Replication-defective viruses modulate immune responses.

By immunizing inbred mice with purified replication-competent, defective virus particles, or an admixture of the two, differential effects on the cellular immune system have been uncovered. Defective virus, exemplified by the vesicular stomatitis virus (VSV) defective interfering particle (DI 0.33), induced in BALB/c mice low levels of proliferating, IL-2 secreting, and cytolytic Ag-specific T lymphocytes. This was not caused by a dominant suppressor cell response, or by a failure to stimulate lymphokine-secreting cells, but appeared to reflect a reduced efficiency of priming as compared with standard virus. Mice primed with a mixture of wt and DI virus showed reduced proliferation compared with mice primed with wt virus. When histocompatible target cells were sensitized by pure DI particles, they were neither recognized nor lysed by CD8+ CTL. Cells co-infected with wt and DI particles were not as readily lysed by CD8+ CTL as cells infected by VSV alone. The extent of this reduction was dependent on the concentration of DI particles. This suggests that DI particles may have prevented the proper presentation of endogenously synthesized Ag for recognition by CD8+ CTL. Metabolic labeling studies indicated that the presence of DI particles suppressed the synthesis of viral proteins in dually infected cells. However, CD4+ T lymphocyte clones recognized and efficiently lysed histocompatible Ia+ cells infected with DI particles alone or co-infected with replication-competent and defective virus.     

Isotype-specific immunoregulation. Systemic antigen induces splenic T contrasuppressor cells which support IgM and IgG subclass but not IgA responses

In the present study, we have isolated and characterized the Lyt-1+, -2- T contrasuppressor (Tcs) cells from mice systemically primed with SRBC. Adoptive transfer of splenic Tcs cells from these mice abrogates oral tolerance and supports IgM and IgG anti-SRBC plaque-forming cell (PFC) responses; however, unlike the responses seen after transfer of Tcs cells derived from orally primed mice, low IgA responses were seen. Mice systemically primed with lower SRBC doses (0.01 to 1%) exhibited contrasuppression only within the L3T4- T cell subset, whereas mice primed with a high dose of SRBC (10%), harbored Lyt-1+, -2- Tcs cells in both the L3T4+ and L3T4- subsets. Both the L3T4- and L3T4+ Tcs cell subsets supported IgM and IgG responses when adoptively transferred to orally tolerized mice, and when added to tolerized spleen cell cultures. Splenic Tcs cells from systemically primed mice supported mainly IgG1 and IgG2b subclass anti-SRBC PFC responses, a pattern also seen with Tcs cells derived from orally primed mice. Both L3T4+ and L3T4- Tcs cells from systemically primed mice exhibited well established characteristics of contrasuppressor cells including binding to Vicia villosa lectin and expression of I-J. The splenic effector Tcs cells which support IgM, IgG1 and IgG2b anti-SRBC PFC responses are antigen-specific, since both L3T4- and L3T4+ Tcs cells from spleens of mice primed with 10% SRBC reverse tolerance to SRBC, but not to horse erythrocytes (HRBC). Further, both L3T4- and L3T4+ Tcs cells from HRBC-primed mice reverse tolerance to IgM and IgG anti-HRBC, but not to anti-SRBC responses. Isolation of T3-positive Lyt-1+, -2- and L3T4- Tcs cell subsets by flow cytometry followed by adoptive transfer, showed that effector Tcs cells express T3 and presumably contain an Ag-R (TCR-T3 complex). These studies show that systemic priming with heterologous RBC induces splenic Ag specific Tcs cells in a dose-dependent manner, which support IgM and IgG subclass responses, but not IgA responses.     

Functional reconstitution of class II MHC-restricted T cell immunity mediated by retroviral transfer of the alpha beta TCR complex

Transfer of the alphabeta TCR genes into T lymphocytes will provide a means to enhance Ag-specific immunity by increasing the frequency of tumor- or pathogen-specific T lymphocytes. We generated an efficient alphabeta TCR gene transfer system using two independent monocistronic retrovirus vectors harboring either of the class II MHC-restricted alpha or beta TCR genes specific for chicken OVA. The system enabled us to express the clonotypic TCR in 44% of the CD4+ T cells. The transduced cells showed a remarkable response to OVA323-339 peptide in the in vitro culture system, and the response to the Ag was comparable with those of the T lymphocytes derived from transgenic mice harboring OVA-specific TCR. Adoptive transfer of the TCR-transduced cells in mice induced the Ag-specific delayed-type hypersensitivity in response to OVA323-339 challenge. These results indicate that alphabeta TCR gene transfer into peripheral T lymphocytes can reconstitute Ag-specific immunity. We here propose that this method provides a basis for a new approach to manipulation of immune reactions and immunotherapy.     

