with remarkably improved safety for the future development of DC-based immunotherapy.

Negative selection and peptide chemistry determine the size of naive foreign peptide-MHC class II-specific CD4+ T cell populations

Naive CD4(+) T cell populations that express TCRs specific for different foreign peptide-MHC class II complex (pMHCII) ligands can vary in size over several orders of magnitude. This variation may explain why immune responses to some peptides are stronger than others. In this study, we used a sensitive pMHCII-tetramer-based cell enrichment method to study the derivation of two naive foreign pMHCII-specific naive CD4(+) T cell populations that differed in size by 8-fold in normal mice. Analysis of mice in which thymic negative selection was impaired revealed that the smaller population underwent more clonal deletion than the larger population. In addition, large naive cell populations tended to recognize peptides with tryptophan residues as TCR contacts. Thus, the foreign pMHCII that tend to be recognized by large naive populations induce minimal clonal deletion and contain certain amino acids with the capacity to interact favorably with TCRs.

Cutting edge: TCR ligation triggers digital activation of NF-kappaB

TCR-mediated activation of the transcription factor NF-κB is required for T cell proliferation, survival, and effector differentiation. Although this pathway is the subject of intense study, it is not known whether TCR signaling to NF-κB is digital (switch-like) or analog in nature. Through analysis of the phosphorylation and degradation of IκBα and the nuclear translocation and phosphorylation of the NF-κB subunit RelA, we show that TCR-directed NF-κB activation is digital. Furthermore, digitization occurs well upstream of the IκB kinase complex, as protein kinase C translocation to the immunologic synapse and activation-associated aggregation of Bcl10 and Malt1 also demonstrate both digital behavior and high correlation with RelA nuclear translocation. Thus, similar to the TCR-to-MAPK signaling cascade, analog Ag inputs are converted to digital activation outputs to NF-κB at an early step downstream of TCR ligation.

The phosphatase PTP-PEST promotes secondary T cell responses by dephosphorylating the protein tyrosine kinase Pyk2

PTP-PEST (encoded by Ptpn12) is an intracellular protein tyrosine phosphatase belonging to the same family as LYP. LYP inhibits secondary T cell responses by suppressing Src family protein tyrosine kinases and is implicated in human autoimmunity. To determine the function of PTP-PEST in T cells, we generated mice with a conditionally deleted allele of Ptpn12. By removing PTP-PEST in T cells, we determined that PTP-PEST was not necessary for T cell development or primary responses. However, PTP-PEST was required for secondary T cell responses, anergy prevention, and autoimmunity induction. PTP-PEST specifically regulated the phosphorylation of Pyk2, a substrate of the Src family kinase Fyn. It also promoted the formation of T cell homoaggregates, which are known to enhance T cell activation. Thus, PTP-PEST controls Pyk2 activity and is a positive regulator of secondary T cell activation. These data illustrate the critical role of protein tyrosine phosphatases in T cell regulation.

H2-O, a MHC class II-like protein, sets a threshold for B-cell entry into germinal centers

Upon antigen (Ag) encounter, B cells require T-cell help to enter the germinal center (GC). They obtain this help by presenting Ag-derived peptides on MHC class II (MHCII) for recognition by the T-cell receptor (TCR) of CD4(+) T cells. Peptides are loaded onto MHCII in endosomal compartments in a process catalyzed by the MHCII-like protein H2-M (HLA-DM in humans). This process is modulated by another MHCII-like protein, H2-O (HLA-DO in humans). H2-O is a biochemical inhibitor of peptide loading onto MHCII; however, on the cellular level, it has been shown to have varying effects on Ag presentation. Thus, the function of H2-O in the adaptive immune response remains unclear. Here, we examine the effect of H2-O expression on the ability of Ag-specific B cells to enter the GC. We show that when Ag specific WT and H2-O(-/-) B cells are placed in direct competition, H2-O(-/-) B cells preferentially populate the GC. This advantage is confined to Ag-specific B cells and is due to their superior ability to obtain Ag-specific T-cell help when T-cell help is limiting. Overall, our work shows that H2-O expression reduces the ability of B cells to gain T-cell help and participate in the GC reaction.

Follicular helper T cell differentiation requires continuous antigen presentation that is independent of unique B cell signaling

Effective humoral immunity depends on the support of B cell responses by T follicular helper (Tfh) cells. Although it has been proposed that Tfh cell differentiation requires T-B interactions, the relative contribution of specific populations of Ag-presenting cells remains unknown. We employed three independent strategies that compromised interactions between CD4(+) T cells and activated B cells in vivo. Whereas the expansion of CD4(+) T cells was relatively unaffected, Tfh cell differentiation was completely blocked in all scenarios. Surprisingly, augmenting antigen presentation by non-B cells rescued Tfh cell differentiation, as determined by surface phenotype, gene expression, and germinal center localization. We conclude that although Ag presentation by responding B cells is typically required for the generation of Tfh cells, this does not result from the provision of a unique B cell-derived signal, but rather because responding B cells rapidly become the primary source of antigen.

Immune-mediated mechanisms of parasite tissue sequestration during experimental cerebral malaria

Cerebral malaria is a severe complication of malaria. Sequestration of parasitized RBCs in brain microvasculature is associated with disease pathogenesis, but our understanding of this process is incomplete. In this study, we examined parasite tissue sequestration in an experimental model of cerebral malaria (ECM). We show that a rapid increase in parasite biomass is strongly associated with the induction of ECM, mediated by IFN-gamma and lymphotoxin alpha, whereas TNF and IL-10 limit this process. Crucially, we discovered that host CD4(+) and CD8(+) T cells promote parasite accumulation in vital organs, including the brain. Modulation of CD4(+) T cell responses by helminth coinfection amplified CD4(+) T cell-mediated parasite sequestration, whereas vaccination could generate CD4(+) T cells that reduced parasite biomass and prevented ECM. These findings provide novel insights into immune-mediated mechanisms of ECM pathogenesis and highlight the potential of T cells to both prevent and promote infectious diseases.

