NKT cells enhance CD4+ and CD8+ T cell responses to soluble antigen in vivo through direct interaction with dendritic cells

Modification in the function of dendritic cells (DC), such as that achieved by microbial stimuli or T cell help, plays a critical role in determining the quality and size of adaptive responses to Ag. NKT cells bearing an invariant TCR (iNKT cells) restricted by nonpolymorphic CD1d molecules may constitute a readily available source of help for DC. We therefore examined T cell responses to i.v. injection of soluble Ag in the presence or the absence of iNKT cell stimulation with the CD1d-binding glycolipid alpha-galactosylceramide (alpha-GalCer). Considerably enhanced CD4(+) and CD8(+) T cell responses were observed when alpha-GalCer was administered at the same time as or close to OVA injection. This enhancement was dependent on the involvement of iNKT cells and CD1d molecules and required CD40 signaling. Studies in IFN-gammaR(-/-) mice indicated that IFN-gamma was not required for the adjuvant effect of alpha-GalCer. Consistent with this result, enhanced T cell responses were observed using OCH, an analog of alpha-GalCer with a truncated sphingosine chain and a reduced capacity to induce IFN-gamma. Splenic DC from alpha-GalCer-treated animals expressed high levels of costimulatory molecules, suggesting maturation in response to iNKT cell activation. Furthermore, studies with cultured DC indicated that potentiation of T cell responses required presentation of specific peptide and alpha-GalCer by the same DC, implying conditioning of DC by iNKT cells. The iNKT-enhanced T cell responses resisted challenge with OVA-expressing tumors, whereas responses induced in the absence of iNKT stimulation did not. Thus, iNKT cells exert a significant influence on the efficacy of immune responses to soluble Ag by modulating DC function.     

Follicular helper NKT cells induce limited B cell responses and germinal center formation in the absence of CD4(+) T cell help

B cells require MHC class II (MHC II)-restricted cognate help and CD40 engagement by CD4(+) T follicular helper (T(FH)) cells to form germinal centers and long-lasting Ab responses. Invariant NKT (iNKT) cells are innate-like lymphocytes that jumpstart the adaptive immune response when activated by the CD1d-restricted lipid α-galactosylceramide (αGalCer). We previously observed that immunization of mice lacking CD4(+) T cells (MHC II(-/-)) elicits specific IgG responses only when protein Ags are mixed with αGalCer. In this study, we investigated the mechanisms underpinning this observation. We find that induction of Ag-specific Ab responses in MHC II(-/-) mice upon immunization with protein Ags mixed with αGalCer requires CD1d expression and CD40 engagement on B cells, suggesting that iNKT cells provide CD1d-restricted cognate help for B cells. Remarkably, splenic iNKT cells from immunized MHC II(-/-) mice display a typical CXCR5(hi)programmed death-1(hi)ICOS(hi)Bcl-6(hi) T(FH) phenotype and induce germinal centers. The specific IgG response induced in MHC II(-/-) mice has shorter duration than that developing in CD4-competent animals, suggesting that iNKT(FH) cells preferentially induce transient rather than long-lived Ab responses. Together, these results suggest that iNKT cells can be co-opted into the follicular helper function, yet iNKT(FH) and CD4(+) T(FH) cells display distinct helper features, consistent with the notion that these two cell subsets play nonredundant functions throughout immune responses.     

iNKT Cells Suppress the CD8(+) T Cell Response to a Murine Burkitt's-Like B Cell Lymphoma

The T cell response to B cell lymphomas differs from the majority of solid tumors in that the malignant cells themselves are derived from B lymphocytes, key players in immune response. B cell lymphomas are therefore well situated to manipulate their surrounding microenvironment to enhance tumor growth and minimize anti-tumor T cell responses. We analyzed the effect of T cells on the growth of a transplantable B cell lymphoma and found that iNKT cells suppressed the anti-tumor CD8(+) T cell response. Lymphoma cells transplanted into syngeneic wild type (WT) mice or Jalpha18(-/-) mice that specifically lack iNKT cells grew initially at the same rate, but only the mice lacking iNKT cells were able to reject the lymphoma. This effect was due to the enhanced activity of tumor-specific CD8(+) T cells in the absence of iNKT cells, and could be partially reversed by reconstitution of iNKT cells in Jalpha 18(-/-) mice. Treatment of tumor-bearing WT mice with alpha -galactosyl ceramide, an activating ligand for iNKT cells, reduced the number of tumor-specific CD8(+) T cells. In contrast, lymphoma growth in CD1d1(-/-) mice that lack both iNKT and type II NKT cells was similar to that in WT mice, suggesting that type II NKT cells are required for full activation of the anti-tumor immune response. This study reveals a tumor-promoting role for iNKT cells and suggests their capacity to inhibit the CD8(+) T cell response to B cell lymphoma by opposing the effects of type II NKT cells.     