Repeated intratracheal challenge with particulate antigen modulates murine lung cytokines

When lungs of experimental animals are repeatedly challenged with Ag, pulmonary inflammation wanes via unknown mechanisms. We hypothesized that changes in the balance of lung cytokines are responsible for immune down-regulation to repeated Ag challenge. We used intratracheal (IT) challenge of primed C57BL/6 mice with SRBC and on various days after single (1IT) or triple (3IT) challenge counted lung inflammatory cells and measured whole-lung cytokine mRNA and protein concentrations using RT-PCR and ELISA. We found that lung lymphocyte numbers and parenchymal lung inflammation decreased significantly at days 6 and 9 after final Ag challenge in 3IT mice compared with 1IT mice. Lungs of 3IT mice showed the following changes in relative mRNA expression: an earlier peak in IL-10, decreased IL-1beta, and a change from a Th2 response in 1IT mice to a Th1 response in 3IT mice (with pronounced increases in IL-12, IL-18, and IFN-gamma and decreased IL-4, IL-13, and IL-5). Similar types of changes were seen in whole-lung protein concentrations for TNF-alpha, IL-10, IL-12 p40, IFN-gamma, and IL-4. Additionally, mRNA expression of the endothelial selectins CD62E and CD62P decreased and lung lymphocyte apoptosis increased in the 3IT group. Thus, physiologic down-regulation of the pulmonary immune response to repeated Ag exposure is characterized by increased anti- and decreased proinflammatory cytokines that accompanies Th1 polarization. Similar mechanisms may act to minimize chronic lung inflammation in the majority of normal humans who do not develop progressive lung pathology when repeatedly exposed to inhaled or aspirated environmental Ags.     

Enhanced type 1 immunity after secondary viral challenge in mice primed as neonates

The goal of infant immunization against viral infection is to develop protective long term memory responses. Priming neonatal mice with a low dose of Cas-Br-E murine leukemia virus (Cas) results in adult-like, type 1 protective responses. However, other studies suggest that Ag priming of neonates leads to an increase in type 2 secondary responses even when primary responses were type 1. We assessed whether type 1 CD8+ T cell-mediated responses developed in murine neonates are maintained after secondary challenge with Cas in adulthood. Despite the induction of significant anti-viral CD8+-mediated cytotoxic T lymphocyte and IFN-gamma responses, initial neonatal priming led to a lower frequency of virus-specific T cells compared with adult priming. Adult frequencies were reached in mice primed as neonates only after secondary challenge in adulthood. A nonspecific and transient CD4+-mediated IL-4 response was present in all groups after secondary challenge with Cas or medium, indicating that this rise in type 2 cytokine production was not unique to mice that had been primed as neonates. Rather, type 1 anti-viral memory CD8+ T cell responses developed in neonatal mice are stable, protective, and enhanced after secondary challenge.     

Distinct, cross-reactive epitope specificities of CD8 T cell responses are induced by natural hepatitis B surface antigen variants of different hepatitis B virus genotypes

We investigated the specific and cross-reactive CD8 T cell immunity to three natural variants (of different geno/serotype) of the small hepatitis B surface Ag (or S protein). The D(d)-binding variants of the S(201-209) epitope showed different immunogenicity. The loss of the consensus C-terminal (P9) anchor abrogated its immunogenicity. In contrast, a conservative (serine vs asparagine) exchange at P7 primed cross-reactive CD8 T cells that preferentially recognized the priming variant. Cross-reactive CD8 T cell responses to a variant could be primed in mice tolerant to an alternative variant of the D(d)-binding S(201-209) peptide. Loss of the C-terminal (P10) anchor in S(185-194) eliminated its immunogenicity in HLA-A*0201(A2)-transgenic mice but two conservative exchanges (leucine vs valine in P2, and leucine vs isoleucine in P6) in S(208-216) generated cross-reactive CD8 T cell responses with strong preference for the priming variant. Similar cross-reactive recognition of variant envelope epitopes were also found in S(208-216)-specific CD8 T cells from hepatitis B virus (HBV)-infected patients. Distinct CD8 T cell populations cross-reactive to natural variants of class I-restricted HBV epitopes can be primed by vaccination (of mice) or natural infection (of humans), and they may play a role in the "spontaneous remission" or the specific immunotherapy of chronic HBV infection.     