MHC class II-restricted antigen presentation by plasmacytoid dendritic cells inhibits T cell-mediated autoimmunity

Although plasmacytoid dendritic cells (pDCs) express major histocompatibility complex class II (MHCII) molecules, and can capture, process, and present antigens (Ags), direct demonstrations that they function as professional Ag-presenting cells (APCs) in vivo during ongoing immune responses remain lacking. We demonstrate that mice exhibiting a selective abrogation of MHCII expression by pDCs develop exacerbated experimental autoimmune encephalomyelitis (EAE) as a consequence of enhanced priming of encephalitogenic CD4⁺ T cell responses in secondary lymphoid tissues. After EAE induction, pDCs are recruited to lymph nodes and establish MHCII-dependent myelin-Ag–specific contacts with CD4⁺ T cells. These interactions promote the selective expansion of myelin-Ag–specific natural regulatory T cells that dampen the autoimmune T cell response. pDCs thus function as APCs during the course of EAE and confer a natural protection against autoimmune disease development that is mediated directly by their ability to present of Ags to CD4⁺ T cells in vivo.

Lipid accumulation and dendritic cell dysfunction in cancer

Dendritic cells (DCs), a type of professional antigen-presenting cells, are responsible for initiation and maintenance of immune responses. Here we report that a substantial proportion of DCs in tumor-bearing mice and people with cancer have high amounts of triglycerides as compared with DCs from tumor-free mice and healthy individuals. In our studies, lipid accumulation in DCs was caused by increased uptake of extracellular lipids due to upregulation of scavenger receptor A. DCs with high lipid content were not able to effectively stimulate allogeneic T cells or present tumor-associated antigens. DCs with high and normal lipid levels did not differ in expression of major histocompatibility complex and co-stimulatory molecules. However, lipid-laden DCs had a reduced capacity to process antigens. Pharmacological normalization of lipid abundance in DCs with an inhibitor of acetyl-CoA carboxylase restored the functional activity of DCs and substantially enhanced the effects of cancer vaccines. These findings suggest that immune responses in cancer can be improved by manipulating the lipid levels in DCs.

NO2 inhalation induces maturation of pulmonary CD11c+ cells that promote antigenspecific CD4+ T cell polarization

BACKGROUND

Nitrogen dioxide (NO2) is an air pollutant associated with poor respiratory health, asthma exacerbation, and an increased likelihood of inhalational allergies. NO2 is also produced endogenously in the lung during acute inflammatory responses. NO2 can function as an adjuvant, allowing for allergic sensitization to an innocuous inhaled antigen and the generation of an antigen-specific Th2 immune response manifesting in an allergic asthma phenotype. As CD11c+ antigen presenting cells are considered critical for naïve T cell activation, we investigated the role of CD11c+ cells in NO2-promoted allergic sensitization.

METHODS

We systemically depleted CD11c+ cells from transgenic mice expressing a simian diphtheria toxin (DT) receptor under of control of the CD11c promoter by administration of DT. Mice were then exposed to 15 ppm NO2 followed by aerosolized ovalbumin to promote allergic sensitization to ovalbumin and were studied after subsequent inhaled ovalbumin challenges for manifestation of allergic airway disease. In addition, pulmonary CD11c+ cells from wildtype mice were studied after exposure to NO2 and ovalbumin for cellular phenotype by flow cytometry and in vitro cytokine production.

RESULTS

Transient depletion of CD11c+ cells during sensitization attenuated airway eosinophilia during allergen challenge and reduced Th2 and Th17 cytokine production. Lung CD11c+ cells from wildtype mice exhibited a significant increase in MHCII, CD40, and OX40L expression 2 hours following NO2 exposure. By 48 hours, CD11c+MHCII+ DCs within the mediastinal lymph node (MLN) expressed maturation markers, including CD80, CD86, and OX40L. CD11c+CD11b- and CD11c+CD11b+ pulmonary cells exposed to NO2 in vivo increased uptake of antigen 2 hours post exposure, with increased ova-Alexa 647+ CD11c+MHCII+ DCs present in MLN from NO2-exposed mice by 48 hours. Co-cultures of ova-specific CD4+ T cells from naïve mice and CD11c+ pulmonary cells from NO2-exposed mice produced IL-1, IL-12p70, and IL-6 in vitro and augmented antigen-induced IL-5 production.

CONCLUSIONS

CD11c+ cells are critical for NO2-promoted allergic sensitization. NO2 exposure causes pulmonary CD11c+ cells to acquire a phenotype capable of increased antigen uptake, migration to the draining lymph node, expression of MHCII and co-stimulatory molecules required to activate naïve T cells, and secretion of polarizing cytokines to shape a Th2/Th17 response.

Approach towards optimal physiological T-cell-mediated immune response

Evaluation of: Kirak O, Frickel EV, Grotenbreg GM et al.: Transnuclear mice with predefined T cell receptor specificities against Toxoplasma gondii obtained via SCNT. Science 238, 243–248 (2010). Transgenic mice with defined T-cell receptor (TCR) specificity are useful for studying the involvement of T-cell-mediated immune responses to antigenic epitopes. However, these transgenic mice were not easily established. Their creation is time consuming due to several hindrances such as random integration of the α- and β-chains of the transgenic TCR and the presence of exogenous promoter, among others. These drawbacks explain why only a few TCR transgenic mice are available so far. Somatic cell nuclear transfer represents another means to generate mice with defined TCR specificity. Kirak et al. described an experimental model based on somatic cell nuclear transfer that allowed them to obtain mice harboring TCR specific to Toxoplasma gondii. The apparent ease in establishing this experimental model could lead to the generation of mice with defined T-cell immune responses against other antigens in the near future.

Tumor antigen epitopes interpreted by the immune system as self or abnormal-self differentially affect cancer vaccine responses

Epitope selection is an important consideration in the design of cancer vaccines, but factors affecting selection are not fully understood. We compared the immune responses to peptides and glycopeptides from the common human tumor antigen MUC1, a mucin that is coated with O-linked carbohydrates in its variable number of tandem repeats (VNTR) region. MUC1 expressed on tumor cells is characteristically underglycosylated, creating peptide and glycopeptide neoepitopes that are recognized by the immune system. The response to VNTR peptides is weaker in MUC1-transgenic mice (MUC1-Tg mice) than in wild-type (WT) mice, whereas the response to VNTR glycopeptides is equally strong in the two strains. Thus, glycopeptides seem to be recognized as foreign, whereas peptides, although immunogenic, are perceived as self. To explore this further, we generated MUC1 peptide- and glycopeptide-specific T-cell receptor transgenic mice and studied the function of their CD4 T cells when adoptively transferred into MUC1-Tg or WT mice. Peptide-specific T-cell precursors were not centrally deleted in MUC1-Tg mice and did not acquire a T regulatory phenotype. However, their response to the cognate peptide was reduced in MUC1-Tg mice compared with WT mice. In contrast, glycopeptide-specific CD4 T cells responded equally well in the two hosts and, when simultaneously activated, also enhanced the peptide-specific T-cell responses. Our data show that the immune system differentially recognizes various epitopes of tumor-associated antigens either as self or as foreign, and this controls the strength of antitumor immunity. This represents an important consideration for designing safe and effective cancer vaccines.

