Sorting of Leishmania-bearing dendritic cells reveals subtle parasite-induced modulation of host-cell gene expression.

Once in the mouse skin, Leishmania (L) amazonensis amastigotes are hosted by professional mononuclear phagocytes such as dendritic cells (DCs). When monitored after parasite inoculation, the frequency of amastigote-hosting DCs is very low (<1%) in both the skin and skin-draining lymph nodes. Therefore, we designed and validated an efficient procedure to purify live amastigotes-hosting DCs with the objective to facilitate quantitative and qualitative analysis of such rare cells. To this end, a L. amazonensis transgenic parasite expressing DsRed2 fluorescent protein was generated and added to mouse bone marrow-derived DC cultures. Then, a high speed sorting procedure, performed in BSL-2 containment, was setup to pick out only DCs hosting live amastigotes. This study reveals, for the first time, a unique transcript pattern from sorted live amastigotes-hosting DCs that would have been undetectable in unsorted samples. It was indeed possible to highlight a significant and coordinated up-regulation of L-arginine transporter and arginase2 transcripts in Leishmania-hosting DCs compared to un-parasitized DCs. These results indicate that arginine catabolism for polyamine generation is dominating over L-arginine catabolism for NO generation. In conclusion, this approach provides a powerful method for further characterisation, of amastigote-hosting DCs in the skin and the skin-draining lymph nodes.

Mycobacterium bovis bacillus Calmette-Guérin killed by extended freeze-drying targets plasmacytoid dendritic cells to regulate lung inflammation.

We have previously shown that bacillus Calmette-Guérin (BCG) inactivated by extended freeze-drying (EFD) reduces airway hyperresponsiveness, whereas live and heat-killed BCG fail to do so. However, the cells involved in the protective effect and the signaling and transcriptional networks that could reprogram T cell commitment after EFD BCG treatment remained to be elucidated. We investigated whether EFD BCG targets plasmacytoid dendritic cells (pDCs) potentially involved in the polarization of regulatory T cells (Tregs) and the transcriptional factors that regulate allergic inflammation. OVA-sensitized mice were s.c. injected with EFD, live, or heat-killed BCG. We analyzed after the injection of the various BCG preparations: 1) pDCs recruited in the draining lymph nodes (day 4); 2) transcription factors involved in inflammation and T cell commitment in spleen and lungs after OVA challenge (day 28). Airway hyperresponsiveness and transcription factors were determined after in vivo depletion of pDCs or Tregs in EFD BCG-treated and OVA-challenged mice. EFD BCG reduced inflammation via the recruitment of pDCs polarizing the differentiation of naive CD4+ T lymphocytes into Tregs. In vivo, pDC or Treg depletion at the time of EFD BCG treatment abrogated the protection against inflammation. EFD BCG treatment upregulated Forkhead-winged helix transcription factor (Treg signature) and downregulated GATA-3 and RORgammat (Th2 and Th17 signatures) more efficiently than live and heat-killed BCG. Moreover, only EFD BCG enhanced peroxisome proliferator-activated receptor gamma expression and blocked NF-kappaB activation, cyclooxygenase expression, and p38 MAPK phosphorylation. EFD BCG reduced allergic inflammation by recruiting pDCs that promoted Tregs; EFD BCG acted as a peroxisome proliferator-activated receptor gamma agonist and thus could be used in asthma and other inflammatory diseases.

Resting regulatory CD4 T cells: a site of HIV persistence in patients on long-term effective antiretroviral therapy.

BACKGROUND: In HIV-infected patients on long-term HAART, virus persistence in resting long-lived CD4 T cells is a major barrier to curing the infection. Cell quiescence, by favouring HIV latency, reduces the risk of recognition and cell destruction by cytotoxic lymphocytes. Several cell-activation-based approaches have been proposed to disrupt cell quiescence and then virus latency, but these approaches have not eradicated the virus. CD4+CD25+ regulatory T cells (Tregs) are a CD4+ T-cell subset with particular activation properties. We investigated the role of these cells in virus persistence in patients on long-term HAART. METHODOLOGY/PRINCIPAL FINDINGS: We found evidence of infection of resting Tregs (HLADR(-)CD69(-)CD25(hi)FoxP3+CD4+ T cells) purified from patients on prolonged HAART. HIV DNA harbouring cells appear more abundant in the Treg subset than in non-Tregs. The half-life of the Treg reservoir was estimated at 20 months. Since Tregs from patients on prolonged HAART showed hyporesponsiveness to cell activation and inhibition of HIV-specific cytotoxic T lymphocyte-related functions upon activation, therapeutics targeting cell quiescence to induce virus expression may not be appropriate for purging the Treg reservoir. CONCLUSIONS: Our results identify Tregs as a particular compartment within the latent reservoir that may require a specific approach for its purging.

