Cutting edge: intravenous soluble antigen is presented to CD4 T cells by CD8- dendritic cells, but cross-presented to CD8 T cells by CD8+ dendritic cells

Mouse spleen contains three distinct mature dendritic cell (DC) populations (CD4(+)8(-), CD4(-)8(-), and CD4(-)8(+)) which retain a capacity to take up particulate and soluble AGS: Although the three splenic DC subtypes showed similar uptake of injected soluble OVA, they differed markedly in their capacity to present this Ag and activate proliferation in OVA-specific CD4 or CD8 T cells. For class II MHC-restricted presentation to CD4 T cells, the CD8(-) DC subtypes were more efficient, but for class I MHC-restricted presentation to CD8 T cells, the CD8(+) DC subtype was far more effective. This differential persisted when the DC were activated with LPS. The CD8(+) DC are therefore specialized for in vivo cross-presentation of exogenous soluble Ags into the class I MHC presentation pathway.     

Inhibition of graft-versus-host disease by double-negative regulatory T cells

Pretransplant infusion of lymphocytes that express a single allogeneic MHC class I Ag has been shown to induce tolerance to skin and heart allografts that express the same alloantigens. In this study, we demonstrate that reconstitution of immunoincompetent mice with spleen cells from MHC class I L(d)-mismatched donors does not cause graft-vs-host disease (GVHD). Recipient mice become tolerant to skin allografts of lymphocyte donor origin while retaining immunity to third-party alloantigens. The mechanism involves donor-derived CD3(+)CD4(-)CD8(-) double-negative T regulatory (DN Treg) cells, which greatly increase and form the majority of T lymphocytes in the spleen of recipient mice. DN Treg cells isolated from tolerant recipient mice can suppress the proliferation of syngeneic antihost CD8(+) T cells in vitro. Furthermore, we demonstrate that DN Treg cells can be generated in vitro by stimulating them with MHC class I L(d)-mismatched lymphocytes. These in vitro generated L(d)-specific DN Treg cells are able to down-regulate the activity of antihost CD8(+) T cells in vitro by directly killing activated CD8(+) T cells. Moreover, infusing in vitro generated L(d)-mismatched DN Treg cells prevented the development of GVHD caused by allogeneic CD8(+) T cells. Together these data demonstrate that infusion of single MHC class I locus-mismatched lymphocytes may induce donor-specific transplantation tolerance through activation of DN Treg cells, which can suppress antihost CD8(+) T cells and prevent the development of GVHD. This finding indicates that using single class I locus-mismatched grafts may be a viable alternative to using fully matched grafts in bone marrow transplantation.     

A new dynamic model of CD8+ T effector cell responses via CD4+ T helper-antigen-presenting cells

A long-standing paradox in cellular immunology has been the conditional requirement for CD4(+) Th cells in priming of CD8(+) CTL responses. We propose a new dynamic model of CD4(+) Th cells in priming of Th-dependent CD8(+) CTL responses. We demonstrate that OT II CD4(+) T cells activated by OVA-pulsed dendritic cells (DC(OVA)) are Th1 phenotype. They acquire the immune synapse-composed MHC II/OVAII peptide complexes and costimulatory molecules (CD54 and CD80) as well as the bystander MHC class I/OVAI peptide complexes from the DC(OVA) by DC(OVA) stimulation and thus also the potential to act themselves as APCs. These CD4(+) Th-APCs stimulate naive OT I CD8(+) T cell proliferation through signal 1 (MHC I/OVAI/TCR) and signal 2 (e.g., CD54/LFA-1 and CD80/CD28) interactions and IL-2 help. In vivo, they stimulate CD8(+) T cell proliferation and differentiation into CTLs and induce effective OVA-specific antitumor immunity. Taken together, this study demonstrates that CD4(+) Th cells carrying acquired DC Ag-presenting machinery can, by themselves, efficiently stimulate CTL responses. These results have substantial implications for research in antitumor and other aspects of immunity.     