Immune activation induces immortalization of HTLV-1 LTR-Tax transgenic CD4+ T cells

Infection with the human T-cell leukemia virus-1 (HTLV-1) results in a variety of diseases including adult T-cell leukemia/lymphoma (ATL). Although the pathogenesis of these disorders is poorly understood, it involves complex interactions with the host immune system. Activation of infected T cells may play an important role in disease pathogenesis through induction of the oncogenic HTLV-1 Tax transactivator protein. To test this hypothesis, we employed transgenic mice in which Tax is regulated by the HTLV-1 LTR. T-cell receptor stimulation of LTR-Tax CD4(+) T cells induced Tax expression, hyper-proliferation, and immortalization in culture. The transition to cellular immortalization was accompanied by markedly increased expression of the antiapoptotic gene, mcl-1, previously implicated as important in T-cell survival. Immortalized cells exhibited a CD4(+)CD25(+)CD3(-) phenotype commonly observed in ATL. Engraftment of activated LTR-Tax CD4(+) T cells into NOD/Shi-scid/IL-2Rγ null mice resulted in a leukemia-like phenotype with expansion and tissue infiltration of Tax(+), CD4(+) lymphocytes. We suggest that immune activation of infected CD4(+) T cells plays an important role in the induction of Tax expression, T-cell proliferation, and pathogenesis of ATL in HTLV-1-infected individuals.

Blood-stage Plasmodium berghei infection leads to short-lived parasite-associated antigen presentation by dendritic cells

Despite extensive evidence that Plasmodium species are capable of stimulating the immune system, the association of malaria with a higher incidence of other infectious diseases and reduced responses to vaccination against unrelated pathogens suggests the existence of immune suppression. Recently, we provided evidence that blood-stage Plasmodium berghei infection leads to suppression of MHC class I-restricted immunity to third party (non-malarial) antigens as a consequence of systemic DC activation. This earlier study did not, however, determine whether reactivity was also impaired to MHC class II-restricted third party antigens or to Plasmodium antigens themselves. Here, we show that while P. berghei-expressed antigens were presented early in infection, there was a rapid decline in presentation within 4 days, paralleling impairment in MHC class I- and II-restricted presentation of third party antigens. This provides important evidence that P. berghei not only causes immunosuppression to subsequently encountered third party antigens, but also rapidly limits the capacity to generate effective parasite-specific immunity.

Semaphorins guide the entry of dendritic cells into the lymphatics by activating myosin II

The recirculation of leukocytes is essential for proper immune responses. However, the molecular mechanisms that regulate the entry of leukocytes into the lymphatics remain unclear. Here we show that plexin-A1, a principal receptor component for class III and class VI semaphorins, was crucially involved in the entry of dendritic cells (DCs) into the lymphatics. Additionally, we show that the semaphorin Sema3A, but not Sema6C or Sema6D, was required for DC transmigration and that Sema3A produced by the lymphatics promoted actomyosin contraction at the trailing edge of migrating DCs. Our findings not only demonstrate that semaphorin signals are involved in DC trafficking but also identify a previously unknown mechanism that induces actomyosin contraction as these cells pass through narrow gaps.

Transforming growth factor beta and CD25 are important for controlling systemic dissemination following Yersinia enterocolitica infection of the gut

Infection of the gut by invasive bacterial pathogens leads to robust inflammatory responses that if left unchecked can lead to autoimmune disease and other sequelae. How the immune system controls inflammation and limits collateral damage to the host during acute bacterial infection is poorly understood. Here, we report that antibody-mediated neutralization of transforming growth factor beta (TGF-beta) prior to infection with the model enteric pathogen Yersinia enterocolitica reduces the mean time to death by 1 day (P=0.001), leads to rapid colonization of the liver and lung, and is associated with exacerbation of inflammatory histopathology. During Yersinia enterocolitica infection CD4+ cells are the source of de novo TGF-beta transcription in the Peyer's patches, mesenteric lymph nodes, and spleen. Correspondingly there is both antigen-specific and -independent expansion of CD4+ CD25+ Foxp3+ and TGF-beta+ T-regulatory cells (T-regs) after Yersinia infection that is reduced in ovalbumin T-cell receptor-restricted OT-II mice. Functional inactivation of CD25 by anti-CD25 treatment results in more rapid death, dissemination of the bacteria to the liver and lungs, and exacerbated inflammatory histopathology, similar to what is seen during TGF-beta neutralization. Altogether, these data suggest that TGF-beta produced by T-regs is important in restricting bacteria during the acute phase of invasive bacterial infection of the gut. These data expand the roles of T-regs to include tempering inflammation during acute infection in addition to the well-established roles of T-regs in chronic infection, control of immune homeostasis, and autoimmune disease.

Recent advancements in cytotoxic T lymphocyte generation methods using carbohydrate-coated liposomes

Both tumor-specific CD4⁺ and CD8⁺ T cells have been identified, and the latter is known as a major effector of adaptive antitumor immune responses. Optimal antitumor immune responses are considered to require the concomitant activation of both CD8⁺ and CD4⁺ T cells and the additional selective activation of CD4⁺ T cells with helper, but not regulatory function. As optimal antitumor immune responses are generated by the concomitant activation of both T cell types, it is necessary for vaccine methods involving cytotoxic T-lymphocytes (CTLs) generation to possess a mechanism whereby antigen presenting cells can present administrated exogenous antigens on not only Major histocompatibility complex (MHC) class II, but also MHC class I molecules.

Differential subcellular localization of the regulatory T-cell protein LAG-3 and the coreceptor CD4

CD4 binds to MHC class II molecules and enhances T-cell activation. The CD4-related transmembrane protein LAG-3 (lymphocyte activation gene-3, CD223) binds to the same ligand but inhibits T-cell proliferation. We have previously shown that LAG-3 cell surface expression is tightly regulated by extracellular cleavage in order to regulate its potent inhibitory activity. Given this observation and the contrasting functions of CD4 and LAG-3, we investigated the cell distribution, location and transport of these related cell surface molecules. As expected, the vast majority of CD4 is expressed at the cell surface with minimal intracellular localization, as determined by flow cytometry, immunoblotting and confocal microscopy. In contrast, nearly half the cellular content of LAG-3 is retained in intracellular compartments. This significant intracellular storage of LAG-3 appears to facilitate its rapid translocation to the cell surface following T-cell activation, which was much faster for LAG-3 than CD4. Increased vesicular pH inhibited translocation of both CD4 and LAG-3 to the plasma membrane. While some colocalization of the microtubule organizing center, early/recycling endosomes and secretory lysosomes was observed with CD4, significantly greater colocalization was observed with LAG-3. Analysis of CD4:LAG-3 chimeras suggested that multiple domains may contribute to intracellular retention of LAG-3. Thus, in contrast with CD4, the substantial intracellular storage of LAG-3 and its close association with the microtubule organizing center and recycling endosomes may facilitate its rapid translocation to the cell surface during T-cell activation and help to mitigate T-cell activation.