CD8 T cell expansion and memory differentiation are facilitated by simultaneous and sustained exposure to antigenic and inflammatory milieu

Understanding the factors contributing to the generation of immune memory is important for rational vaccine design. In this study, we addressed the individual and combined roles of Ag and inflammation in sustaining the ability of primed CD8 T cells to clonally expand and differentiate into memory cells. We transferred CD8 T cells that were primed for a brief period into naive mice, mice infected with a pathogen not carrying the specific Ag (inflammation only), mice infected with a pathogen carrying the donor cell-specific Ag (inflammation plus Ag), or into mice exposed to soluble Ag (Ag only). We found that the donor CD8 T cells continued to proliferate in all the four conditions, but their ability to clonally expand and differentiate into memory cells was approximately 1000-fold higher when transferred into mice acutely infected with pathogen carrying the relevant Ag. Memory cells generated under conditions of sustained exposure to inflammation and Ag during the priming phase were superior in their ability to elicit recall responses on a per cell basis. Thus, simultaneous and sustained exposure of donor CD8 T cells to inflammatory and antigenic stimuli, following the initial priming phase, leads to the greatest expansion of CD8 T cells at the peak of the immune response and induces an optimal memory differentiation program. These results suggest that vaccination strategies should attempt to provide sustained exposure to Ag plus inflammation but not either alone following the initial priming.     

MHC class I allele dosage alters CD8 expression by intestinal intraepithelial lymphocytes

The development of TCR alphabeta(+), CD8alphabeta(+) intestinal intraepithelial lymphocytes (IEL) is dependent on MHC class I molecules expressed in the thymus, while some CD8alphaalpha(+) IEL may arise independently of MHC class I. We examined the influence of MHC I allele dosage on the development CD8(+) T cells in RAG 2(-/-) mice expressing the H-2D(b)-restricted transgenic TCR specific for the male, Smcy-derived H-Y Ag (H-Y TCR). IEL in male mice heterozygous for the restricting (H-2D(b)) and nonrestricting (H-2D(d)) MHC class I alleles (MHC F(1)) were composed of a mixture of CD8alphabeta(+) and CD8alphaalpha(+) T cells, while T cells in the spleen were mostly CD8alphabeta(+). This was unlike IEL in male mice homozygous for H-2D(b), which had predominantly CD8alphaalpha(+) IEL and few mostly CD8(-) T cells in the spleen. Our results demonstrate that deletion of CD8alphabeta(+) cells in H-Y TCR male mice is dependent on two copies of H-2D(b), whereas the generation of CD8alphaalpha(+) IEL requires only one copy. The existence of CD8alphabeta(+) and CD8alphaalpha(+) IEL in MHC F(1) mice suggests that their generation is not mutually exclusive in cells with identical TCR. Furthermore, our data imply that the level of the restricting MHC class I allele determines a threshold for conventional CD8alphabeta(+) T cell selection in the thymus of H-Y TCR-transgenic mice, whereas the development of CD8alphaalpha(+) IEL is dependent on, but less sensitive to, this MHC class I allele.     

Augmentation of suppressed antibody responses in mice during experimental Chagas' disease by T helper cells activated in a time-dependent mode of immunization

Mice infected with the protozoan parasite Trypanosoma cruzi, the causative agent of human Chagas' disease, develop immunosuppressed responses to heterologous antigens. Experiments were performed using infected mice in the acute stage of infection to assess immunoregulatory activities during induction of direct plaque-forming cells (DPFC) to sheep erythrocytes (SRBC), hapten-conjugated SRBC (TNP-SRBC), and horse erythrocytes (TNP-HRBC). Studies in vivo demonstrated that anti-SRBC responses were best enhanced when T. cruzi-infected mice were injected with primed T cells derived from normal or infected mice immunized four days previously. The presence of enhancing capacities for DPFC responses by T cells from T. cruzi-infected mice were also supported by experiments examining the hapten-carrier effect. Preimmunization of infected mice with SRBC or HRBC four days before injection of hapten-homologous (TNP-SRBC or TNP-HRBC) carrier resulted in markedly augmented anti-hapten antibody responses. These results show that functional help provided by T cells activated during priming and exposed to a challenge dose of antigen (SRBC) in a time-dependent mode can overcome the effect of immunosuppression in T. cruzi-infected mice.     