T cells signaled by NF-kappa B- dendritic cells are sensitized not anergic to subsequent activation

Paradoxically, while peripheral self-tolerance exists for constitutively presented somatic self Ag, self-peptide recognized in the context of MHC class II has been shown to sensitize T cells for subsequent activation. We have shown that MHC class II(+)CD86(+)CD40(-) DC, which can be generated from bone marrow in the presence of an NF-kappa B inhibitor, and which constitutively populate peripheral tissues and lymphoid organs in naive animals, can induce Ag-specific tolerance. In this study, we show that CD40(-) human monocyte-derived dendritic cells (DC), generated in the presence of an NF-kappa B inhibitor, signal phosphorylation of TCR zeta, but little proliferation or IFN-gamma in vitro. Proliferation is arrested in the G(1)/G(0) phase of the cell cycle. Surprisingly, responding T cells are neither anergic nor regulatory, but are sensitized for subsequent IFN-gamma production. The data indicate that signaling through NF-kappa B determines the capacity of DC to stimulate T cell proliferation. Functionally, NF-kappa B(-)CD40(-)class II(+) DC may either tolerize or sensitize T cells. Thus, while CD40(-) DC appear to "prime" or prepare T cells, the data imply that signals derived from other cells drive the generation either of Ag-specific regulatory or effector cells in vivo.     

Differential control of T regulatory cell proliferation and suppressive activity by mature plasmacytoid versus conventional spleen dendritic cells

Anergy and suppression are cardinal features of CD4(+)CD25(+)Foxp3(+) T cells (T regulatory cells (Treg)) which have been shown to be tightly controlled by the maturation state of dendritic cells (DC). However, whether lymphoid organ DC subsets exhibit different capacities to control Treg is unclear. In this study, we have analyzed, in the rat, the role of splenic CD4(+) and CD4(-) conventional DC and plasmacytoid DC (pDC) in allogeneic Treg proliferation and suppression in vitro. As expected, in the absence of exogenous IL-2, Treg did not expand in response to immature DC. Upon TLR-induced maturation, all DC became potent stimulators of CD4(+)CD25(-) T cells, whereas only TLR7- or TLR9-matured pDC induced strong proliferation of CD4(+)CD25(+)Foxp3(+) T cells in the absence of exogenous IL-2. This capacity of pDC to reverse Treg anergy required cell contact and was partially CD86 dependent and IL-2 independent. In suppression assays, Treg strongly suppressed proliferation and IL-2 and IFN-gamma production by CD4(+)CD25(-) T cells induced by mature CD4(+) and CD4(-) DC. In contrast, upon stimulation by mature pDC, proliferating Treg suppressed IL-2 production by CD25(-) cells but not their proliferation or IFN-gamma production. Taken together, these results suggest that anergy and the suppressive function of Treg are differentially controlled by DC subsets.     

MHC class I-positive dendritic cells (DC) control CD8 T cell homeostasis in vivo: T cell lymphopenia as a prerequisite for DC-mediated homeostatic proliferation of naive CD8 T cells

The sizes of peripheral T cell pools are regulated by competition for environmental signals within a given ecological T cell niche. Cytokines and MHC molecules have been identified as resources for which naive T cells compete to proliferate homeostatically in lymphopenic hosts to fill up their respective compartments. However, it still remains unclear to what extent CD4 and CD8 T cells intercompete for these resources and which role dendritic cells (DC) play in this scenario. Using transgenic mice in which only DC express MHC class I, we demonstrate that this type of APC is sufficient to trigger complete homeostatic proliferation of CD8 T cells in vivo. However, normal numbers of endogenous naive CD4 T cells, but not CD25(+)CD4(+) T regulatory cells, efficiently suppress this expansion in vivo. These findings identify DC as a major resource and a possible target for homeostatic competition between naive CD4 and CD8 T cells.     

