Distinct Dendritic Cells Subsets Research Articles

Pathogenesis of Allergic Airway Inflammation

Advances have been made in defining the mechanisms for the control of allergic airway inflammation in response to inhaled antigens. Several genes, including ADAM33, DPP10, PHF11, GPRA, TIM-1, PDE4D, OPN3, and ORMDL3, have been implicated in the pathogenesis and susceptibility to atopy and asthma. Growing evidence associates asthma with a systemic propensity for allergic T-helper type 2 cytokines. Disordered coagulation and fibrinolysis also exacerbate asthma symptoms. Balance among functionally distinct dendritic cell subsets contributes to the outcome of T-cell-mediated immunity. Allergen-specific T-regulatory cells play a pivotal role in the development of tolerance to allergens and immune suppression. The major emphasis on immunotherapy for asthma during the past decade has been to direct the immune response to a type 1 response, or immune tolerance. In this review, we discuss the current information on the pathogenesis of allergic airway inflammation and potential immunotherapy, which could be beneficial in the treatment of airway inflammation, allergy, and asthma.

Phagocytosis May Be a Regulatory Mechanism for Myeloid Dendritic Cells to Terminate Type 1 CD8+ T Cells.

Abstract 1654Poster Board I-680CD8+ cytotoxic T cells are often ‘exhausted' by programmed death-1 (PD-1) signaling, and subsequently the functions of these cells are terminated especially in a tumor environment or upon chronic HIV or HCV infection. Subsets of myeloid cells referred to as myeloid derived suppressor cells (MDSC) or regulatory dendritic cells (DCs) have been implicated in inducing exhaustion or termination of effector CD8+ T cells. To this end, we developed various myeloid-derived dendritic cell (DC) types in vitro from human CD14+ monocytes using M-CSF or GM-CSF in the presence of IL-4 with/without other cytokines, and characterized these DCs with respect to their capacity to induce PD-1 expression on and exhaustion of CD8+ T cells. We then assessed their impact on longevity of CD8+ T cells following coculture. Myeloid DCs developed in vitro with M-CSF and IL-4 for 5 days (referred to as M-DC) did not express ligand for PD-1 (PD-L1) nor did they induce PD-1 on CD8+ T cells. Thus, using M-DCs as starting cells, we sought determinant factors that could modulate M-DCs to express PD-L1 and thereby induce exhaustion of CD8+ T cells. In order to better monitor exhaustion processes, we incubated human peripheral CD8+ T cells for 5 days in the presence of IL-15, an important cytokine for maintaining viability, before coculture. M-DCs showed little impact on exhaustion or longevity of the CD8+ T cells. IL-10 converted M-DC into a distinct myeloid DC subset (referred to as M-DC/IL-10) with an ability to express PD-L1 as well as to induce PD-1 on cocultured CD8+ T cells. M-DC/IL-10 cells markedly suppressed proliferation of cocultured CD8+ T cells. M-DC/IL-10 cells were morphologically unique with many granules and filamentous structures around the cell periphery. These IL-10 effects on M-DC were completely abrogated in the presence of TNF-á. M-DC/IL-10 cells could be further differentiated into another myeloid DC subset in the presence of IFN-γ (referred to as M-DC/IL-10/IFN-γ) with an ability to express even higher levels of PD-L1 compared to M-DC/IL-10 cells. The most remarkable effect of M-DC/IL-10/IFN-γ cells on cocultured CD8+ T cells was a dramatic loss of CD8+ T cells. Light and confocal microscopic observations indicated that loss of CD8+ T cells was due to phagocytosis by M-DC/IL-10/IFN-γ cells. As IFN-γ, a type 1 cytokine which is induced in CD8+ T cells by IL-12 is essential for phagocytosis, we tested whether IL-12 treatment of CD8+ T cells could further enhance phagocytosis induced by M-DC/IL-10/IFN-γ cells. Indeed, IL-12 treatment greatly increased numbers of phagocytosed CD8+ T cells. In contrast, IL-4 treated CD8+ T cells became resistant to phagocytosis, suggesting IFN-γ producing (type1) CD8+ T cells may be primary target cells for the M-DC/IL-10 cells mediated phagocytosis. CD4+ T cells were not as susceptible as CD8+ T cells to phagocytosis. We failed to detect such phagocytic activity induced by prototype DCs generated with GM-CSF and IL-4. Phagocytic activity was not inhibited by various arginase-1 inhibitors suggesting that nitric oxide signaling may not mediate phagocytic activity. Neutralizing antibody to PD-L1 slightly but significantly lowered phagocytic activity suggesting that PD-L1/PD-1 interaction may be partially involved in this process. Myeloid DCs are thought to be immunogenic, actively inducing T cell immune responses. Our results demonstrate that myeloid DCs may play suppressive roles as well through induction of phagocytic activity, especially against IFN-γ producing CD8+ T cells. This may serve as a regulatory mechanism for type 1 CD8+ T cell immune responses in an IL-10 enriched microenvironment. DisclosuresNo relevant conflicts of interest to declare.