Fusion proteins for versatile antigen targeting to cell surface receptors reveal differential capacity to prime immune responses

Targeting of proteins to APCs is an attractive strategy for eliciting adaptive immune responses. However, the relationship between the choice of the targeted receptor and the quality and quantity of responses remains poorly understood. We describe a strategy for expression of Ags including hydrophobic proteins as soluble fusion proteins that are optimized for proteasome-dependent MHC class I-restricted cross-presentation and form stable complexes with a wide variety of targeting Abs. Upon s.c. immunization, these complexes were initially taken up by CD169+ lymph node subcapsular sinus macrophages. In the OVA model system, receptor-targeted antigenic complexes primed specific T and B cell responses in vitro and in vivo at least 100-fold more efficiently than Ag alone. Comparison of 10 targeting receptors allowed us to establish a ranking with respect to priming of CD8+ T cell responses and demonstrated striking differences with respect to the relative efficacy of CD8+ and CD4+ T cell subset and B cell priming. The described fusion proteins should help in developing optimized strategies for targeted delivery of protein Ags in the context of tolerization or vaccination.

Identification of a novel antigen cross-presenting cell type in spleen

Antigen-presenting cells (APC), like dendritic cells (DC), are essential for T-cell activation, leading to immunity or tolerance. Multiple DC subsets each play a unique role in the immune response. Here, a novel splenic dendritic-like APC has been characterized in mice that has immune function and cell surface phenotype distinct from other, described DC subsets. These were identified as a cell type continuously produced in spleen long-term cultures (LTC) and have an in vivo equivalent cell type in mice, namely 'L-DC'. This study characterizes LTC-DC in terms of marker phenotype and function, and compares them with L-DC and other known splenic DC and myeloid subsets. L-DC display a myeloid dendritic-like phenotype equivalent to LTC-DC as CD11c(lo) CD11b(hi) MHC-II(-) CD8α(-) cells, distinct by high accessibility and endocytic capacity for blood-borne antigen. Both LTC-DC and L-DC have strong antigen cross-presentation ability leading to strong activation of CD8(+) T cells, particularly after exposure to lipopolysaccharide. However, they have weak ability to stimulate CD4(+) T cells in antigen-specific responses. Evidence is presented here for a novel DC type produced by in vitro haematopoiesis which has distinct antigen-presenting potential and reflects a DC subset present also in vivo in spleen.

A spread-deficient cytomegalovirus for assessment of first-target cells in vaccination

Human cytomegalovirus (HCMV) is a human pathogen that causes severe disease primarily in the immunocompromised or immunologically immature individual. To date, no vaccine is available. We describe use of a spread-deficient murine CMV (MCMV) as a novel approach for betaherpesvirus vaccination. To generate a spread-deficient MCMV, the conserved, essential gene M94 was deleted. Immunization with MCMV-DeltaM94 is apathogenic and protective against wild-type challenge even in highly susceptible IFNalphabetaR(-/-) mice. MCMV-DeltaM94 was able to induce a robust CD4(+) and CD8(+) T-cell response as well as a neutralizing antibody response comparable to that induced by wild-type infection. Endothelial cells were identified as activators of CD8(+) T cells in vivo. Thus, the vaccination with a spread-deficient betaherpesvirus is a safe and protective strategy and allows the linkage between cell tropism and immunogenicity. Furthermore, genomes of MCMV-DeltaM94 were present in lungs 12 months after infection, revealing first-target cells as sites of genome maintenance.

On the composition of the preimmune repertoire of T cells specific for Peptide-major histocompatibility complex ligands

Millions of T cells are produced in the thymus, each expressing a unique alpha/beta T cell receptor (TCR) capable of binding to a foreign peptide in the binding groove of a host major histocompatibility complex (MHC) molecule. T cell-mediated immunity to infection is due to the proliferation and differentiation of rare clones in the preimmune repertoire that by chance express TCRs specific for peptide-MHC (pMHC) ligands derived from the microorganism. Here we review recent findings that have altered our understanding of how the preimmune repertoire is established. Recent structural studies indicate that a germline-encoded tendency of TCRs to bind MHC molecules contributes to the MHC bias of T cell repertoires. It has also become clear that the preimmune repertoire contains functionally heterogeneous subsets including recent thymic emigrants, mature naive phenotype cells, memory phenotype cells, and natural regulatory T cells. In addition, sensitive new detection methods have revealed that the repertoire of naive phenotype T cells consists of distinct pMHC-specific populations that consistently vary in size in different individuals. The implications of these new findings for the clonal selection theory, self-tolerance, and immunodominance are discussed.

Early detrimental T-cell effects in experimental cerebral ischemia are neither related to adaptive immunity nor thrombus formation

T cells contribute to the pathophysiology of ischemic stroke by yet unknown mechanisms. Mice with transgenic T-cell receptors (TCRs) and mutations in costimulatory molecules were used to define the minimal immunologic requirements for T cell–mediated ischemic brain damage. Stroke was induced in recombination activating gene 1–deficient (RAG1−/−) mice devoid of T and B cells, RAG1−/− mice reconstituted with B cells or T cells, TCR-transgenic mice bearing 1 single CD8+ (2C/RAG2, OTI/RAG1 mice) or CD4+ (OTII/RAG1, 2D2/RAG1 mice) TCR, mice lacking accessory molecules of TCR stimulation (CD28−/−, PD1−/−, B7-H1−/− mice), or mice deficient in nonclassical T cells (natural killer T [NKT] and γδ T cells) by transient middle cerebral artery occlusion (tMCAO). Stroke outcome was assessed at day 1. RAG1−/− mice and RAG1−/− mice reconstituted with B cells developed significantly smaller brain infarctions compared with controls, but thrombus formation after FeCl3-induced vessel injury was unimpaired. In contrast, TCR-transgenic mice and mice lacking costimulatory TCR signals were fully susceptible to tMCAO similar to mice lacking NKT and γδ T cells. These findings were corroborated by adoptive transfer experiments. Our data demonstrate that T cells critically contribute to cerebral ischemia, but their detrimental effect neither depends on antigen recognition nor TCR costimulation or thrombus formation.