Acquisition of MHC:Peptide Complexes by Dendritic Cells Contributes to the Generation of Antiviral CD8+ T Cell Immunity In Vivo

There is an increasing body of evidence suggesting that the transfer of preformed MHC class I:peptide complexes between a virus-infected cell and an uninfected APC, termed cross-dressing, represents an important mechanism of Ag presentation to CD8(+) T cells in host defense. However, although it has been shown that memory CD8(+) T cells can be activated by uninfected dendritic cells (DCs) cross-dressed by Ag from virus-infected parenchymal cells, it is unknown whether conditions exist during virus infection in which naive CD8(+) T cells are primed and differentiate to cytolytic effectors through cross-dressing, and indeed which DC subset would be responsible. In this study, we determine whether the transfer of MHC class I:peptide complexes between infected and uninfected murine DC plays a role in CD8(+) T cell priming to viral Ags in vivo. We show that MHC class I:peptide complexes from peptide-pulsed or virus-infected DCs are indeed acquired by splenic CD8α(-) DCs in vivo. Furthermore, the acquired MHC class I:peptide complexes are functional in that they induced Ag-specific CD8(+) T cell effectors with cytolytic function. As CD8α(-) DCs are poor cross-presenters, this may represent the main mechanism by which CD8α(-) DCs present exogenously encountered Ag to CD8(+) T cells. The sharing of Ag as preformed MHC class I:peptide complexes between infected and uninfected DCs without the restraints of Ag processing may have evolved to accurately amplify the response and also engage multiple DC subsets critical in the generation of strong antiviral immunity.     

MHC-dependent survival of naïve T cells? A complicated answer to a simple question

The differentiation and survival of developing alpha beta thymocytes depends on effective T-cell receptor (TCR) signaling upon recognition of self peptide/major histocompatibility complex (MHC) molecule ligands. Although this concept is uniformly accepted with regard to immature thymocytes, there are conflicting reports as to whether or not MHC recognition is required for survival of mature peripheral na?ve T cells. In this review, we assess these reports critically and conclude that in many cases, the differences observed in CD4(+) T-cell recovery between MHC-expressing and MHC-deficient animals can be attributed to proliferation occurring only in the MHC-expressing lymphopenic animals studied in these models systems, rather than to effects of MHC recognition on cell viability per se. Still other reports involve experimental manipulations that may have affected the intrathymic development of the T cells such that they receive a "poor" selecting signal, fail to fully mature, and thus behave more like thymocytes in their survival characteristics (i.e., show MHC dependence). With respect to CD8(+) T cells, we discuss data suggesting that some clones are more dependent upon the presence of MHC class I for survival than others. We propose that some CD8(+) T cells even in a wild-type host may behave like the manipulated CD4(+) T cells just described, and fail to mature completely with respect to their survival requirements. Although the proportion of CD8(+) cells in this MHC-dependent state is not known, the corresponding fraction among CD4(+) T cells seems to be rather small. Overall, our analysis of the available data suggests that most or all mature CD4(+) (and perhaps also many CD8(+)) T lymphocytes do not depend on self-recognition for their viability in the periphery.     

Selective dependence of H2-M3-restricted CD8 responses on IL-15

We studied whether CD8 T cell responses that are mediated by unconventional MHC class Ib molecules are IL-15 dependent in mice. CD8(+) T cell responses to Listeria monocytogenes infection that are restricted by the MHC class Ib molecule H2-M3 decreased in the absence of IL-15, whereas other primary MHC class Ib- and MHC class Ia-restricted responses were IL-15 independent. This result was confirmed in MHC class Ia-deficient mice in which IL-15 deficiency also reduced H2-M3-restricted but not all CD8 T cell responses to L. monocytogenes. IL-15 deficiency did not affect proliferation or survival of responding H2-M3-restricted CD8(+) T cells, but IL-15 was necessary to detect H2-M3-restricted CD8(+) T cells in naive mice. This finding suggests that these CD8(+) T cells require IL-15 during development, but become IL-15 independent after activation. IL-15 was necessary for the survival of most class Ib-restricted CD8(+) T cells, starting at the mature thymocyte stage in naive mice, but does not affect a distinct CD44(low)/CD122(low) subpopulation. These data suggest that the nature of the selecting MHC class Ib molecule determines whether CD8(+) T cells acquire IL-15 dependence during thymic development.     