Augmentation of Suppressed Antibody Responses in Mice During Experimental Chagas'Disease by T Helper Cells Activated in a Time-Dependent Mode of Immunization

ABSTRACT. Mice infected with the protozoan parasite Trypanosoma cruzi , the causative agent of human Chagas'disease, develop immunosuppressed responses to heterologous antigens. Experiments were performed using infected mice in the acute stage of infection to assess immunoregulatory activities during induction of direct plaque-forming cells (DPFC) to sheep erythrocytes (SRBC), hapten-conjugated SRBC (TNP-SRBC), and horse erythrocytes (TNP-HRBC). Studies in vivo demonstrated that anti-SRBC responses were best enhanced when T. cruz -infected mice were injected with primed T cells derived from normal or infected mice immunized four days previously. The presence of enhancing capacities for DPFC responses by T cells from T. cruzi -infected mice were also supported by experiments examining the hapten-carrier effect. Preimmunization of infected mice with SRBC or HRBC four days before injection of hapten-homologous (TNP-SRBC or TNP-HRBC) carrier resulted in markedly augmented anti-hapten antibody responses. These results show that functional help provided by T cells activated during priming and exposed to a challenge dose of antigen (SRBC) in a time-dependent mode can overcome the effect of immunosuppression in T. cruzi -infected mice.     

NAD+ released during inflammation participates in T cell homeostasis by inducing ART2-mediated death of naive T cells in vivo

Mono ADP-ribosyltransferase 2 (ART2) is an ectoenzyme expressed on mouse T lymphocytes, which catalyze the transfer of ADP-ribose groups from NAD(+) onto several target proteins. In vitro, ADP-ribosylation by ART2 activates the P2X7 ATP receptor and is responsible for NAD(+)-induced T cell death (NICD). Yet, the origin of extracellular NAD(+) and the role of NICD in vivo remain elusive. In a model of acute inflammation induced by polyacrylamide beads, we demonstrate release of NAD(+) into exudates during the early phase of the inflammatory response. This leads to T cell depletion in the draining lymph nodes from wild-type and, more severely, from mice lacking the CD38 NAD(+) glycohydrolase, whereas no effect is observed in ART2-deficient animals. Intravenous injection of NAD(+) used to exacerbate NICD in vivo results in fast and dramatic ART2- and P2X7-dependent depletion of CD4+ and CD8+ T lymphocytes, which can affect up to 80% of peripheral T cells in CD38(-/-) mice. This affects mainly naive T cells as most cells surviving in vivo NAD+ treatment exhibit the phenotype of recently activated/memory cells. Consistently, treatment with NAD(+) abolishes primary Ab response to a T-dependent Ag in NICD-susceptible CD38(-/-) mice but has no effect on the secondary response when given several days after priming. Unexpectedly NAD+ treatment improves the response in their wild-type BALB/c counterparts. We propose that NAD(+) released during early inflammation facilitates the expansion of primed T cells, through ART2-driven death of resting cells, thus contributing to the dynamic regulation of T cell homeostasis.     

T cell-derived cytokines associated with pulmonary immune mechanisms in mice vaccinated with irradiated cercariae of Schistosoma mansoni.

In C57Bl/6 strain mice vaccinated with attenuated cercariae of Schistosoma mansoni, the major site of immune elimination of normal challenge parasites is the lungs. The immune effector mechanism involves formation of focal inflammatory responses; the abundance of CD4+ T cells and the activation of alveolar macrophages suggests a role for inflammatory cytokines. We report the profile of cytokines produced by cultures of leukocytes recovered by bronchoalveolar lavage (BAL) from the lungs of vaccinated and challenged mice. From 14 days after vaccination, BAL cultures contained infiltrating lymphocytes that produced abundant quantities of IFN-gamma and IL-3 on stimulation with larval Ag. Production declined from day 21 although the infiltrate of lymphocytes persisted. Challenge of vaccinated mice resulted in a second influx of IFN-gamma and IL-3-producing cells, earlier than after vaccination or in the appropriate controls. Ablation studies revealed that CD4+ T cells were essential for the production of IFN-gamma. The timing of cytokine production after vaccination, and challenge was coincident with the phases of macrophage activation previously reported. At no time could lymphocytes in BAL cultures be stimulated to proliferate with either larval Ag or mitogen, in contrast to splenocytes from the same mice. Furthermore, T cell growth factor activity was not detected in BAL cultures stimulated with Ag. We suggest that the lymphocytes recruited to the lungs are memory/effector cells. When Ag released from challenge schistosomula is presented to these cells, they respond by secreting cytokines that mediate the formation of cellular aggregates around the parasites, blocking their onward migration.     