Antigen specificity acquisition of adoptive CD4+ regulatory T cells via acquired peptide-MHC class I complexes

The Ag-specific CD4(+) regulatory T (Tr) cells play an important role in immune suppression in autoimmune diseases and antitumor immunity. However, the molecular mechanism for Ag-specificity acquisition of adoptive CD4(+) Tr cells is unclear. In this study, we generated IL-10- and IFN-gamma-expressing type 1 CD4(+) Tr (Tr1) cells by stimulation of transgenic OT II mouse-derived naive CD4(+) T cells with IL-10-expressing adenovirus (AdV(IL-10))-transfected and OVA-pulsed dendritic cells (DC(OVA/IL-10)). We demonstrated that both in vitro and in vivo DC(OVA/IL-10)-stimulated CD4(+) Tr1 cells acquired OVA peptide MHC class (pMHC) I which targets CD4(+) Tr1 cells suppressive effect via an IL-10-mediated mechanism onto CD8(+) T cells, leading to an enhanced suppression of DC(OVA)-induced CD8(+) T cell responses and antitumor immunity against OVA-expressing murine B16 melanoma cells by approximately 700% relative to analogous CD4(+) Tr1 cells without acquired pMHC I. Interestingly, the nonspecific CD4(+)25(+) Tr cells can also become OVA Ag specific and more immunosuppressive in inhibition of OVA-specific CD8(+) T cell responses and antitumor immunity after uptake of DC(OVA)-released exosomal pMHC I complexes. Taken together, the Ag-specificity acquisition of CD4(+) Tr cells via acquiring DC's pMHC I may be an important mean in augmenting CD4(+) Tr cell suppression.     

Cross-primed CD8+ cytotoxic T cells induce severe Helicobacter-associated gastritis in the absence of CD4+ T cells

BACKGROUND: Although previous studies have reported important roles of CD4(+) type 1-helper T cells and regulatory T cells in Helicobacter-associated gastritis, the significance of CD8(+) cytotoxic T cells remains unknown. To study the roles of CD8(+) T cells, we examined the immune response in the gastric mucosa of Helicobacter felis-infected major histocompatibility complex (MHC) class II-deficient (II(-/-)) mice, which lack CD4(+) T cells. MATERIALS AND METHODS: Stomachs from H. felis-infected wild-type and infected MHC II(-/-) mice were examined histologically and immunohistochemically. Gastric acidity and serum levels of anti-H. felis antibodies were measured. The expression of pro-inflammatory and anti-inflammatory cytokine, Fas-ligand, perforin, and Foxp3 genes in the gastric mucosa was investigated. RESULTS: H. felis-infected MHC II(-/-) mice developed severe gastritis, accompanied by marked infiltration of CD8(+) cells. At 1 and 2 months after inoculation, mucosal inflammation and atrophy were more severe in MHC II(-/-) mice, although gastritis had reached similar advanced stages at 3 months after inoculation. There was little infiltration of CD4(+) cells, and no Foxp3-positive cells were detected in the gastric mucosa of the infected MHC II(-/-) mice. The expression of the interleukin-1beta and Fas-ligand genes was up regulated, but that of Foxp3 was down regulated in the infected MHC II(-/-) mice. Serum levels of anti-H. felis antibodies were lower in the infected MHC II(-/-) mice, despite severe gastritis. CONCLUSIONS: The present study suggests that cross-primed CD8(+) cytotoxic T cells can induce severe H.-associated gastritis in the absence of CD4(+) helper T cells and that Foxp3-positive cells may have an important role in the control of gastric inflammation.     