Coordinated expression of Ig-like inhibitory MHC class I receptors and acquisition of cytotoxic function in human CD8+ T cells

MHC class I-specific inhibitory receptors are expressed by a subset of memory-phenotype CD8(+) T cells. Similar to NK cells, MHC class I-specific inhibitory receptors might subserve on T cells an important negative control that participates to the prevention of autologous damage. We analyzed here human CD8(+) T cells that express the Ig-like MHC class I-specific inhibitory receptors: killer cell Ig-like receptor (KIR) and CD85j. The cell surface expression of Ig-like inhibitory MHC class I receptors was found to correlate with an advanced stage of CD8(+) T cell maturation as evidenced by the reduced proliferative potential of KIR(+) and CD85j(+) T cells associated with their high intracytoplasmic perforin content. This concomitant regulation might represent a safety mechanism to control potentially harmful cytolytic CD8(+) T cells, by raising their activation threshold. Yet, KIR(+) and CD85j(+) T cells present distinct features. KIR(+)CD8(+) T cells are poor IFN-gamma producers upon TCR engagement. In addition, KIR are barely detectable at the surface of virus-specific T cells during the course of CMV or HIV-1 infection. By contrast, CD85j(+)CD8(+) T cells produce IFN-gamma upon TCR triggering, and represent a large fraction of virus-specific T cells. Thus, the cell surface expression of Ig-like inhibitory MHC class I receptors is associated with T cell engagement into various stages of the cytolytic differentiation pathway, and the cell surface expression of CD85j or KIR witnesses to the history of qualitatively and/or quantitatively distinct T cell activation events.     

T cell-intrinsic and -extrinsic contributions of the IFNAR/STAT1-axis to thymocyte survival

STAT1 is an essential part of interferon signaling, and STAT1-deficiency results in heightened susceptibility to infections or autoimmunity in both mice and humans. Here we report that mice lacking the IFNα/β-receptor (IFNAR1) or STAT1 display impaired deletion of autoreactive CD4(+)CD8(+)-T-cells. Strikingly, co-existence of WT T cells restored thymic elimination of self-reactive STAT1-deficient CD4(+)CD8(+)-T cells. Analysis of STAT1-deficient thymocytes further revealed reduced Bim expression, which was restored in the presence of WT T cells. These results indicate that type I interferons and STAT1 play an important role in the survival of MHC class I-restricted T cells in a T cell intrinsic and non-cell intrinsic manner that involves regulation of Bim expression through feedback provided by mature STAT1-competent T cells.     

The Src-like adaptor protein regulates GM-CSFR signaling and monocytic dendritic cell maturation

GM-CSF is an important cytokine involved in myeloid differentiation and inflammatory processes. Signaling through the GM-CSFR also plays a critical role in the generation of monocyte-derived dendritic cells (DC). In this article, we report that the Src-like adaptor protein (SLAP) functions as a negative regulator of the GM-CSFR. In bone marrow-derived DC (BM-DC) lacking SLAP and the closely related SLAP2, downregulation of GM-CSFRβ is impaired, leading to enhanced phosphorylation of Jak2 and prolonged activation of Akt and Erk1/2 in response to GM-CSF stimulation. Compared with wild-type bone marrow, SLAP/SLAP2(-/-) bone marrow gave rise to similar numbers of CD11c(+) and CD11b(+) DC, but SLAP/SLAP2(-/-) BM-DC failed to acquire high levels of MHC class II, CD80, and CD86, indicating an impairment in maturation. Furthermore, MHC class II expression in SLAP/SLAP2(-/-) BM-DC was rescued by decreasing GM-CSF concentration, suggesting that enhanced GM-CSF signaling mediates the block in maturation. In addition, SLAP/SLAP2(-/-) BM-DC produced less IL-12 and TNF-α in response to LPS compared with controls and failed to stimulate T cells in an MLR. Ag-specific T cell activation assays showed that SLAP/SLAP2(-/-) BM-DC were less robust at inducing IFN-γ secretion by DO11.10 T cells. These results indicated that SLAP-mediated GM-CSFR regulation is important for the generation of functionally mature monocytic DC.     

