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CpG-matured murine plasmacytoid dendritic cells are capable of in vivo priming of functional CD8 T cell responses to endogenous but not exogenous antigens.

Salio M, Palmowski MJ, Atzberger A, Hermans IF, Cerundolo V - J. Exp. Med. (2004)

Bottom Line: In vitro experiments have shown that upon maturation, human and murine PDCs develop into potent immunostimulatory cells; however, their ability to prime an immune response in vivo remains to be addressed.In contrast, immature PDCs are unable to prime antigen-specific CTLs.Our results underline the heterogeneity and plasticity of different antigen-presenting cells, and reveal an important role of mature PDCs in priming CD8 responses to endogenous antigens, in addition to their previously reported ability to modulate antiviral responses via type I IFN.

View Article: PubMed Central - PubMed

Affiliation: Cancer Research Tumor Immunology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headley Way, OX3 9DS Oxford, UK. mariolina.salio@imm.ox.ac.uk

ABSTRACT
Plasmacytoid dendritic cells (PDCs) are a unique leukocyte population capable of secreting high levels of type I interferon (IFN) in response to viruses and bacterial stimuli. In vitro experiments have shown that upon maturation, human and murine PDCs develop into potent immunostimulatory cells; however, their ability to prime an immune response in vivo remains to be addressed. We report that CpG-matured murine PDCs are capable of eliciting in naive mice antigen-specific CTLs against endogenous antigens as well as exogenous peptides, but not against an exogenous antigen. Type I IFN is not required for priming, as injection of CpG-matured PDCs into type I IFN receptor-deficient mice elicits functional CTL responses. Mature PDCs prime CTLs that secrete IFN-gamma and protect mice from a tumor challenge. In contrast, immature PDCs are unable to prime antigen-specific CTLs. However, mice injected with immature PDCs are fully responsive to secondary antigenic challenges, suggesting that PDCs have not induced long-lasting tolerance via anergic or regulatory T cells. Our results underline the heterogeneity and plasticity of different antigen-presenting cells, and reveal an important role of mature PDCs in priming CD8 responses to endogenous antigens, in addition to their previously reported ability to modulate antiviral responses via type I IFN.

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Direct presentation and not cross-priming accounts for expansion of UTY246–254-specific CTL. C57BL/6 mice were injected i.v. with the indicated numbers of male immature or CpG-matured BM-DCs (generated in FLT3-L). CTL responses were assessed in the blood by FACS® analysis using UTY246–254-H-2-Db tetramers 7 d after priming, and dot plot profiles for individual mice are shown. Only the mice injected with 106 BM-DCs showed secondary responses after boosting with vaccinia-UTY246–254 minigene (not depicted).
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fig6: Direct presentation and not cross-priming accounts for expansion of UTY246–254-specific CTL. C57BL/6 mice were injected i.v. with the indicated numbers of male immature or CpG-matured BM-DCs (generated in FLT3-L). CTL responses were assessed in the blood by FACS® analysis using UTY246–254-H-2-Db tetramers 7 d after priming, and dot plot profiles for individual mice are shown. Only the mice injected with 106 BM-DCs showed secondary responses after boosting with vaccinia-UTY246–254 minigene (not depicted).

Mentions: Priming of UTY246–254-specific CTLs by CpG-matured PDCs and MDCs could be due to direct presentation of the UTY246–254 peptide by the male APCs. Alternatively, proliferation of UTY246–254-specific CTLs could be due to uptake and presentation of male APC debris by resident female DCs, a mechanism known as cross-priming. Indeed, cross-priming has been shown to be effective for the generation of cytotoxic T cells, and it may be the dominant route for priming of some responses (30, 31). In vitro experiments showed that presentation of the UTY246–254 epitope is entirely TAP-dependent as UTY246–254-specific T cells did not recognize TAP-1–deficient male APCs (unpublished data). Therefore, we used TAP-1–deficient male BM-DCs as immunogens to distinguish between direct versus cross-presentation. Injection of as many as 106 male TAP-1−/− BM-DCs, either immature or CpG matured, failed to prime UTY246–254-specific CTLs in female C57BL/6 mice (Fig. 6). In contrast, control mice developed good responses after injection with 105 wild-type BM-DCs. After boosting with vaccinia-UTY246–254 minigene, only mice that had been primed with 106 male TAP-1−/− DC (i.e., 10 times more APCs than used in previous experiments) showed enhanced CTL responses (unpublished data). In agreement with the observation that UTY246–254-specific CTL responses cannot be efficiently generated upon priming by β-2m–deficient APCs (28), we conclude that the role of cross-priming in generating UTY246–254-specific CTLs in this system is marginal, and can only be appreciated when animals are injected with large numbers of APCs. Therefore, proliferation of UTY246–254-specific CTLs in our in vivo model can be accounted for by direct presentation of the endogenous antigen by the injected PDCs and MDCs.