NKT cell-derived RANTES recruits APCs and CD8+ T cells to the spleen during the generation of regulatory T cells in tolerance

The induction of peripheral tolerance via immune privileged sites such as the eye requires splenic colocalization of NKT cells and CD1d(+) tolerogenic F4/80(+) APCs, both of which are needed for the generation of CD8(+)-regulatory T (Tr) cells. Whereas tolerogenic APCs secrete the chemokine macrophage-inflammatory protein-2 for the purpose of recruiting NKT cells, the signals responsible for recruiting potential Tr cells and additional APCs to the spleen are not known. Here we examined the ability of CD1d-stimulated NKT cells to produce chemokines that can recruit other cells needed for tolerance. Our results show that NKT cells stimulated by either CD1d-transfected fibroblasts in vitro or CD1d(+) tolerogenic APCs both in vivo and ex vivo produced RANTES in a CD1d-dependent manner. The requirement for RANTES in tolerance was demonstrated by studies in which RANTES blockade in vivo prevented not only APC accumulation in the spleen but also the generation of CD8(+) Tr cells that suppress Th1 immunity. Thus, CD1d-restricted NKT cells provide critical signals for orchestrating the accumulation of cells needed for tolerance induction. These data expand our current knowledge of RANTES beyond its role in Th1 immune responses to show its importance in tolerance induction and add a novel aspect to our understanding of the role of NKT cells in tolerance. Understanding the precise mechanisms involved in tolerance induction may lead to more effective therapeutic strategies for autoimmunity and graft rejection.     

CD103- and CD103+ bronchial lymph node dendritic cells are specialized in presenting and cross-presenting innocuous antigen to CD4+ and CD8+ T cells

Dendritic cells (DC) are able to capture, process, and present exogenous Ag to CD8(+) T lymphocytes through MHC class I, a process referred to as cross-presentation. In this study, we demonstrate that CD103(+) (CD11c(high)CD11b(low)) and CD103(-) (CD11c(int)CD11b(high)) DC residing in the lung-draining bronchial lymph node (brLN) have evolved to acquire opposing functions in presenting innocuous inhaled Ag. Thus, under tolerogenic conditions, CD103(-) DC are specialized in presenting innocuous Ag to CD4(+) T cells, whereas CD103(+) DC, which do not express CD8alpha, are specialized in presenting Ag exclusively to CD8(+) T cells. In CCR7-deficient but not in plt/plt mice, Ag-carrying CD103(+) DC are largely absent in the brLN, although CD103(+) DC are present in the lung of CCR7-deficient mice. As a consequence, adoptively transferred CD8(+) T cells can be activated under tolerizing conditions in plt/plt but not in CCR7-deficient mice. These data reveal that CD103(+) brLN DC are specialized in cross-presenting innocuous inhaled Ag in vivo. Because these cells are largely absent in CCR7(-/-) mice, our findings strongly suggest that brLN CD103(+) DC are lung-derived and that expression of CCR7 is required for their migration from the lung into its draining lymph node.     

IL-15 expands unconventional CD8alphaalphaNK1.1+ T cells but not Valpha14Jalpha18+ NKT cells

Despite recent gains in knowledge regarding CD1d-restricted NKT cells, very little is understood of non-CD1d-restricted NKT cells such as CD8(+)NK1.1(+) T cells, in part because of the very small proportion of these cells in the periphery. In this study we took advantage of the high number of CD8(+)NK1.1(+) T cells in IL-15-transgenic mice to characterize this T cell population. In the IL-15-transgenic mice, the absolute number of CD1d-tetramer(+) NKT cells did not increase, although IL-15 has been shown to play a critical role in the development and expansion of these cells. The CD8(+)NK1.1(+) T cells in the IL-15-transgenic mice did not react with CD1d-tetramer. Approximately 50% of CD8(+)NK1.1(+) T cells were CD8alphaalpha. In contrast to CD4(+)NK1.1(+) T cells, which were mostly CD1d-restricted NKT cells and of which approximately 70% were CD69(+)CD44(+), approximately 70% of CD8(+)NK1.1(+) T cells were CD69(-)CD44(+). We could also expand similar CD8alphaalphaNK1.1(+) T cells but not CD4(+) NKT cells from CD8alpha(+)beta(-) bone marrow cells cultured ex vivo with IL-15. These results indicate that the increased CD8alphaalphaNK1.1(+) T cells are not activated conventional CD8(+) T cells and do not arise from conventional CD8alphabeta precursors. CD8alphaalphaNK1.1(+) T cells produced very large amounts of IFN-gamma and degranulated upon TCR activation. These results suggest that high levels of IL-15 induce expansion or differentiation of a novel NK1.1(+) T cell subset, CD8alphaalphaNK1.1(+) T cells, and that IL-15-transgenic mice may be a useful resource for studying the functional relevance of CD8(+)NK1.1(+) T cells.     