Comparison of the functional properties of murine dendritic cells generated in vivo with Flt3 ligand, GM-CSF and Flt3 ligand plus GM-SCF

Flt3 ligand (FL) and granulocyte-macrophage colony-stimulating factor (GM-CSF) are important growth factors for dendritic cells (DC). Substantial numbers of DC can be generated in vivo following the administration of either factor. We sought to extend our knowledge of the functional properties of these cells including their ability to prime na?ve CD8(+) T cells. In addition, we compared the nature of the DC generated in vivo with the single cytokines to those generated with the combination of FL+polyethylene glycol-modified GM-CSF (pGM-CSF). Treatment with FL+pGM-CSF yielded greater numbers of both CD11b(low) and CD11b(high) DC than with either cytokine alone, and these DC were more efficient at antigen (Ag) capture. The FL+pGM-CSF-generated CD11b(low) DC lacked expression of CD8alpha. Following treatment with LPS in vivo, all DC subsets upregulated CD40, CD80, CD86, and MHC class II expression, but surprisingly Ag capture was not downregulated and some DC subsets retained expression of intracellular MHC class II vesicles. Thus, even after activation in vivo with LPS, DC retained Ag capture properties of immature DC, and Ag presentation/costimulation properties of mature DC. Though all DC subsets stimulated CD4(+) T cell proliferation equivalently, FL-generated DC were more efficient at priming Ag-specific CD8(+) cytolytic T cells than DC generated with either pGM-CSF alone or FL+pGM-CSF, and CD11b(high) DC were more efficient at priming CD8(+) T cells than CD11b(low) DC.     

Priming of CTLs by lymphocytic choriomeningitis virus depends on dendritic cells

Appropriate activation of naive CD8(+) T cells depends on the coordinated interaction of these cells with professional APC that present antigenic peptides in the context of MHC class I molecules. It is accepted that dendritic cells (DC) are efficient in activating naive T cells and are unique in their capacity to prime CD8(+) T cell responses against exogenous cell-associated Ags. Nevertheless, it is unclear whether epitopes, derived from endogenously synthesized proteins and presented by MHC class I molecules on the surface of other APC including B cells and macrophages, can activate naive CD8(+) T cells in vivo. By infecting transgenic CD11c-DTR/GFP mice that allow conditional depletion of DC with lymphocytic choriomeningitis virus (LCMV), which infects all types of APC and elicits a vigorous CTL response, we unambiguously show that priming of LCMV-specific CD8(+) T cells is crucially dependent on DC, despite ample presence of LCMV-infected macrophages and B cells in secondary lymphoid organs.     

Exosomes as potent cell-free peptide-based vaccine. I. Dendritic cell-derived exosomes transfer functional MHC class I/peptide complexes to dendritic cells

Current immunization protocols in cancer patients involve CTL-defined tumor peptides. Mature dendritic cells (DC) are the most potent APCs for the priming of naive CD8(+) T cells, eventually leading to tumor eradication. Because DC can secrete MHC class I-bearing exosomes, we addressed whether exosomes pulsed with synthetic peptides could subserve the DC function consisting in MHC class I-restricted, peptide-specific CTL priming in vitro and in vivo. The priming of CTL restricted by HLA-A2 molecules and specific for melanoma peptides was performed: 1) using in vitro stimulations of total blood lymphocytes with autologous DC pulsed with GMP-manufactured autologous exosomes in a series of normal volunteers; 2) in HLA-A2 transgenic mice (HHD2) using exosomes harboring functional HLA-A2/Mart1 peptide complexes. In this study, we show that: 1). DC release abundant MHC class I/peptide complexes transferred within exosomes to other naive DC for efficient CD8(+) T cell priming in vitro; 2). exosomes require nature's adjuvants (mature DC) to efficiently promote the differentiation of melanoma-specific effector T lymphocytes producing IFN-gamma (Tc1) effector lymphocytes in HLA-A2 transgenic mice (HHD2). These data imply that exosomes might be a transfer mechanism of functional MHC class I/peptide complexes to DC for efficient CTL activation in vivo.     