Oral dendritic cells mediate antigen-specific tolerance by stimulating TH1 and regulatory CD4+ T cells.

BACKGROUND: A detailed characterization of oral antigen-presenting cells is critical to improve second-generation sublingual allergy vaccines. OBJECTIVE: To characterize oral dendritic cells (DCs) within lingual and buccal tissues from BALB/c mice with respect to their surface phenotype, distribution, and capacity to polarize CD4(+) T-cell responses. METHODS: In situ analysis of oral DCs was performed by immunohistology. Purified DCs were tested in vitro for their capacity to capture, process, and present the ovalbumin antigen to naive CD4(+) T cells. In vivo priming of ovalbumin-specific T cells adoptively transferred to BALB/c mice was analyzed by cytofluorometry in cervical lymph nodes after sublingual administration of mucoadhesive ovalbumin. RESULTS: Three subsets of oral DCs with a distinct tissue distribution were identified: (1) a minor subset of CD207(+) Langerhans cells located in the mucosa itself, (2) a major subpopulation of CD11b(+)CD11c(-) and CD11b(+)CD11c(+) myeloid DCs at the mucosal/submucosal interface, and (3) B220(+)120G8(+) plasmacytoid DCs found in submucosal tissues. Purified myeloid and plasmacytoid oral DCs capture and process the antigen efficiently and are programmed to elicit IFN-gamma and/or IL-10 production together with a suppressive function in naive CD4(+) T cells. Targeting the ovalbumin antigen to oral DCs in vivo by using mucoadhesive particles establishes tolerance in the absence of cell depletion through the stimulation of IFN-gamma and IL-10-producing CD4(+) regulatory T cells in cervical lymph nodes. CONCLUSION: The oral immune system is composed of various subsets of tolerogenic DCs organized in a compartmentalized manner and programmed to induce T(H)1/regulatory T-cell responses.

Plasmacytoid dendritic cells migrate in afferent skin lymph.

Conventional dendritic cells enter lymph nodes by migrating from peripheral tissues via the lymphatic route, whereas plasmacytoid dendritic cells (pDC), also called IFN-producing cells (IPC), are described to gain nodes from blood via the high endothelial venules. We demonstrate here that IPC/pDC migrate in the afferent lymph of two large mammals. In sheep, injection of type A CpG oligodinucleotide (ODN) induced lymph cells to produce type I IFN. Furthermore, low-density lymph cells collected at steady state produced type I IFN after stimulation with type A CpG ODN and enveloped viruses. Sheep lymph IPC were found within a minor B(neg)CD11c(neg) subset expressing CD45RB. They presented a plasmacytoid morphology, expressed high levels of TLR-7, TLR-9, and IFN regulatory factor 7 mRNA, induced IFN-gamma production in allogeneic CD4(pos) T cells, and differentiated into dendritic cell-like cells under viral stimulation, thus fulfilling criteria of bona fide pDC. In mini-pig, a CD4(pos)SIRP(pos) subset in afferent lymph cells, corresponding to pDC homologs, produced type I IFN after type A CpG-ODN triggering. Thus, pDC can link innate and acquired immunity by migrating from tissue to draining node via lymph, similarly to conventional dendritic cells.

Assessment of Bet v 1-specific CD4+ T cell responses in allergic and nonallergic individuals using MHC class II peptide tetramers.

In this study, we used HLA-DRB1*0101, DRB1*0401, and DRB1*1501 peptide tetramers combined with cytokine surface capture assays to characterize CD4(+) T cell responses against the immunodominant T cell epitope (peptide 141-155) from the major birch pollen allergen Bet v 1, in both healthy and allergic individuals. We could detect Bet v 1-specific T cells in the PBMC of 20 birch pollen allergic patients, but also in 9 of 9 healthy individuals tested. Analysis at a single-cell level revealed that allergen-specific CD4(+) T cells from healthy individuals secrete IFN-gamma and IL-10 in response to the allergen, whereas cells from allergic patients are bona fide Th2 cells (producing mostly IL-5, some IL-10, but no IFN-gamma), as corroborated by patterns of cytokines produced by T cell clones. A fraction of Bet v 1-specific cells isolated from healthy, but not allergic, individuals also expresses CTLA-4, glucocorticoid-induced TNF receptor, and Foxp 3, indicating that they represent regulatory T cells. In this model of seasonal exposure to allergen, we also demonstrate the tremendous dynamics of T cell responses in both allergic and nonallergic individuals during the peak pollen season, with an expansion of Bet v 1-specific precursors from 10(-6) to 10(-3) among circulating CD4(+) T lymphocytes. Allergy vaccines should be designed to recapitulate such naturally protective Th1/regulatory T cell responses observed in healthy individuals.