Functional characterization of MHC class II-restricted CD8+CD4- and CD8-CD4- T cell responses to infection in CD4-/- mice

Classical CD4(+) and CD8(+) T cells recognize Ag presented by MHC class II (MHCII) and MHC class I (MHCI), respectively. However, our results show that CD4(-/-) mice mount a strong, readily detectable CD8(+) T cell response to MHCII-restricted epitopes after a primary bacterial or viral infection. These MHCII-restricted CD8(+)CD4(-) T cells are more similar to classical CD8(+) T cells than to CD4(+) T cells in their expression of effector functions during a primary infection, yet they also differ from MHCI-restricted CD8(+) T cells by their inability to produce high levels of the cytolytic molecule granzyme B. After resolution of a primary infection, epitope-specific MHCII-restricted T cells in CD4(-/-) mice persist for a long period of time as memory T cells. Surprisingly, upon reinfection the secondary MHCII-restricted response in CD4(-/-) mice consists mainly of CD8(-)CD4(-) T cells. In contrast to CD8(+) T cells, MHCII-restricted CD8(-)CD4(-) T cells are capable of producing IL-2 in addition to IFN-gamma and thus appear to have attributes characteristic of CD4(+) T cells rather than CD8(+) T cells. Therefore, MHCII-restricted T cells in CD4(-/-) mice do not share all phenotypic and functional characteristics with MHCI-restricted CD8(+) T cells or with MHCII-restricted CD4(+) T cells, but, rather, adopt attributes from each of these subsets. These results have implications for understanding thymic T cell selection and for elucidating the mechanisms regulating the peripheral immune response and memory differentiation.     

Potent tumor-specific protection ignited by adoptively transferred CD4+ T cells

Administration of anti-CD25 mAb before an aggressive murine breast tumor inoculation provoked effective antitumor immunity. Compared with CD4(+) T cells purified from anti-CD25 mAb-pretreated mice that did not reject tumor, CD4(+) T cells purified from anti-CD25 mAb-pretreated mice that rejected tumor stimulated by dendritic cells (DCs) produced more IFN-gamma and IL-2, and less IL-17 in vitro, and ignited protective antitumor immunity in vivo in an adoptive transfer model. Tumor Ag-loaded DCs activated naive CD8(+) T cells in the presence of these CD4(+) T cells in vitro. Tumor Ag and adoptively transferred CD4(+) T cells were both required for inducing a long-term tumor-specific IFN-gamma-producing cellular response and potent protective antitumor activity. Although adoptively transferred CD4(+) T cells ignited effective tumor-specific antitumor immunity in wild-type mice, they failed to do so in endogenous NK cell-depleted, Gr-1(+) cell-depleted, CD40(-/-), CD11c(+) DC-depleted, B cell(-/-), CD8(+) T cell-depleted, or IFN-gamma(-/-) mice. Collectively, the data suggest that adoptively transferred CD4(+) T cells orchestrate both endogenous innate and adaptive immunity to generate effective tumor-specific long-term protective antitumor immunity. The data also demonstrate the pivotal role of endogenous DCs in the tumor-specific protection ignited by adoptively transferred CD4(+) T cells. Thus, these findings highlight the importance of adoptively transferred CD4(+) T cells, as well as host immune components, in generating effective tumor-specific long-term antitumor activity.     

Type I IFN-induced, NKT cell-mediated negative control of CD8 T cell priming by dendritic cells