Pervasive influence of hepatitis C virus on the phenotype of antiviral CD8+ T cells

Recent studies using MHC class I tetramers have shown that CD8(+) T cell responses against different persistent viruses vary considerably in magnitude and phenotype. At one extreme, hepatitis C virus (HCV)-specific CD8(+) T cell responses in blood are generally weak and have a phenotype that is perforin low and CCR7 high (early memory). At the other, specific responses to CMV are strong, perforin high, and CCR7 low (mature or effector memory). To examine the potential mechanisms behind this diversity, we compared CMV-specific responses in HCV-infected and healthy individuals. We find a striking difference in the phenotype of CMV-specific CD8(+) T cells between these groups. In the HCV-infected cohort, CMV-specific CD8(+) T cells lost markers associated with maturity; they had increased expression of CCR7 and reduced expression of Fas and perforin. They nevertheless responded to Ag in vitro in a manner similar to controls, with strong proliferation and appropriate acquisition of effector memory markers. The reduction in mature CD8 T cells in HCV-infected individuals may arise through either impairment or regulation of T cell stimulation, or through the early loss of mature T cells. Whatever the mechanism, HCV has a pervasive influence on the circulating CD8(+) T cell population, a novel feature that may be a hallmark of this infection.     

The relative efficiency of acquisition of MHC:peptide complexes and cross-presentation depends on dendritic cell type

Intercellular exchange of MHC molecules has been reported between many cells, including professional and nonprofessional APCs. This phenomenon may contribute to T cell immunity to pathogens. In this study, we addressed whether the transfer of MHC class I:peptide complexes between cells plays a role in T cell responses and compare this to conventional cross-presentation. We observed that dsRNA-matured bone marrow-derived dendritic cells (BMDCs) acquired peptide:MHC complexes from other BMDCs either pulsed with OVA(257-264) peptide, soluble OVA, or infected with a recombinant adenovirus expressing OVA. In addition, BMDCs were capable of acquiring MHC:peptide complexes from epithelial cells. Spleen-derived CD8alpha(+) and CD8alpha(-) dendritic cells (DCs) also acquired MHC:peptide complexes from BMDCs pulsed with OVA(257-264) peptide. However, the efficiency of acquisition by these ex vivo derived DCs is much lower than acquisition by BMDC. In all cases, the acquired MHC:peptide complexes were functional in that they induced Ag-specific CD8(+) T cell proliferation. The efficiency of MHC transfer was compared with cross-presentation for splenic CD8alpha(+) and CD8alpha(-) as well as BMDCs. CD8alpha(+) DCs were more efficient at inducing T cell proliferation when they acquired Ag via cross-presentation, the opposite was observed for BMDCs and splenic CD8alpha(-) DCs. We conclude from these observations that the relative efficiency of MHC transfer vs cross-presentation differs markedly between different DC subsets.     