The zinc-finger protein MAZR is part of the transcription factor network that controls the CD4 versus CD8 lineage fate of double-positive thymocytes

The CD4 versus CD8 lineage specification of thymocytes is linked to coreceptor expression. The transcription factor MAZR has been identified as an important regulator of Cd8 expression. Here we show that variegated CD8 expression by loss of Cd8 enhancers was reverted in MAZR-deficient mice, which confirms that MAZR negatively regulates the Cd8 loci during the transition to the double-positive (DP) stage. Moreover, loss of MAZR led to partial redirection of major histocompatibility complex (MHC) class I-restricted thymocytes into CD4(+) helper-like T cells, which correlated with derepression of Th-POK, a central transcription factor for helper-lineage development. MAZR bound the silencer of the gene encoding Th-POK, which indicated direct regulation of this locus by MAZR. Thus, MAZR is part of the transcription factor network that regulates the CD8 lineage differentiation of DP thymocytes.

Echinacea purpurea extracts modulate murine dendritic cell fate and function

Echinacea is a top-selling herbal remedy that purportedly acts as an immunostimulant. However, the specific immunomodulatory effects of Echinacea remain to be elucidated. We focused on defining the effects of Echinacea purpurea extracts in dendritic cells (DCs), which generate innate and adaptive immune responses. We hypothesized that E. purpurea extracts would enhance murine bone marrow-derived DC (BMDC) activation leading to increased immune responses. The fate and function of DCs from C57Bl/6 mice was evaluated following 48h exposure to E. purpurea root and leaf extracts. Flow cytometry revealed that the polysaccharide-rich root extract increased the expression of MHC class II, CD86, and CD54 surface biomarkers whereas the alkylamide-rich leaf extract inhibited expression of these molecules. Production of IL-6 and TNF-alpha increased in a concentration-dependent manner with exposure to the root, but not leaf, extract. In contrast, the leaf but not root extract inhibited the enzymatic activity of cyclooxygenase-2. While both extracts decreased the uptake of ovalbumin by BMDCs, the leaf but not root extract inhibited the antigen-specific activation of naïve CD4(+) T cells from OT II/Thy1.1 mice. Collectively, these results suggest that E. purpurea can be immunostimulatory, immunosuppressive, and/or anti-inflammatory depending on the portion of the plant and extraction method.

Blood fluke exploitation of non-cognate CD4+ T cell help to facilitate parasite development

Schistosoma blood flukes, which infect over 200 million people globally, co-opt CD4+ T cell-dependent mechanisms to facilitate parasite development and egg excretion. The latter requires Th2 responses, while the mechanism underpinning the former has remained obscure. Using mice that are either defective in T cell receptor (TCR) signaling or that lack TCRs that can respond to schistosomes, we show that naïve CD4+ T cells facilitate schistosome development in the absence of T cell receptor signaling. Concurrently, the presence of naïve CD4+ T cells correlates with both steady-state changes in the expression of genes that are critical for the development of monocytes and macrophages and with significant changes in the composition of peripheral mononuclear phagocyte populations. Finally, we show that direct stimulation of the mononuclear phagocyte system restores blood fluke development in the absence of CD4+ T cells. Thus we conclude that schistosomes co-opt innate immune signals to facilitate their development and that the role of CD4+ T cells in this process may be limited to the provision of non-cognate help for mononuclear phagocyte function. Our findings have significance for understanding interactions between schistosomiasis and other co-infections, such as bacterial infections and human immunodeficiency virus infection, which potently stimulate innate responses or interfere with T cell help, respectively. An understanding of immunological factors that either promote or inhibit schistosome development may be valuable in guiding the development of efficacious new therapies and vaccines for schistosomiasis.

Transnuclear mice with predefined T cell receptor specificities against Toxoplasma gondii obtained via SCNT

Mice that are transgenic for rearranged antigen-specific T cell receptors (TCRs) are essential tools to study T cell development and function. Such TCRs are usually isolated from the relevant T cells after long-term culture, often after repeated antigen stimulation, which unavoidably skews the T cell population used. Random genomic integration of the TCR alpha and beta chain and expression from nonendogenous promoters represent additional drawbacks of transgenics. Using epigenetic reprogramming via somatic cell nuclear transfer, we demonstrated that T cells with predefined specificities against Toxoplasma gondii can be used to generate mouse models that express the TCR from their endogenous loci, without experimentally introduced genetic modification. The relative ease and speed with which such transnuclear models can be obtained holds promise for the construction of other disease models.

Identification of a unique population of tissue-memory CD4+ T cells in the airways after influenza infection that is dependent on the integrin VLA-1

During the immune response to influenza infection, activated T cells are distributed to both lymphoid and extralymphoid tissues, including the infected airways where direct recognition of viral Ag-bearing cells takes place. The collagen-binding alpha(1)beta(1) integrin VLA-1 is essential for the development of memory CD8(+) T cells in the airways, and although expressed by some CD4(+) T cells, its significance has not been demonstrated. We investigated the role of VLA-1 on virus-specific CD4(+) T cells during and after primary or secondary influenza infection of mice. The proportion of CD4(+) cells expressing CD49a (alpha(1) integrin) was low in all tissues sampled during primary infection but increased in the airways after viral clearance. Furthermore, during the first 24 h of a secondary influenza challenge, the majority of IFN-gamma-secreting effector CD4(+) T cells from the airways was in the CD49a(+) population. Airway CD49a(+)CD4(+) cells also expressed reduced markers of apoptosis compared with CD49a(-) cells, and fewer memory or effector CD4(+) cells could be recovered from airways of alpha(1)(-/-) mice, although lymphoid tissues appeared unaffected. These data suggest VLA-1 expression defines a population of tissue memory CD4(+) T cells that act as rapid effectors upon reinfection, and VLA-1 expression is integral to their accumulation in the airways.