Time-dependent mode of immunization augments suppressed antibody responses in spleen cell cultures from mice experimentally infected with Trypanosoma cruzi

Mice infected with Trypanosoma cruzi develop immunosuppressed responses to heterologous antigens. Experiments were performed using infected mice in the acute stage of infection to assess immunoregulatory activities during induction of direct plaque-forming cells (DPFC) to sheep erythrocytes (SRBC). After normal or infected mice were primed with SRBC, their spleen cells were restimulated 4 days later with SRBC in Mishell-Dutton cultures and found to mount hyperaugmented IgM anti-SRBC responses. It was also demonstrated that T-cells derived from normal mice primed in vivo 4 days previously with SRBC, and subsequently added to cultures of spleen cells from T. cruzi-infected mice, enhanced anti-SRBC DPFC responses in a dose-dependent fashion. These results show that functional help provided by T-cells activated during an in vivo priming and exposed to an in vitro challenge dose of antigen (SRBC) in a time-dependent mode can overcome the effect of immunosuppression in the spleen cell cultures from T. cruzi-infected mice.     

Studies on primed precursors of effector T cells involved in delayed-type hypersensitivity to sheep red blood cells in mice

The nature of primed precursor T cells (primed pre-TD), capable of differentiating into effector T cells (TD) that mediate delayed-type hypersensitivity (DTH), was investigated in B10 mice which were primed by intravenous (iv) injection of various doses of sheep red blood cells (SRBC). The presence of primed pre-TD was detected by the ability of T cells in the spleens from primed mice, which were treated in vitro with pertussis toxin and then transferred into naive recipient mice, to generate DTH in the recipient mice 14 days after transfer. The primed pre-TD were induced antigen specifically 1 day after mice were primed by iv injection of a suboptimal (10(3)), an optimal (10(5)), or supraoptimal (10(9)) dose of SRBC. They were replaced by TD 4 days after priming in optimally sensitized mice, while they were maintained without generating TD for at least 5 weeks after priming in mice primed with either a suboptimal or a supraoptimal dose of SRBC. They were L3T4-positive and dense cells, fractionated in the high-density layers on a discontinuous Percoll density gradient, and capable of transforming into less dense TD, fractionated in the low-density layers. These results indicate that primed pre-TD, which are induced by an antigen signal and then can be activated by a nonspecific stimulus, are present not only in responsive mice but also in unresponsive mice, suggesting that either the generation of TD from primed pre-TD or primed pre-TD alone is the decisive factor for either responsiveness or unresponsiveness.     

Listeriolysin O-deficient Listeria monocytogenes as a vaccine delivery vehicle: antigen-specific CD8 T cell priming and protective immunity

Strains of Listeria monocytogenes (LM) that are deficient in the virulence factor listeriolysin O (LLO) are highly attenuated and are thought not to elicit protective immunity. This failure has been attributed to the inability of the bacterium to enter the host cell cytosol and access MHC class I Ag processing machinery. We reexamined this issue using recombinant strains of LM that are deficient in LLO but express an additional CD8 T cell epitope derived from lymphocytic choriomeningitis virus. After infection with LLO-deficient strains, we find sizable priming of epitope-specific CD8 T cells and the development of a functional memory cell population. Mice primed with the LLO-deficient LM strain are equally resistant against high-dose challenge with virulent LM as mice primed with wild-type virulent bacteria and also resist heterologous challenge with lymphocytic choriomeningitis virus. Interestingly, priming with a low dose of LLO-deficient LM, which occurred in environment of reduced inflammation (IFN-gamma), allowed rapid amplification of Ag-specific CD8 T cells by booster immunization, despite an undetectable primary response. We conclude that the generation of protective immunity by LLO-deficient strains of LM does in fact occur and that this highly attenuated LM strain may be a useful platform for vaccine delivery.     

