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International audience; Langerhans cells (LCs) constitute a subset of dendritic cells (DCs) that express the lectin langerin and that reside in their immature state in epidermis. Paradoxically, in mice permitting diphtheria toxin (DT)-mediated ablation of LCs, epidermal LCs reappeared with kinetics that lagged behind that of their putative progeny found in lymph nodes (LNs). Using bone marrow (BM) chimeras, we showed that a major fraction of the langerin(+), skin-derived DCs found in LNs originates from a developmental pathway that is independent from that of epidermal LCs. This pathway, the existence of which was unexpected, originates in the dermis and gives rise to langerin(+) dermal DCs (DDCs) that should not be confused with epidermal LCs en route to LNs. It explains that after DT treatment, some langerin(+), skin-derived DCs reappear in LNs long before LC-derived DCs. Using CD45 expression and BrdU-labeling kinetics, both LCs and langerin(+) DDCs were found to coexist in wild-type mice. Moreover, DT-mediated ablation of epidermal LCs opened otherwise filled niches and permitted repopulation of adult noninflammatory epidermis with BM-derived LCs. Our results stress that the langerin(+) DC network is more complex than originally thought and have implications for the development of transcutaneous vaccines and the improvement of humanized mouse models.

OBJECTIVE: CD4(+)CD25(+) regulatory T lymphocytes (Treg) have been initially shown to prevent organ-specific autoimmunity. It is now accepted that Treg homeostasis depends in part on the peripheral conversion of na? CD4(+)CD25(-) T cells. This conversion implicates acquisition of the Treg-specific markers, forkhead winged helix protein 3 (Foxp3), after CD28 costimulation. Because natural killer cells (NK) are critical for efficient cytotoxic T-cell priming and TH1 polarization, we investigated their role in Foxp3 induction in CD4(+) T lymphocytes. MATERIALS AND METHODS: Human CD4(+)CD25(-) T lymphocytes were activated in vitro by CD28 costimulation in the presence of interleukin-2-activated NK. Three days after initial activation, Foxp3 protein and RNA expression were determined by flow cytometry and reverse transcription polymerase chain reaction. In vivo influence of activated NK on Foxp3 expression was studied in an adoptive transfer model of CD45.2(+) CD4(+)CD25(-) lymphocytes into CD45.1(+) mice. RESULTS: Interleukin-2-activated NK decreased Treg conversion of adoptively transferred murine CD4(+)CD25(-) T cells in vivo. Likewise, human-activated NK, but not resting NK, decreased CD28-driven Foxp3 expression in CD4(+)CD25(-) T lymphocytes, while at the same time increasing proliferation and interferon-gamma (IFN-gamma) production. Neutralization of IFN-gamma partially restored Treg conversion and prevented TH1 polarization after CD28 costimulation. CONCLUSION: The current study suggests that activated NK interfere with CD28-mediated Foxp3 expression in CD4(+)CD25(-) T lymphocytes. Our experiments further underline a molecular interaction between IFN-gamma and Foxp3 downstream of CD28 signaling. Together, these results demonstrate that activated NK play a critical role at the initiation step of immune responses by modulating peripheral Treg differentiation.

Recognition by T cells of their ligands at the surface of antigen-presenting cells (APCs) leads to T cell activation, polarization of the T cell toward the APC, and formation of an immune synapse. Using ZAP-70-deficient T cells expressing zeta-GFP, we show that ZAP-70 signaling drives the TCR-dependent reorientation of the microtubule-organizing center thus leading to relocation of a zeta-GFP(+) intracellular compartment close to the APC. ZAP-70 is also necessary to supply the synapse with the signaling molecules PKC-theta and LAT. In contrast, ZAP-70 is not required for clustering of zeta-GFP and CD2 or exclusion of CD45 and CD43 from the synapse. These data show that ZAP-70-dependent signaling is required for formation of a functional immune synapse.

International audience; It has recently been suggested that the percentage of smudge cells on blood smears from patients with chronic lymphocytic leukemia (CLL) could predict overall survival. However, smudge cells are a cytological artifact influenced by multiple physical factors not related to CLL. To identify simple parameters reflecting CLL cell fragility, we studied CD45 expression in a series of 66 patients with Binet stage A CLL. Decreased CD45 expression was specific for CLL cells when compared to 44 patients with a leukemic phase of B-cell non Hodgkin lymphoma and 42 control B-cells. CD45 expression was markedly decreased for all patients with CLL with high percentages of smudge cells. CLL cells with the lowest CD45 expression were the most sensitive to osmotic shock. Very low levels of CD45 expression were significantly associated with lack of CD38 expression, absence of trisomy 12, and with increased treatment free survival time. Altogether, these results demonstrate that low levels of CD45 expression are specific to CLL cells and reflect cell fragility, suggesting that this is an important intrinsic biological feature that determines disease course.