B cells are required for optimal CD4+ and CD8+ T cell tumor immunity: therapeutic B cell depletion enhances B16 melanoma growth in mice

B lymphocytes can both positively and negatively regulate cellular immune responses. Previous studies have demonstrated augmented T cell-mediated tumor immunity in genetically B cell-deficient mice, suggesting that therapeutic B cell depletion would enhance tumor immunity. To test this hypothesis and quantify B cell contributions to T cell-mediated anti-tumor immune responses, mature B cells were depleted from wild-type adult mice using CD20 mAb prior to syngeneic B16 melanoma tumor transfers. Remarkably, s.c. tumor volume and lung metastasis were increased 2-fold in B cell-depleted mice. Effector-memory and IFN-gamma-or TNF-alpha-secreting CD4(+) and CD8(+) T cell induction was significantly impaired in B cell-depleted mice with tumors. Tumor Ag-specific CD8(+) T cell proliferation was also impaired in tumor-bearing mice that lacked B cells. Thus, B cells were required for optimal T cell activation and cellular immunity in this in vivo nonlymphoid tumor model. Although B cells may not have direct effector roles in tumor immunity, impaired T cell activation, and enhanced tumor growth in the absence of B cells argue against previous proposals to augment tumor immunity through B cell depletion. Rather, targeting tumor Ags to B cells in addition to dendritic cells is likely to optimize tumor-directed vaccines and immunotherapies.

Gamma interferon produced by antigen-specific CD4+ T cells regulates the mucosal immune responses to Citrobacter rodentium infection

Citrobacter rodentium, a murine model pathogen for enteropathogenic Escherichia coli, colonizes the surface of intestinal epithelial cells and causes mucosal inflammation. This bacterium is an ideal model for investigating pathogen-host immune interactions in the gut. It is well known that gene transcripts for Th1 cytokines are highly induced in colonic tissue from mice infected with C. rodentium. However, it remains to be seen whether the Th1 or Th2 cytokines produced by antigen-specific CD4(+) T cells provide effective regulation of the host immune defense against C. rodentium infection. To investigate the antigen-specific immune responses, C. rodentium expressing ovalbumin (OVA-C. rodentium), a model antigen, was generated and used to define antigen-specific responses under gamma interferon (IFN-gamma)-deficient or interleukin-4 (IL-4)-deficient conditions in vivo. The activation of antigen-specific CD4(+) T cells and macrophage phagocytosis were evaluated in the presence of IFN-gamma or IL-4 in vitro. IFN-gamma-deficient mice exhibited a loss of body weight and a higher bacterial concentration in feces during OVA-C. rodentium infection than C57BL/6 (wild type) or IL-4-deficient mice. This occurred through the decreased efficiency of macrophage phagocytosis and the activation of antigen-specific CD4(+) T cells. Furthermore, a deficiency in antigen-specific CD4(+) T-cell-expressed IFN-gamma led to a higher susceptibility to mucosal and gut-derived systemic OVA-C. rodentium infection. These results show that the IFN-gamma produced by antigen-specific CD4(+) T cells plays an important role in the defense against C. rodentium.

CD45-Csk phosphatase-kinase titration uncouples basal and inducible T cell receptor signaling during thymic development

The kinase-phosphatase pair Csk and CD45 reciprocally regulate phosphorylation of the inhibitory tyrosine of the Src family kinases Lck and Fyn. T cell receptor (TCR) signaling and thymic development require CD45 expression but proceed constitutively in the absence of Csk. Here, we show that relative titration of CD45 and Csk expression reveals distinct regulation of basal and inducible TCR signaling during thymic development. Low CD45 expression is sufficient to rescue inducible TCR signaling and positive selection, whereas high expression is required to reconstitute basal TCR signaling and beta selection. CD45 has a dual positive and negative regulatory role during inducible but not basal TCR signaling. By contrast, Csk titration regulates basal but not inducible signaling. High physiologic expression of CD45 is thus required for two reasons-to downmodulate inducible TCR signaling during positive selection and to counteract Csk during basal TCR signaling.

Lck mediates Th2 differentiation through effects on T-bet and GATA-3

The Src family kinase Lck has been shown to be crucial in T cell signaling and development. However, its role in Th effector functions is not well understood. Lck has previously been shown to play a role in the cytokine expression of Th2 cells, but the mechanism by which Lck influences Th2 effector functions is unknown. Using a mouse model, we report that Lck is important in regulating the expression of IL-4 in Th2 skewed cells but is not as necessary for the expression of Th2 cytokines IL-5, IL-10, and IL-13. Furthermore, in the absence of Lck, T-bet and GATA-3 expression is aberrant. Moreover, this atypical expression pattern of T-bet and GATA-3 correlates with increased histone 3 acetylation at the Ifng locus and production of the Th1 cytokine IFN-gamma. We find overexpression of GATA-3 restores IL-4 expression in lck(-/-) Th2 cells; this indicates that the decreased IL-4 expression is due in part to reduced amounts of GATA-3. Taken together, these data imply that Lck mediates Th2 differentiation through effects on T-bet and GATA-3.

Inhibition of antigen presentation and T cell costimulation blocks PTH-induced bone loss

T cells are required for continuous parathyroid hormone (cPTH) treatment to induce bone loss as they sensitize stromal cells to PTH through CD40 ligand (CD40L), a surface molecule of activated T cells. Since CD40L expression is a feature of activated T cells, we investigated whether antigen (Ag)-mediated T cell activation is required for PTH to exert its catabolic activity. We report that inhibition of Ag presentation through silencing of either class I or class II MHC-T cell receptor (TCR) interaction prevents the cortical bone loss induced by in vivo cPTH treatment. We also show that the bone loss and the stimulation of bone resorption induced by cPTH treatment are prevented by CTLA4-Ig, an inhibitor of T cell costimulation approved for the treatment of rheumatoid arthritis. Since inhibition of antigen-driven T cell activation by blockade of either TCR signaling or T cell costimulation is sufficient to silence the catabolic activity of cPTH, antigen-presenting cells and T lymphocyte interactions therefore play a critical role in the mechanism of action of PTH.

Unaltered negative selection and Treg development of self-reactive thymocytes in TCR transgenic Fyn-deficient mice

The tyrosine kinase Fyn has been implicated as playing an important role in the generation of both stimulatory and inhibitory signaling events induced by TCR engagement. To assess the role of Fyn for antigen-driven negative selection and Treg development, which are both dependent on the strength and nature of TCR signaling, we generated mice that co-express the transgenes for OVA and the OT-II TCR, which recognizes a peptide from OVA. In mice expressing both transgenes, negative selection, Treg development in the thymus, and the number of Treg in the periphery were each unaffected by ablation of Fyn. Moreover, fyn(-/-) Treg were functional, as assessed in vitro. We further tested the role of Fyn for the adaptor function of c-Cbl, using mice containing a point mutation in c-Cbl that abolishes its E3 ubiquitin ligase function but maintains its adaptor function. The functional and signaling properties of this mutant c-Cbl were unaltered in fyn(-/-) thymocytes. Combined, these data indicate that Fyn was not required for the induction of central tolerance by negative selection, the adaptor protein role of c-Cbl, or the normal development and function of Treg.