Modulation of CD103 expression on human colon carcinoma-specific CTL

Recent results have shown a correlation between survival and frequency of tumor-infiltrating T cells in colorectal cancer patients. However, the mechanisms controlling the ability of human T lymphocytes to infiltrate colon carcinoma remain unclear. Although, it is known that expression of the integrin CD103alpha(E)/beta(7) by intraepithelial lymphocytes controls the retention of lymphocytes in epithelial layers, very little is known about the expression of intestinal homing receptors in human T lymphocytes. In particular, it remains unknown whether expression of CD103/beta(7) by human colon cancer-specific T lymphocytes is controlled by recognition of tumor Ags and is imprinted during T cell priming, facilitating its expression during memory T cell activation. In this study, we demonstrate that expression of CD103/beta(7) in human colon carcinoma-specific CTL is synergistically enhanced by the simultaneous TGF-beta1 stimulation and Ag recognition. These results were confirmed by using a panel of human CTL clones. Finally, we show that priming of naive CD8(+) T cells in the presence of TGF-beta1 ensures up-regulation of CD103/beta(7) in recall responses, at concentrations of TGF-beta1 significantly lower than those required by memory T cells primed in the absence of TGF-beta1. These results indicate a role of TGF-beta1 during T cell priming in modulating expression of CD103/beta(7) and controlling retention of human memory CD8(+) T cells into tumor epithelium.     

CD8+ T cells are a biologically relevant source of macrophage inflammatory protein-1 alpha in vivo

Chemokines are small proteins that direct the migration of leukocytes to inflammatory foci. Many cell types, including macrophages, fibroblasts, endothelial cells, and lymphocytes, produce chemokines in vitro, but biologically relevant sources of chemokines in vivo have not been well characterized. To investigate the pertinent sources of macrophage inflammatory protein-1 alpha (MIP-1 alpha) in vivo, we used MIP-1 alpha-deficient (MIP-1 alpha-/-) mice as donors and as recipients in adoptive transfer experiments after a lethal infection with Listeria monocytogenes (LM). Unexpectedly, we found that the production of MIP-1 alpha by CD8+ T cells was critical in this system, as the cells from MIP-1 alpha-/- mice primed with LM were significantly less effective in protecting naive mice against a lethal infection by LM than were the CD8+ T cells from wild-type (wt) mice. This requirement for donor T cell production of MIP-1 alpha was confirmed by the observation that wt donor T cells do not mediate protection when coadministered with an anti-MIP-1 alpha polyclonal antiserum. Production of MIP-1 alpha by the recipient mice was not required for protection, because wt and MIP-1 alpha-/- recipients were equally well protected by wt T cells. A 2- to 3-fold decrease in the number of transferred lymphocytes was seen in the spleens of mice receiving T cells from MIP-1 alpha-/- mice compared with those receiving wt T cells. In addition, CD8+ T cells from MIP-1 alpha-/- mice had a reduced ability to kill LM-infected target cells in vitro. These findings demonstrate that T cell production of MIP-1 alpha is required for clearance of an intracellular pathogen in vivo.     

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.     

Priming MHC-I-restricted cytotoxic T lymphocyte responses to exogenous hepatitis B surface antigen is CD4+ T cell dependent.

MHC-I (Ld)-restricted, S28-39-specific CTL responses are efficiently primed in H-2d BALB/c mice injected with low doses of native hepatitis B surface Ag (HBsAg) lipoprotein particles without adjuvants. Priming of this CTL response by exogenous HBsAg required CD4+ T cell "help" and IL-12: this CTL response could be neither induced in mice depleted of CD4+ T cells by in vivo Ab treatment, nor in (CD4+ T cell-competent or CD4+ T cell-depleted) IL-12-unresponsive STAT4-/- knockout BALB/c mice. Codelivery of oligonucleotides (ODN) with immunostimulating CpG sequences (ISS) with exogenous HBsAg reconstituted the CTL response to exogenous HBsAg in CD4+ T cell-depleted normal mice and in CD4+ T cell-competent and CD4+ T cell-depleted STAT4-/- BALB/c mice. Injection (by different routes) of "naked" pCI/S plasmid DNA encoding HBsAg into IL-12-responsive or -unresponsive BALB/c mice efficiently primed the MHC-I-restricted, HBsAg-specific CTL response. CTL priming was not detectable when CD4+ T cell-depleted animals were subjected to genetic immunization. In vivo priming of the well-characterized CD8+ CTL response to HBsAg in "high responder" BALB/c mice either by exogenous surface lipoprotein particles or by DNA vaccination is thus CD4+ T cell dependent. CTL priming by exogenous HBsAg, but not by genetic immunization, is IL-12 dependent. The dependence of CTL priming by exogenous HBsAg on CD4+ T cells can be overcome by codelivering ODN with ISS motifs, and this "adjuvants effect" operates efficiently in IL-12-unresponsive mice. The data characterize a feature of the adjuvant effect of ISS-containing ODN on CTL priming that may be of major interest for the design of CTL-stimulating vaccines with efficacy in immunodeficiency conditions.