CpG-matured murine plasmacytoid dendritic cells are capable of in vivo priming of functional CD8 T cell responses to endogenous but not exogenous antigens.

Salio M, Palmowski MJ, Atzberger A, Hermans IF, Cerundolo V - J. Exp. Med. (2004)

Direct presentation and not cross-priming accounts for expansion of UTY246–254-specific CTL. C57BL/6 mice were injected i.v. with the indicated numbers of male immature or CpG-matured BM-DCs (generated in FLT3-L). CTL responses were assessed in the blood by FACS® analysis using UTY246–254-H-2-Db tetramers 7 d after priming, and dot plot profiles for individual mice are shown. Only the mice injected with 106 BM-DCs showed secondary responses after boosting with vaccinia-UTY246–254 minigene (not depicted).
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2211835&req=5

fig6: Direct presentation and not cross-priming accounts for expansion of UTY246–254-specific CTL. C57BL/6 mice were injected i.v. with the indicated numbers of male immature or CpG-matured BM-DCs (generated in FLT3-L). CTL responses were assessed in the blood by FACS® analysis using UTY246–254-H-2-Db tetramers 7 d after priming, and dot plot profiles for individual mice are shown. Only the mice injected with 106 BM-DCs showed secondary responses after boosting with vaccinia-UTY246–254 minigene (not depicted).
Mentions: Priming of UTY246–254-specific CTLs by CpG-matured PDCs and MDCs could be due to direct presentation of the UTY246–254 peptide by the male APCs. Alternatively, proliferation of UTY246–254-specific CTLs could be due to uptake and presentation of male APC debris by resident female DCs, a mechanism known as cross-priming. Indeed, cross-priming has been shown to be effective for the generation of cytotoxic T cells, and it may be the dominant route for priming of some responses (30, 31). In vitro experiments showed that presentation of the UTY246–254 epitope is entirely TAP-dependent as UTY246–254-specific T cells did not recognize TAP-1–deficient male APCs (unpublished data). Therefore, we used TAP-1–deficient male BM-DCs as immunogens to distinguish between direct versus cross-presentation. Injection of as many as 106 male TAP-1−/− BM-DCs, either immature or CpG matured, failed to prime UTY246–254-specific CTLs in female C57BL/6 mice (Fig. 6). In contrast, control mice developed good responses after injection with 105 wild-type BM-DCs. After boosting with vaccinia-UTY246–254 minigene, only mice that had been primed with 106 male TAP-1−/− DC (i.e., 10 times more APCs than used in previous experiments) showed enhanced CTL responses (unpublished data). In agreement with the observation that UTY246–254-specific CTL responses cannot be efficiently generated upon priming by β-2m–deficient APCs (28), we conclude that the role of cross-priming in generating UTY246–254-specific CTLs in this system is marginal, and can only be appreciated when animals are injected with large numbers of APCs. Therefore, proliferation of UTY246–254-specific CTLs in our in vivo model can be accounted for by direct presentation of the endogenous antigen by the injected PDCs and MDCs.

Bottom Line: In vitro experiments have shown that upon maturation, human and murine PDCs develop into potent immunostimulatory cells; however, their ability to prime an immune response in vivo remains to be addressed.In contrast, immature PDCs are unable to prime antigen-specific CTLs.Our results underline the heterogeneity and plasticity of different antigen-presenting cells, and reveal an important role of mature PDCs in priming CD8 responses to endogenous antigens, in addition to their previously reported ability to modulate antiviral responses via type I IFN.

View Article: PubMed Central - PubMed

Affiliation: Cancer Research Tumor Immunology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headley Way, OX3 9DS Oxford, UK. mariolina.salio@imm.ox.ac.uk

ABSTRACT
Plasmacytoid dendritic cells (PDCs) are a unique leukocyte population capable of secreting high levels of type I interferon (IFN) in response to viruses and bacterial stimuli. In vitro experiments have shown that upon maturation, human and murine PDCs develop into potent immunostimulatory cells; however, their ability to prime an immune response in vivo remains to be addressed. We report that CpG-matured murine PDCs are capable of eliciting in naive mice antigen-specific CTLs against endogenous antigens as well as exogenous peptides, but not against an exogenous antigen. Type I IFN is not required for priming, as injection of CpG-matured PDCs into type I IFN receptor-deficient mice elicits functional CTL responses. Mature PDCs prime CTLs that secrete IFN-gamma and protect mice from a tumor challenge. In contrast, immature PDCs are unable to prime antigen-specific CTLs. However, mice injected with immature PDCs are fully responsive to secondary antigenic challenges, suggesting that PDCs have not induced long-lasting tolerance via anergic or regulatory T cells. Our results underline the heterogeneity and plasticity of different antigen-presenting cells, and reveal an important role of mature PDCs in priming CD8 responses to endogenous antigens, in addition to their previously reported ability to modulate antiviral responses via type I IFN.

Show MeSH
Related in: MedlinePlus