Epidermal gammadelta T cells sense precancerous cellular dysregulation and initiate immune responses

Hyperplasia associated with a loss of tissue homeostasis can induce DNA replication stress, leading to precancerous dysregulation. Epidermal gammadelta T cells reside in the primary barrier that protects against diverse environmental insults; however, the functions of these T cells in tissue surveillance are not completely understood. In mice with inducible Notch1 inactivation in keratinocytes that causes epidermal hyperplasia, epidermal gammadelta T cells sensed stressed keratinocytes and migrated into the cutaneous draining lymph nodes. Simultaneous induction of beta-galactosidase (beta-Gal) as a putative antigen expressed in the process of precancerous dysregulation and Notch1 ablation in the epidermis resulted in elevated beta-Gal-specific IgG2a production. Epidermal gammadelta T cells were found to have the capacity to express chemokine (C-C motif) receptor 7 and migrate into the lymph nodes. Cutaneous draining lymph node cells in Notch1-inactivated mice expressed high levels of IFN-gamma upon anti-CD3 plus anti-CD28 stimulation. Furthermore, induced expression of beta-Gal in mice that lacked epidermal gammadelta T cells failed to induce anti-beta-Gal IgG. These results suggest that epidermal gammadelta T cells play an essential role in the initiation process of epidermal antigen-specific humoral immune responses and demonstrate the importance of epidermal gammadelta T cells in sensing precancerous dysregulation and activating adaptive immunity.

Comparison of chitosan nanoparticles and chitosan hydrogels for vaccine delivery

In this work the potential of chitosan nanoparticles (CNP) and thermosensitive chitosan hydrogels as particulate and sustained release vaccine delivery systems was investigated. CNP and chitosan hydrogels were prepared, loaded with the model protein antigen ovalbumin (OVA) and characterised. The immunostimulatory capacity of these vaccine delivery systems was assessed in-vitro and in-vivo. Particle sizing measurements and SEM images showed that optimised OVA-loaded CNP had a size of approximately 200 nm, a polydispersity index < 0.2, and a positive zeta-potential of approximately 18 mV. The amount of OVA adsorbed onto CNP was high with an adsorption efficacy of greater than 96%. Raman spectroscopy indicated conformational changes of OVA when adsorbed onto the surface of CNP. Uptake of the dispersions and immunological activation of murine dendritic cells in-vitro could be demonstrated. Investigation of the release of fluorescently-labelled OVA (FITC-OVA) from CNP and chitosan hydrogels in-vitro showed that approximately 50% of the total protein was released from CNP within a period of ten days; release of antigen from chitosan gel occurred in a more sustained manner, with < 10% of total protein being released after 10 days. The slow release from gel formulations may be explained by the strong interactions of the protein with chitosan. While OVA-loaded CNP showed no significant immunogenicity, formulations of OVA in chitosan gel were able to stimulate both cell-mediated and humoral immunity in-vivo.

TLR2 engagement on dendritic cells promotes high frequency effector and memory CD4 T cell responses

Ligation of TLR by distinct pathogen components provides essential signals for T cell priming, although how individual TLR engagement affects primary and memory T cell responses is not well defined. In this study, we demonstrate distinct effects of TLR2 vs TLR4 engagement on primary and memory CD4 T cell responses due to differential effects on APC. Priming of influenza hemagglutinin (HA)-specific naive CD4 T cells with HA peptide and the TLR2 agonist Pam3CysK in vivo resulted in a high frequency of activated HA-specific CD4 T cells that predominantly produced IL-2 and IL-17, whereas priming with HA peptide and the TLR4 agonist LPS yielded a lower frequency of HA-specific CD4 T cells and predominant IFN-gamma producers. TLR2 agonist priming depended on TLR2 expression by APC, as wild-type CD4 T cells did not expand in response to peptide and Pam3CysK in TLR2-deficient hosts. TLR2-mediated priming also led to an increased frequency of Ag-specific memory CD4 T cells compared with TLR4 priming and mediated enhanced secondary responses to influenza challenge. Our results show that TLR engagement on APC influences both primary and secondary CD4 T cell responses, and suggest that long-term functional capacities of T cells are set by innate signals during early phases of an infection.

New design of MHC class II tetramers to accommodate fundamental principles of antigen presentation

Direct identification and isolation of Ag-specific T cells became possible with the development of MHC tetramers, based on fluorescent avidins displaying biotinylated peptide-MHC complexes. This approach, extensively used for MHC class I-restricted T cells, has met very limited success with class II peptide-MHC complex tetramers (pMHCT-2) for the detection of CD4(+)-specific T cells. In addition, a very large number of these reagents, although capable of specifically activating T cells after being coated on solid support, is still unable to stain. To try to understand this puzzle and design usable tetramers, we examined each parameter critical for the production of pMHCT-2 using the I-A(d)-OVA system as a model. Through this process, the geometry of peptide-MHC display by avidin tetramers was examined, as well as the stability of rMHC molecules. However, we discovered that the most important factor limiting the reactivity of pMHCT-2 was the display of peptides. Indeed, long peptides, as presented by MHC class II molecules, can be bound to I-A/HLA-DQ molecules in more than one register, as suggested by structural studies. This mode of anchorless peptide binding allows the selection of a broader repertoire on single peptides and should favor anti-infectious immune responses. Thus, beyond the technical improvements that we propose, the redesign of pMHCT-2 will give us the tools to evaluate the real size of the CD4 T cell repertoire and help us in the production and testing of new vaccines.