Haematopoietic stem cells in spleen have distinct differentiative potential for antigen presenting cells.

Dendritic cells (DC) are known to develop from macrophage dendritic progenitors (MDP) in bone marrow (BM), which give rise to conventional (c)DC and monocytes, both dominant antigen presenting cell (APC) subsets in spleen. This laboratory has however defined a distinct dendritic-like cell subset in spleen (L-DC), which can also be derived in long-term cultures of spleen. In line with the restricted in vitro development of only L-DC in these stromal cultures, we questioned whether self-renewing HSC or progenitors exist in spleen with restricted differentiative capacity for only L-DC. Neonatal spleen and BM were compared for their ability to reconstitute mice and to give rise to L-DC, as well as other splenic APC. Neonatal spleen cells were transplanted into allotype-distinct lethally irradiated hosts along with host-type competitor BM cells, and assayed over 8 to 51 weeks for haematopoietic reconstitution of L-DC and cDC subsets, along with other lymphoid and myeloid cells. In this study, neonatal spleen showed multilineage haematopoietic reconstitution in mouse chimeras, rather than specific or restricted ability to differentiate into L-DC. However, the representation of individual APC subsets was found to be unequal in chimeras partially reconstituted with donor cells, such that more donor-derived progeny were seen for L-DC than for myeloid and cDC subsets. The ability of HSC in spleen to develop into L-DC was indicated by a strong bias in the subset size of these cells over other splenic APC subsets. This type of evidence supports a model whereby spleen represents an important site for haematopoiesis of this distinct DC subset. The conditions under which haematopoiesis of L-DC occurs in spleen, or the progenitors involved, will require further investigation.

Harnessing Dendritic Cells to Generate Cancer Vaccines

Passive immunotherapy of cancer (i.e., transfer of T cells or antibodies) can lead to some objective clinical responses, thus demonstrating that the immune system can reject tumors. However, passive immunotherapy is not expected to yield memory T cells that might control tumor outgrowth. Active immunotherapy with dendritic cell (DC) vaccines has the potential to induce tumor-specific effector and memory T cells. Clinical trials testing first-generation DC vaccines pulsed with tumor antigens provided a proof-of-principle that therapeutic immunity can be elicited. Newer generation DC vaccines are built on the increased knowledge of the DC system, including the existence of distinct DC subsets and their plasticity all leading to the generation of distinct types of immunity. Rather than the quantity of IFN-gamma-secreting CD8(+) T cells, we should aim at generating high-quality, high-avidity, polyfunctional effector CD8(+) T cells able to reject tumors and long-lived memory CD8(+) T cells able to prevent relapse.

Probiotic Preparation VSL#3 Alters the Distribution and Phenotypes of Dendritic Cells within the Intestinal Mucosa in C57BL/10J Mice1–3