Quantitation of CD8+ T cell expansion,memory, and protective immunity after immunization with peptide-coated dendritic cells

Dendritic cells (DCs) are potent APCs for naive CD8(+) T cells and are being investigated as vaccine delivery vehicles. In this study, we examine the CD8(+) T cell response to defined peptides from Listeria monocytogenes (LM), lymphocytic choriomeningitis virus, and murine CMV coated singly and in combination onto mature bone marrow-derived DCs (BMDCs). We show that immunization of mice with 2 x 10(5) mature BMDCs coated with multiple MHC class I peptides generates a significant Ag-specific CD8(+) T cell response in both the spleen and nonlymphoid organs. This immunization resulted in a peptide-specific hierarchy in the magnitude of CD8(+) T cell priming and noncoordinate kinetics in response to different peptide epitopes. Kinetics were not exclusively due to specific characteristics of the MHC class I molecule, and were not altered in an Ag-independent manner by concurrent LM infection. Mice immunized with listeriolysin O 91-99-coated BMDCs are protected against high dose challenge with virulent LM. This protection was enhanced by diversifying the memory CD8(+) T cell compartment, even in the absence of a large increase in Ag-specific CD8(+) memory T cells.     

Presentation of soluble antigens to CD8+ T cells by CpG oligodeoxynucleotide-primed human naive B cells

Naive B lymphocytes are generally thought to be poor APCs, and there is limited knowledge of their role in activation of CD8(+) T cells. In this article, we demonstrate that class I MHC Ag presentation by human naive B cells is enhanced by TLR9 agonists. Purified naive B cells were cultured with or without a TLR9 agonist (CpG oligodeoxynucleotide [ODN] 2006) for 2 d and then assessed for phenotype, endocytic activity, and their ability to induce CD8(+) T cell responses to soluble Ags. CpG ODN enhanced expression of class I MHC and the costimulatory molecule CD86 and increased endocytic activity as determined by uptake of dextran beads. Pretreatment of naive B cells with CpG ODN also enabled presentation of tetanus toxoid to CD8(+) T cells, resulting in CD8(+) T cell cytokine production and granzyme B secretion and proliferation. Likewise, CpG-activated naive B cells showed enhanced ability to cross-present CMV Ag to autologous CD8(+) T cells, resulting in proliferation of CMV-specific CD8(+) T cells. Although resting naive B cells are poor APCs, they can be activated by TLR9 agonists to serve as potent APCs for class I MHC-restricted T cell responses. This novel activity of naive B cells could be exploited for vaccine design.     

Immune evasion by Yersinia enterocolitica: differential targeting of dendritic cell subpopulations in vivo

CD4(+) T cells are essential for the control of Yersinia enterocolitica (Ye) infection in mice. Ye can inhibit dendritic cell (DC) antigen uptake and degradation, maturation and subsequently T-cell activation in vitro. Here we investigated the effects of Ye infection on splenic DCs and T-cell proliferation in an experimental mouse infection model. We found that OVA-specific CD4(+) T cells had a reduced potential to proliferate when stimulated with OVA after infection with Ye compared to control mice. Additionally, proliferation of OVA-specific CD4(+) T cells was markedly reduced when cultured with splenic CD8α(+) DCs from Ye infected mice in the presence of OVA. In contrast, T-cell proliferation was not impaired in cultures with CD4(+) or CD4(-)CD8α(-) DCs isolated from Ye infected mice. However, OVA uptake and degradation as well as cytokine production were impaired in CD8α(+) DCs, but not in CD4(+) and CD4(-)CD8α(-) DCs after Ye infection. Pathogenicity factors (Yops) from Ye were most frequently injected into CD8α(+) DCs, resulting in less MHC class II and CD86 expression than on non-injected CD8α(+) DCs. Three days post infection with Ye the number of splenic CD8α(+) and CD4(+) DCs was reduced by 50% and 90%, respectively. The decreased number of DC subsets, which was dependent on TLR4 and TRIF signaling, was the result of a faster proliferation and suppressed de novo DC generation. Together, we show that Ye infection negatively regulates the stimulatory capacity of some but not all splenic DC subpopulations in vivo. This leads to differential antigen uptake and degradation, cytokine production, cell loss, and cell death rates in various DC subpopulations. The data suggest that these effects might be caused directly by injection of Yops into DCs and indirectly by affecting the homeostasis of CD4(+) and CD8α(+) DCs. These events may contribute to reduced T-cell proliferation and immune evasion of Ye.