Langerin+ CD8alpha+ dendritic cells are critical for cross-priming and IL-12 production in response to systemic antigens

Distinct dendritic cell (DC) subsets differ with respect to pathways of Ag uptake and intracellular routing to MHC class I or MHC class II molecules. Murine studies suggest a specialized role for CD8alpha(+) DC in cross-presentation, where exogenous Ags are presented on MHC class I molecules to CD8(+) T cells, while CD8alpha(-) DC are more likely to present extracellular Ags on MHC class II molecules to CD4(+) T cells. As a proportion of CD8alpha(+) DC have been shown to express langerin (CD207), we investigated the role of langerin(+)CD8alpha(+) DC in presenting Ag and priming T cell responses to soluble Ags. When splenic DC populations were sorted from animals administered protein i.v., the ability to cross-present Ag was restricted to the langerin(+) compartment of the CD8alpha(+) DC population. The langerin(+)CD8alpha(+) DC population was also susceptible to depletion following administration of cytochrome c, which is known to trigger apoptosis if diverted to the cytosol. Cross-priming of CTL in the presence of the adjuvant activity of the TLR2 ligand N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-[R]-Cys-[S]-Serl-[S]-Lys4-trihydrochloride or the invariant NKT cell ligand alpha-galactosylceramide was severely impaired in animals selectively depleted of langerin(+) cells in vivo. The production of IL-12p40 in response to these systemic activation stimuli was restricted to langerin(+)CD8alpha(+) DC, and the release of IL-12p70 into the serum following invariant NKT cell activation was ablated in the absence of langerin(+) cells. These data suggest a critical role for the langerin(+) compartment of the CD8alpha(+) DC population in cross-priming and IL-12 production.

Antigen-specific CD4 cells assist CD8 T-effector cells in eliminating keratinocytes

Keratinocytes expressing tumor or viral antigens can be eliminated by antigen-primed CD8 cytotoxic T cells. CD4 T-helper cells help induction of CD8 cytotoxic T cells from naive precursors and generation of CD8 T-cell memory. In this study, we show, unexpectedly, that CD4 cells are also required to assist primed CD8 effector T cells in rejection of skin expressing human growth hormone, a neo-self-antigen, in keratinocytes. The requirement for CD4 cells can be substituted by CD40 costimulation. Rejection of skin expressing ovalbumin (OVA), a non-self-antigen, by primed CD8 cytotoxic T cells can in contrast occur without help from antigen-specific CD4 T cells. However, rejection of OVA expressing keratinocytes is helped by antigen-specific CD4 T cells if only low numbers of primed or naive OVA-specific CD8 T cells are available. Effective immunotherapy directed at antigens expressed in squamous cancer may therefore be facilitated by induction of tumor antigen-specific CD4 helper T cells, as well as cytotoxic CD8 T cells.

Conditioning of the injection site with CpG enhances the migration of adoptively transferred dendritic cells and endogenous CD8+ T-cell responses

The efficiency of immunotherapy using tumor-antigen-loaded dendritic cells (DCs) is severely limited by the impaired migration of injected cells from the application site to the draining lymph nodes. As described earlier, pretreatment of the injection site with inflammatory cytokines enhances DC migration. We wanted to test whether toll-like receptor (TLR) ligands can improve migration of murine bone marrow-derived DC (BMDC) and the subsequent T-cell responses. For this purpose, we established an experimental setup closely resembling human vaccination protocols that served to investigate DC migration from the skin to the draining lymph nodes. We observed that BMDC, matured with a cytokine cocktail (tumor necrosis factor-alpha, interleukin-beta, interleukin-6, prostaglandin E2), strongly expressed CCR7. The migration efficiency of adoptively transferred mature BMDCs was determined by the number of cells injected and the application site. We decided to inject DC intradermally into the ear skin and investigated the effects of pretreatment of the injection site with various TLR ligands. Conditioning of the skin site with the TLR ligands CpG and Peptidoglycan increased the number of DCs arriving in the lymph node. Mechanical stress applied to the skin, such as tape stripping of the skin was equally effective. Importantly, only pretreatment with CpG enhanced responses of endogenous CD8 T cells. Thus, conditioning of the injection site with the TLR ligand CpG could be a new promising way to improve the outcome of DC immunotherapy.

Color-coded real-time cellular imaging of lung T-lymphocyte accumulation and focus formation in a mouse asthma model

BACKGROUND

A critical role for CD4(+)T(H)2 cells in the pathogenesis of acute asthma has been demonstrated in the studies of human asthma as well as of animal models of asthma. T(H)2-cell migration into the lung is crucial for the initiation of asthma phenotype, but the dynamics of this process are poorly understood because it has been difficult to visualize this process.

OBJECTIVE

Our aim was to image the cellular dynamics of the migration of T(H)2 cells into the lung of living animals in a mouse model of asthma and identify the cellular processes required for the initiation of the asthma phenotype.

METHODS

We developed a color-coded real-time imaging model of cell migration into the lung using green fluorescent protein (GFP) and red fluorescent protein (RFP) transgenic CD4 T cells.

RESULTS

Selective accumulation of antigen-specific CD4 T cells in the lungs was quantitatively imaged in a mouse model of asthma. The inhibition of accumulation by dexamethasone was imaged. Accumulating GFP(+) T(H)2 cells formed foci in the lungs from 6 to 20 hours after antigen inhalation. This process was also inhibited by the administration of anti-intercellular adhesion molecule 1 or anti-vascular cell adhesion molecule 1 mAbs. Two days after inhalation of antigen, GFP(+) T(H)2 cells were detected in the area of eosinophil infiltration.

CONCLUSION

Focus formation generated by accumulating antigen-specific T(H)2 cells in the lung appeared to be a critical process in the initiation of the asthma phenotype. This new model enables the study of in vivo cell biology of airway inflammation and novel drug discovery for lung inflammatory diseases.

PD-1 signalling in CD4(+) T cells restrains their clonal expansion to an immunogenic stimulus, but is not critically required for peptide-induced tolerance

The ultimate outcome of T-cell recognition of peptide-major histocompatibility complex (MHC) complexes is determined by the molecular context in which antigen presentation is provided. The paradigm is that, after exposure to peptides presented by steady-state dendritic cells (DCs), inhibitory signals dominate, leading to the deletion and/or functional inactivation of antigen-reactive T cells. This has been utilized in a variety of models providing peptide antigen in soluble form in the absence of adjuvant. A co-inhibitory molecule of considerable current interest is PD-1. Here we show that there is the opportunity for the PD-1/PD-L1 interaction to function in inhibiting the T-cell response during tolerance induction. Using traceable CD4(+) T-cell receptor (TCR) transgenic cells, together with a blocking antibody to disrupt PD-1 signalling, we explored the roles of PD-1 in the induction of tolerance versus a productive immune response. Intact PD-1 signalling played a role in limiting the extent of CD4(+) T-cell accumulation in response to an immunogenic stimulus. However, PD-1 signalling was not required for either the induction, or the maintenance, of peptide-induced tolerance; a conclusion underlined by successful tolerance induction in TCR transgenic cells genetically deficient for PD-1. These observations contrast with the reported requirement for PD-1 signals in CD8(+) T-cell tolerance.