Probiotic nutrients have shown promise in therapy for the treatment of gastrointestinal inflammation, infection, and atopic disease. Intestinal dendritic cells (DC) play a critical role in shaping the intestinal immune response. In this study, we tested the effect of a probiotic preparation (VSL#3) on DC distribution and phenotypes within the intestinal mucosa using a lineage depletion-based flow cytometric analysis. In naïve C57BL/10J mice, intestinal mucosal DC were composed of plasmacytoid DC (pDC) and myeloid DC (mDC). The pDC were the dominant form in lamina propria and Peyer’s patches, whereas mDC were the prevailing type in the mesenteric lymph nodes. Additional characterization of pDC and mDC with flow cytometry revealed that they expressed heterogeneous phenotypes in the intestinal mucosa. In mice gavaged with the probiotic VSL#3 for 7 d, the proportion of pDC within the lamina propria was >60% lower, whereas the pDC subset in the mesenteric lymph nodes was more than 200% greater than in sham-treated controls (P < 0.01). Within pDC, the proportion of functionally unique CX3CR1+ DC was greater than in controls in both the lamina propria and the Peyer’s patches (P < 0.01). In contrast to pDC, the mDC number was greater than in controls in all intestinal lymphoid tissue compartments in VSL#3-treated mice (P < 0.01). In conclusion, this study suggests that phenotypically and functionally distinct DC subsets are localized to specific lymphoid tissues within the intestinal mucosa and that the VSL#3 probiotic nutritional supplement alters the distribution of the DC subsets within the intestinal mucosa. These changes may be important in the alteration of mucosal immunity following probiotic VSL#3 therapy.

Balancing inflammation and tolerance in vivo through dendritic cells by the commensal Candida albicans

We analyzed the contribution of intracellular signaling to the functional plasticity of dendritic cells (DCs) presenting Candida albicans, a human commensal associated with severe diseases. Distinct intracellular pathways were activated by recognition of different fungal morphotypes in distinct DC subsets and in Peyer's patches DCs. Inflammatory DCs initiated Th17/Th2 responses to yeasts through the adaptor myeloid differentiation factor-88 (MyD88), whereas tolerogenic DCs activate Th1/T regulatory cell (Treg) differentiation programs to hyphae involving Toll/IL-1 receptor domain-containing adaptor inducing IFN-beta (TRIF) as an intermediary of signaling. In addition, signal transducer and activator of transcription 3 (STAT3), affecting the balance between canonical and non-canonical activation of nuclear factor-kappaB (NF-κB) and 2,3 indoleamine dioxygenase (IDO), pivotally contributed to DC plasticity and functional specialization. As Candida-induced tolerogenic DCs ameliorated experimental colitis, our data qualify Candida as a commensal with immunoregulatory activity, resulting from the orchestrated usage of multiple, yet functionally distinct, receptor–signaling pathways in DCs. Ultimately, affecting the local Th17/Treg balance might likely be exploited by the fungus for either commensalism or pathogenicity.

Cytoplasmic Proteome and Secretome Profiles of Differently Stimulated Human Dendritic Cells

Dendritic cells (DCs), the most potent and specialized antigen-presenting cells, play a key role in the regulation of the adaptive immunity. Immature DCs were generated by in vitro culturing of peripheral blood monocytes and functionally activated with the classical pathogen-associated molecular pattern lipopolysaccharide (LPS). Alternative activation resulting in Th-2 polarization was induced with lipid oxidation products derived from 1-palmitoyl-2-arachidoyl-sn-glycerol-3-phosphorylcholin (OxPAPC). Tolerogenic cells were obtained by treating DCs with human rhinovirus (HRV). The aim of this study was the identification of proteome profiles related to the functionally different dendritic cell phenotypes. Cytoplasmic proteins were analyzed by shotgun proteomics resulting in the identification of 1690 proteins. While mature and alternatively activated DCs displayed highly distinct protein expression profiles, HRV-treated DCs showed minor proteome alterations. As DCs exert many specific functions via secretion, we investigated the secretomes by a combination of 2D-PAGE and shotgun proteomics. We successfully identified a broad variety of cytokines (e.g., GM-CSF, TNF-alpha, interleukin-1beta, 6, 12 beta, 28B and 29), chemokines (e.g., CCL3, 5, 8, 17, 18, 19, 24, CXCL1, 2, 9 and 10) and growth factors (growth/differentiation factor 8, C-type lectin domain family 11 member A). The relative composition of secretome profiles, although comprising much less proteins, was found to be much more affected by functional alteration of cells than the cytoplasmic protein composition. In conclusion, we demonstrate that functional distinct subsets of DCs display distinct proteome profiles which comprise biomarker candidates. These proteins may prove useful for the interpretation of complex clinical proteomics data.