We investigated the negative effect of type I IFN (IFN-I) on the priming of specific CD8 T cell immunity. Priming of murine CD8 T cells is down-modulated if Ag is codelivered with IFN-I-inducing polyinosinic:polycytidylic acid (pI/C) that induces (NK cell- and T/B cell-independent) acute changes in the composition and surface phenotype of dendritic cells (DC). In wild-type but not IFN-I receptor-deficient mice, pI/C reduces the plasmacytoid DC but expands the CD8(+) conventional DC (cDC) population and up-regulates surface expression of activation-associated (CD69, BST2), MHC (class I/II), costimulator (CD40, CD80/CD86), and coinhibitor (PD-L1/L2) molecules by cDC. Naive T cells are efficiently primed in vitro by IFN-I-stimulated CD8 cDC (the key APC involved in CD8 T cell priming) although these DC produced less IL-12 p40 and IL-6. pI/C (IFN-I)-mediated down modulation of CD8 T cell priming in vivo was not observed in NKT cell-deficient CD1d(-/-) mice. CD8 cDC from pI/C-treated mice inefficiently stimulated IFN-gamma, IL-4, and IL-2 responses of NKT cells. In vitro, CD8 cDC that had activated NKT cells in the presence of IFN-I primed CD8 T cells that produced less IFN-gamma but more IL-10. The described immunosuppressive effect of IFN-I thus involves an NKT cell-mediated change in the phenotype of CD8 cDC that favors priming of IL-10-producing CD8 T cells. In the presence of IFN-I, NKT cells hence impair the competence of CD8 cDC to prime proinflammatory CD8 T cell responses.     

A DNA vaccine encoding multiple HIV CD4 epitopes elicits vigorous polyfunctional, long-lived CD4+ and CD8+ T cell responses

T-cell based vaccines against HIV have the goal of limiting both transmission and disease progression by inducing broad and functionally relevant T cell responses. Moreover, polyfunctional and long-lived specific memory T cells have been associated to vaccine-induced protection. CD4(+) T cells are important for the generation and maintenance of functional CD8(+) cytotoxic T cells. We have recently developed a DNA vaccine encoding 18 conserved multiple HLA-DR-binding HIV-1 CD4 epitopes (HIVBr18), capable of eliciting broad CD4(+) T cell responses in multiple HLA class II transgenic mice. Here, we evaluated the breadth and functional profile of HIVBr18-induced immune responses in BALB/c mice. Immunized mice displayed high-magnitude, broad CD4(+)/CD8(+) T cell responses, and 8/18 vaccine-encoded peptides were recognized. In addition, HIVBr18 immunization was able to induce polyfunctional CD4(+) and CD8(+) T cells that proliferate and produce any two cytokines (IFNγ/TNFα, IFNγ/IL-2 or TNFα/IL-2) simultaneously in response to HIV-1 peptides. For CD4(+) T cells exclusively, we also detected cells that proliferate and produce all three tested cytokines simultaneously (IFNγ/TNFα/IL-2). The vaccine also generated long-lived central and effector memory CD4(+) T cells, a desirable feature for T-cell based vaccines. By virtue of inducing broad, polyfunctional and long-lived T cell responses against conserved CD4(+) T cell epitopes, combined administration of this vaccine concept may provide sustained help for CD8(+) T cells and antibody responses- elicited by other HIV immunogens.     

Invariant NKT cells promote CD8+ cytotoxic T cell responses by inducing CD70 expression on dendritic cells

Activation of invariant NK T (iNKT) cells with the glycolipid alpha-galactosylceramide promotes CD8(+) cytotoxic T cell responses, a property that has been used to enhance the efficacy of antitumor vaccines. Using chimeric mice, we now show that the adjuvant properties of iNKT cells require that CD40 triggering and Ag presentation to CD8(+) T cells occur on the same APCs. We demonstrate that injection of alpha-galactosylceramide triggers CD70 expression on splenic T cell zone dendritic cells and that this is dependent on CD40 signaling. Importantly, we show that blocking the interaction between CD70 and CD27, its costimulatory receptor on T cells, abrogates the ability of iNKT cells to promote a CD8(+) T cell response and abolishes the efficacy of alpha-GalCer as an adjuvant for antitumor vaccines. These results define a key role for CD70 in linking the innate response of iNKT cells to the activation of CD8(+) T cells.     

Ex vivo activated OVA specific and non-specific CD4+CD25+ regulatory T cells exhibit comparable suppression to OVA mediated T cell responses