Polyelectrolyte multilayer (PEMs) films made of poly(allylamine hydrochloride) (PAH) as polycation and poly(styrene sulfonate) (PSS) as polyanion, with a PAH ending layer, can be used as a coating in order to improve the anti-thrombogenicity and patency of vascular grafts in vascular engineering field. They induce strong adhesion of mature endothelial cells on glass, expanded polytetrafluoroethylene and cryopreserved arteries. Despite their outstanding effect on mature and progenitor endothelial cells, PEMs ending with PAH showed a poor outcome on Wharton's jelly mesenchymal stem cells (WJ-MSCs) culture.The aim of this work was to examine the influence of the ending charge of PEMs on WJ-MSCs behavior.WJ-MSCs amplified until the 3rd passage were seeded and cultured on (PAH-PSS)3-PAH and on (PAH-PSS)4 coated glass for 10 days. Stem cell phenotype was checked by flow cytometry and cell morphology was followed by bright field microscopy.Flow cytometry analysis showed that WJ-MSCs were positive for MSC's markers CD73, CD90 and CD105 and negative for hematopoietic markers CD34 and CD45. Light microscopy showed development of nodule-like structures after 10 days of culture on (PAH-PSS)3-PAH, which resulted in a disturbance of cell monolayer. Whereas WJ-MSCs cultured on (PAH-PSS)4 ending with PSS showed a normal cell growth like on collagen and reached confluence after 10 days.The culture surface seems to have a determining role in WJ-MSC's "spatial" behavior, which could be considered in the field of tissue engineering.

International audience; Inflammation-mediated neurodegeneration occurs in the acute and the chronic phases of multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Classically activated (M1) microglia are key players mediating this process. Here, we identified Galectin-1 (Gal1), an endogenous glycan-binding protein, as a pivotal regulator of M1 microglial activation that targets the activation of p38MAPK-, CREB-, and NF-κB-dependent signaling pathways and hierarchically suppresses downstream proinflammatory mediators, such as iNOS, TNF, and CCL2. Gal1 bound to core 2 O-glycans on CD45, favoring retention of this glycoprotein on the microglial cell surface and augmenting its phosphatase activity and inhibitory function. Gal1 was highly expressed in the acute phase of EAE, and its targeted deletion resulted in pronounced inflammation-induced neurodegeneration. Adoptive transfer of Gal1-secreting astrocytes or administration of recombinant Gal1 suppressed EAE through mechanisms involving microglial deactivation. Thus, Gal1-glycan interactions are essential in tempering microglial activation, brain inflammation, and neurodegeneration, with critical therapeutic implications for MS.

International audience; In this study, we explored the potential of human naive CD4(+) T cells to acquire regulatory properties upon stimulation. We demonstrated that, in vitro, pre-activated naive CD4(+)CD25(-)CD45RA(+) T cells could become anergic and suppressive CD4(+)CD25(+) T cells upon lower intensity TCR stimulation. These CD4(+)CD25(+) T cells generated in vitro potently suppress the proliferation of allogenic CD4(+)CD25(-) T cells independently of cytokines and in a contact-dependent manner. Our data indicate that expression of Foxp3 is not necessary to induce the suppressive T cell activity. We demonstrate that these CD4(+)CD25(+) T cells are unresponsive upon re-stimulation and that their suppressive activity is transient. However, we showed that the anergy and the suppressive function could be reversed by increasing the stimulus and their level of activation. We concluded from our data that these anergy and suppressive activities are related to a fine tuning of TCR activation threshold.

International audience; Langerin is a C-type lectin receptor that recognizes glycosylated patterns on pathogens. Langerin is used to identify human and mouse epidermal Langerhans cells (LCs), as well as migratory LCs in the dermis and the skin draining lymph nodes (DLNs). Using a mouse model that allows conditional ablation of langerin(+) cells in vivo, together with congenic bone marrow chimeras and parabiotic mice as tools to differentiate LC- and blood-derived dendritic cells (DCs), we have revisited the origin of langerin(+) DCs in the skin DLNs. Our results show that in contrast to the current view, langerin(+)CD8(-) DCs in the skin DLNs do not derive exclusively from migratory LCs, but also include blood-borne langerin(+) DCs that transit through the dermis before reaching the DLN. The recruitment of circulating langerin(+) DCs to the skin is dependent on endothelial selectins and CCR2, whereas their recruitment to the skin DLNs requires CCR7 and is independent of CD62L. We also show that circulating langerin(+) DCs patrol the dermis in the steady state and migrate to the skin DLNs charged with skin antigens. We propose that this is an important and previously unappreciated element of immunosurveillance that needs to be taken into account in the design of novel vaccine strategies.

SummaryWe determined the number and functional status of CD4+CD25high regulatory T cells (Treg) in blood samples from patients with metastatic carcinoma, and evaluated their sensitivity to a single intravenous infusion of cyclophosphamide. Treg numbers were significantly higher in 49 patients with metastatic cancer (9·2% of CD4+ T cells) compared to 24 healthy donors (7·1%). These cells expressed the transcription factor forkhead box P3 (FoxP3), glucocorticoid-induced tumour necrosis factor receptor family-related protein (GITR) and intracellular CD152, and demonstrated a suppressive activity in vitro against CD4+CD25– autologous proliferation. At a single intravenous infusion, cyclophosphamide failed, in association with a non-specific immunotherapy by intratumoral bacille Calmette–Guérin (BCG), to modulate significantly Treg numbers or function. Metastatic cancer is associated with an expansion of peripheral blood CD4+CD25highFoxP3+GITR+CD152+Treg cells whose immunosuppressive properties do not differ from those of healthy subjects. Moreover, cyclophosphamide administration may not represent an optimal therapy to eliminate Treg, which further underlines the need to identify specific agents that would selectively deplete these cells.