Similar functional activity of dendritic cells recruited to the mesenteric lymph nodes of newborn and adult mice after the rectal delivery of Mycobacterium bovis BCG.

BCG rectal administration to newborn and adult mice induced protective immune responses against tuberculosis. BCG reaches the sub-epithelial site and the draining mesenteric lymph nodes (MLNs), and dendritic cells (DC) could be recruited to these sites. Using polarized Caco-2 epithelial cells, we showed that BCG translocates epithelial cells to basolateral compartment. Delayed in newborn BALB/c mice, an important recruitment of CD11c+ DCs, was documented in the rectal lamina propria and the MLNs during the first two weeks after rectal BCG delivery. In MLNs, two major DC subtypes were observed: conventional DCs (cDCs) (B220-) and plasmacytoid DCs (pDCs) (B220+). CIRE, mouse DC-specific intracellular adhesion molecule 3 grabbing non-integrin (DC-SIGN) is predominantly expressed on pDCs and at a higher level on pDCs from the adult compared to newborn MLNs. cDCs with a higher capacity to induce the proliferation of naïve CD4+ T cells than pDCs, triggered CD4+ T cells to produce interferon-gamma whereas pDCs triggered them to release interleukin-10. Both DC subtypes equilibrates T cells as a source of microbicidal/microbiostatic signals and those acting as source of counter-inflammatory signals, preventing tissue damage and/or accelerating tissue repair. Thus, rectal delivery of BCG could be a safe and efficient route of vaccination against tuberculosis.

Synthesis, degradation, and antimicrobial properties of targeted macromolecular prodrugs of norfloxacin.

Long-term antibiotic treatment is required to cure tuberculosis. Targeted antibiotics should improve the efficacy of treatment by concentrating the drugs close to the bacteria. The aim of the present study was to synthesize targeted conjugates. For this purpose, we used mannose as a homing device to direct norfloxacin into macrophages. Dextran was used as the polymer bearing both mannose and norfloxacin. Using different peptide spacer arms to link norfloxacin to dextran, we demonstrated that norfloxacin acts as an antibiotic only when it is released in its native form. Also, targeting by using mannose as a homing device is required to achieve antimycobacterial activity in vivo. Thus, norfloxacin, which is inactive against mycobacteria in its native form in vivo, can be transformed into an active drug by targeting.

Bordetella bronchiseptica persists in the nasal cavities of mice and triggers early delivery of dendritic cells in the lymph nodes draining the lower and upper respiratory tract.

Early after the intranasal instillation of Bordetella bronchiseptica into mice, not only are mature dendritic leukocytes recovered from lung parenchyma and bronchoalveolar lavage fluid but their numbers are also increased in the mediastinal lymph nodes and the nasal mucosa-associated lymphoid tissue. Later during the infectious process, the bacteria persist mainly in the nasal cavity.

Dendritic cells recruited to the lung shortly after intranasal delivery of Mycobacterium bovis BCG drive the primary immune response towards a type 1 cytokine production.

We showed in a previous study that the intranasal (i.n) delivery of bacille Calmette-Guérin (BCG) to BP2 mice (H-2q) inhibits eosinophilia and bronchial hyperreactivity in a mouse model of asthma. The present work has been performed to characterize the leucocyte lineages recruited to the lungs of mice after i.n. delivery of BCG and potentially involved in the polarization of T lymphocytes. The different antigen-presenting cells (APC) recruited to bronchoalveolar lavage (BAL) and to lung tissue of mice shortly after the delivery of BCG were analysed in parallel as well as their capacity to drive the immune response towards a T helper type 1 cytokine production. Alveolar macrophages (AM) from the BAL were CD11c+, F4/80+ and CD11b-, and in the lung tissue two major populations of potential APC were detected: one CD11c-, F4/80+, CD11b+ and I-Aq- was identified as interstitial macrophages (IM) and a second expressing CD11c+ and I-Aq+ antigens, negative for CD11b and F4/80 markers as leucocytic dendritic cells (DC). Freshly isolated DC up-regulated CD11b and CD40 antigens after overnight culture, but remained negative for CD8alpha antigen, suggesting a myeloid origin. Lung DC which produced high amount of interleukin (IL)-12 were potent inducers of naive CD4+ T lymphocyte priming, as assessed by interferon-gamma (IFN-gamma) production by these naive CD4+ T cells. Lung explants recovered long term after BCG delivery produced sustained levels of IFN-gamma. Our results suggest that AM and particularly DC by secreting IL-12 shortly after BCG delivery induce the long-term persistence of IFN-gamma-secreting T cells percolating in BCG-loaded lung tissue.