CD4+CD25+ regulatory T cells (Tr) are important in maintaining immune tolerance to self-antigen (Ag) and preventing autoimmunity. Reduced number and inadequate function of Tr are observed in chronic autoimmune diseases. Adoptively transferred Tr effectively suppress ongoing autoimmune disease in multiple animal models. Therefore, strategies to modulate Tr have become an attractive approach to control autoimmunity. Activation of Tr is necessary for their optimal immune regulatory function. However, due to the low ratio of Tr to any given antigen (Ag) and the unknown nature of Ag in many autoimmune diseases, specific activation is not practical for potential therapeutic intervention. It has been shown in animal models that once activated, Tr can exhibit immune suppression in a bystander Ag-non-specific fashion, suggesting the effector phase of Tr is Ag independent. To investigate whether the immune suppression by activated bystander Tr is as potent as that of the Ag specific Tr, Tr cells were isolated from BALB/c or ovalbumin (OVA) specific T cell receptor (TCR) transgenic mice (DO11.10) and their immune suppression of an OVA specific T cell response was compared. We found that once activated ex vivo, Tr from BALB/c and DO11.10 mice exhibited comparable inhibition on OVA specific T cell responses as determined by T cell proliferation and cytokine production. Furthermore, their immune suppression function was compared in a delayed type hypersensitivity (DTH) model induced by OVA specific T cells. Again, OVA specific and non-specific Tr exhibited similar inhibition of the DTH response. Taken together, the results indicate that ex vivo activated Ag-non-specific Tr are as efficient as Ag specific Tr in immune suppression, therefore our study provides additional evidence suggesting the possibility of applying ex vivo activated Tr therapy for the control of autoimmunity.     

CD4+ and CD8+ T cells exhibit differential requirements for CCR7-mediated antigen transport during influenza infection

Upon encounter of viral Ags in an inflammatory environment, dendritic cells up-regulate costimulatory molecules and the chemokine receptor CCR7, with the latter being pivotal for their migration to the lymph node. By utilizing mice deficient in CCR7, we have examined the requirement of dendritic cell-mediated Ag transport from the lung to the draining lymph node for the induction of anti-influenza immune responses in vivo. We found that CCR7-mediated migration of dendritic cells was more crucial for CD8(+) T cell than CD4(+) T cell responses. While no specific CD8(+) T cell response could be detected in the airways or lymphoid tissues during the primary infection, prolonged infection in CCR7-deficient mice did result in a sustained inflammatory chemokine profile, which led to nonspecific CD8(+) T cell recruitment to the airways. The recruitment of influenza-specific CD4(+) T cells to the airways was also below levels of detection in the absence of CCR7 signaling, although a small influenza-specific CD4(+) T cell population was detectable in the draining lymph node, which was sufficient for the generation of class-switched anti-influenza Abs and a normal CD4(+) T cell memory population. Overall, our data show that CCR7-mediated active Ag transport is differentially required for CD4(+) and CD8(+) T cell expansion during influenza infection.     

Low-dose antigen promotes induction of FOXP3 in human CD4+ T cells

Low Ag dose promotes induction and persistence of regulatory T cells (Tregs) in mice, yet few studies have addressed the role of Ag dose in the induction of adaptive CD4(+)FOXP3(+) Tregs in humans. To this end, we examined the level of FOXP3 expression in human CD4(+)CD25(-) T cells upon activation with autologous APCs and varying doses of peptide. Ag-specific T cells expressing FOXP3 were identified by flow cytometry using MHC class II tetramer (Tmr). We found an inverse relationship between Ag dose and the frequency of FOXP3(+) cells for both foreign Ag-specific and self Ag-specific T cells. Through studies of FOXP3 locus demethylation and helios expression, we determined that variation in the frequency of Tmr(+)FOXP3(+) T cells was not due to expansion of natural Tregs, but instead, we found that induction, proliferation, and persistence of FOXP3(+) cells was similar in high- and low-dose cultures, whereas proliferation of FOXP3(-) T cells was favored in high Ag dose cultures. The frequency of FOXP3(+) cells positively correlated with suppressive function, indicative of adaptive Treg generation. The frequency of FOXP3(+) cells was maintained with IL-2, but not upon restimulation with Ag. Together, these data suggest that low Ag dose favors the transient generation of human Ag-specific adaptive Tregs over the proliferation of Ag-specific FOXP3(-) effector T cells. These adaptive Tregs could function to reduce ongoing inflammatory responses and promote low-dose tolerance in humans, especially when Ag exposure and tolerance is transient.     