We have recently described a CD19– B220+CD117low bone marrow subpopulation with B, T, and myeloid developmental potential, which we have called “early progenitors with lymphoid and myeloid potential” or EPLM. These cells also expressed Fms-like tyrosine kinase 3, Flt3, or CD135. Treatment of mice with the corresponding ligand, Flt3L, showed a 50-fold increase in EPLM. In addition to the expected increase in dendritic cell numbers, Flt3L treatment had a reversible inhibitory effect on B lymphopoiesis. Limiting dilution analysis of sorted EPLM from Flt3L-treated mice showed that B-lymphocyte progenitor activity was reduced 20-fold, but that myeloid and T-cell progenitor activity was largely preserved. EPLM from treated mice transiently reconstituted the thymus and bone marrow of recipient mice, generating cohorts of functional T and B cells in peripheral lymphoid organs. Thus, Flt3L treatment results in a dramatic increase in a novel bone marrow cell with lymphoid and myeloid progenitor activity.

International audience; OBJECTIVES: Humoral and cellular immune responses are likely to play a key role for the clearance or persistence and progression of high risk (HR) HPV-associated cervical lesions. Although there are many studies describing the systemic T-cell responses to HPV16 and 18 proteins, few data are available regarding the cellular mucosal immune responses. We used immunohistochemistry to characterize populations of T-immune cells (CD4+, CD8+, CD45RO+) in HR-HPV-infected precancerous and cancerous lesions of the uterine cervix. METHODS: Four biopsies from normal cervix, 9 CIN1 which have regressed (rCIN), 5 CIN1 which have progressed (pCIN) to high grade lesions, 13 CIN3 and 11 invasive carcinomas were included. All dysplasias and carcinomas were HR-HPV-positive and low-risk-HPV-negative. They were stained with monoclonal antibodies specific for CD4, CD8 and CD45RO and examined by microscopy. STATISTICAL ANALYSIS: The Kruskal-Wallis test and the Siegel's and Castelan's method were used. RESULTS.: CD4+ cells predominated in regressing CIN1 both within the stroma and the epithelium with the highest CD4+/CD8+ ratio compared with pCIN1, CIN3 and invasive carcinoma. At the exception of CD45RO+ cells, T cells were detected with similar frequencies in both pCIN1 and CIN3. However, in 7 out of 10 CIN3, CD4+ and CD8+ cells were visible as organized lymphoid follicle structure. The CD8+ and CD45RO+ cells far exceeded the CD4+ cells in invasive cancers. CONCLUSIONS: Density and distribution of immune T cells depend on the malignant potential of HR-HPV lesions. These results suggest that the studied lymphocyte subsets have an important role to fulfil during the natural history of HR-HPV-associated lesions.

OBJECTIVE: We recently identified in the mouse bone marrow a B-lymphoid/myeloid B220+ CD11b+ progenitor population. This population is accumulated in the osteopetrotic oc/oc mouse, which suggests that it could be controlled by bone marrow factors whose expression varies in this pathologic bone environment. Among the possible factors, interleukin (IL)-7 is involved in the control of B lymphopoiesis and osteoclastogenesis. Therefore, we hypothesized that IL-7 could regulate the accumulation of the B220+ CD11b+ population in oc/oc mice. METHODS: B220+ CD11b+ cells sorted from oc/oc mice were treated with IL-7 and their phenotype was analyzed by flow cytometry and real-time reverse transcriptase polymerase chain reaction (RT-PCR). In vivo, IL-7 was injected in oc/oc mice, and B220+ CD11b+ and B cells, as well as B-cell proliferation and apoptosis, were analyzed by flow cytometry. The expression of B lymphopoiesis and myelopoiesis markers was analyzed by real-time RT-PCR. RESULTS: In vitro, IL-7 induced the differentiation of B220+ CD11b+ cells into B lymphocytes through the induction of Pax5 and the inhibition of myeloid markers. In vivo, IL-7 injections in oc/oc mice induced a decrease of the B220+ CD11b+ population and the partial restoration of B-cell population, which was reduced in oc/oc mice. In parallel, upon IL-7 injections, Pax5 expression was induced in B220+ cells and B-cell apoptosis was reduced. CONCLUSIONS: Our results demonstrate that IL-7 injection can partially rescue B lymphopoiesis in oc/oc mice through the engagement of the B220+ CD11b+ population in the B-lymphoid pathway. Therefore, IL-7 delivery could represent a new therapeutic perspective to circumvent the lymphopenia observed in infantile malignant osteopetrosis patients.