CD40 engagement enhances antigen-presenting langerhans cell priming of IFN-gamma-producing CD4+ and CD8+ T cells independently of IL-12

The delivery of CD40 signaling to APCs during T cell priming enhances many T cell-mediated immune responses. Although CD40 signaling up-regulates APC production of IL-12, the impact of this increased production on T cell priming is unclear. In this study an IL-12-independent T cell-mediated immune response, contact hypersensitivity (CHS), was used to further investigate the effect of CD40 ligation on the phenotypic development of Ag-specific CD4(+) and CD8(+) T cells. Normally, sensitization for CHS responses induces hapten-specific CD4(+) T cells producing type 2 cytokines and CD8(+) T cells producing IFN-gamma. Treatment of mice with agonist anti-CD40 mAb during sensitization with the hapten 2,4-dinitrofluorobenzene resulted in CHS responses of increased magnitude and duration. These augmented responses in anti-CD40 Ab-treated mice correlated with increased numbers of hapten-specific CD4(+) and CD8(+) T cells producing IFN-gamma in the skin draining lymph nodes. Identical results were observed using IL-12(-/-) mice, indicating that CD40 ligation promotes CHS responses and development of IFN-gamma-producing CD4(+) and CD8(+) T cells in the absence of IL-12. Engagement of CD40 on hapten-presenting Langerhans cells (hpLC) up-regulated the expression of both class I and class II MHC and promoted hpLC migration into the T cell priming site. These results indicate that hpLC stimulated by CD40 ligation use a mechanism distinct from increased IL-12 production to promote Ag-specific T cell development to IFN-gamma-producing cells.     

Cutting edge: Lipopolysaccharide induces IL-10-producing regulatory CD4+ T cells that suppress the CD8+ T cell response

TLR ligands are potent activators of dendritic cells and therefore function as adjuvants for the induction of immune responses. We analyzed the capacity of TLR ligands to enhance CD8+ T cell responses toward soluble protein Ag. Immunization with OVA together with LPS or poly(I:C) elicited weak CD8+ T cell responses in wild-type C57BL/6 mice. Surprisingly, these responses were greatly increased in mice lacking CD4+ T cells indicating the induction of regulatory CD4+ T cells. In vivo, neutralization of IL-10 completely restored CD8+ T cell responses in wild-type mice and OVA-specific IL-10 producing CD4+ T cells were detected after immunization with OVA plus LPS. Our study shows that TLR ligands not only activate the immune system but simultaneously induce Ag specific, IL-10-producing regulatory Tr1 cells that strongly suppress CD8+ T cell responses. In this way, excessive activation of the immune system may be prevented.     

Platelet factor 4 differentially modulates CD4+CD25+ (regulatory) versus CD4+CD25- (nonregulatory) T cells

Active suppression mediated by CD4(+)CD25(+) T regulatory (Tr) cells plays an important role in the down-regulation of T cell responses to both foreign and self-Ags. Platelet factor 4 (PF4), a platelet-derived CXC chemokine, has been shown to strongly inhibit T cell proliferation as well as IFN-gamma and IL-2 release by isolated T cells. In this report we show that human PF4 stimulates proliferation of the naturally anergic human CD4(+)CD25(+) Tr cells while inhibiting proliferation of CD4(+)CD25(-) T cells. In coculture experiments we found that CD4(+)CD25(+) Tr cells exposed to PF4 lose the ability to inhibit the proliferative response of CD4(+)CD25(-) T cells. Our findings suggest that human PF4, by inducing Tr cell proliferation while impairing Tr cell function, may play a previously unrecognized role in the regulation of human immune responses. Because platelets are the sole source of PF4 in the circulation, these findings may be relevant to the pathogenesis of certain immune-mediated disorders associated with platelet activation, such as heparin-induced thrombocytopenia and autoimmune thrombocytopenic purpura.     

Cutting edge: analysis of human V alpha 24+CD8+ NK T cells activated by alpha-galactosylceramide-pulsed monocyte-derived dendritic cells

Human Valpha24(+) NKT cells constitute a counterpart of mouse Valpha14(+) NKT cells, both of which use an invariant TCR-alpha chain. The human Valpha24(+) NKT cells as well as mouse Valpha14(+) NKT cells are activated by glycolipids in a CD1d-restricted manner and produce many immunomodulatory cytokines, possibly affecting the immune balance. In mice, it has been considered from extensive investigations that Valpha14(+)CD8(+) NKT cells that express invariant TCR do not exist. Here we introduce human Valpha24(+)CD8(+) NKT cells. These cells share important features of Valpha24(+) NKT cells in common, but in contrast to CD4(-)CD8(-) (double-negative) or CD4(+) Valpha24(+) NKT cells, they do not produce IL-4. Our discovery may extend and deepen the research field of Valpha24(+) NKT cells as well as help to understand the mechanism of the immune balance-related diseases.