Distinct subsets of human skin dendritic cells differ on their ability to initiate Th17 responses (90.24)

Abstract Activated human cutaneous dendritic cells (DCs) have the ability to initiate Th1 and Th2 immunity. However, whether human cutaneous DCs are capable of biasing pro-inflammatory Th17 responses remains little understood. Utilizing human skin explants composed by both epidermis and dermis or epidermal or dermal sheets to collect activated skin-migratory DCs (smiDCs), we demonstrated that smiDCs stimulate allogeneic naïve CD4+ T cells to differentiate simultaneously into two distinct effector Th17 and Th1 populations with ability of skin homing and inducing severe tissue damage. Of the two main myeloid DC populations resident in the skin, the subset of epidermal skin-migratory Langerhans cells (smiLCs) were capable of inducing Th17 responses. This effect depended on the combined effects of IL-15 and stabilized IL-6 trans-signaling of naïve CD4+ T cells. Purified skin-migratory DDCs did not synthesize IL-15 and were unable to bias Th17 responses however, they acquired the ability to bias Th17 cells in co-cultures with CD4+ T cells supplemented with IL-15 and stabilized IL-6. Overall, our data demonstrate that human cutaneous LCs induce Th17 responses by mechanisms different from those previously described for mouse DCs and human monocytes and highlight the need to target clinical treatments based on these variations. Supported by NIH grants: R01 CA100893 (ATL)

Interferon-α Differentially Affects Homeostasis of Human Plasmacytoid and Myeloid Dendritic Cells

Interferon-alpha (IFN-alpha) is widely used for the treatment of malignant and viral diseases. Conflicting results of IFN-alpha-mediated effects on dendritic cell (DC) homeostasis have been reported and its impact on human blood DC is largely unknown. We investigated the phenotypic, migratory, and allostimulatory activities of plasmacytoid DCs (PDCs) and myeloid DCs (MDCs) upon in vitro exposure to IFN-alpha without the addition of exogenous DC growth factors. IFN-alpha-exposed PDCs exhibited an increase in viability but showed an immature phenotype and a diminished allostimulatory potential. Furthermore, IFN-alpha-treated PDCs displayed a dramatically augmented expression of CD54 and CD62L as well as an increased migratory response to CC chemokine ligand (CCL)19, CXC chemokine ligand (CXCL)11, and CXCL12, suggesting an enhanced ability to migrate into peripheral lymph nodes through high endothelial venules. Myeloid DCs exposed to IFN-alpha exhibited a matured phenotype with an increased propensity to migrate toward lymph node chemokines, yet without gaining an enhanced allostimulatory capacity. Our results provide new insights into the differential immunomodulatory action of IFN-alpha on distinct human blood DC subsets and thus, may present translational significance.

Migratory and Lymphoid-Resident Dendritic Cells Cooperate to Efficiently Prime Naive CD4 T cells

To initiate an adaptive immune response, rare antigen-specific naive CD4(+) T cells must interact with equally rare dendritic cells (DCs) bearing cognate peptide-major histocompatibility complex (MHC) complexes. Lymph nodes (LNs) draining the site of antigen entry are populated by lymphoid-resident DCs as well as DCs that have immigrated from tissues, although the requirement for each population in initiating the T cell response remains unclear. Here, we show that antigen processing and presentation by both lymphoid-resident and migratory DCs was required for clonal selection and expansion of CD4(+) T cells after subcutaneous immunization. Early antigen presentation by lymphoid-resident DCs initiated activation and trapping of antigen-specific T cells in the draining LN, without sufficing for clonal expansion. Migratory DCs, however, interacted with the CD4(+) T cells retained in the LN to induce proliferation. Therefore, distinct DC subsets cooperate to alert and trap the appropriate cell and then license its expansion and differentiation.

Significant Decline of Peripheral Myeloid Dendritic Cells Following Multiple Trauma

Dendritic cells (DC) represent an important and integral part of the immune system and are potent initiators of inflammation. Two distinct subsets of DC have been identified: myeloid DC (MDC) and plasmacytoid DC (PDC), which differ widely in many respects. Despite the importance of the DC in the inflammatory response that occurs after severe multiple injury, there is a profound lack of information regarding the distribution and regulation of DC subtypes following multiple trauma. The main goal of this study was to assess whether the normal distribution of circulating DC subpopulations is altered during the first 5 d after multiple trauma. Sixty-three patients with multiple trauma (ISS 31 +/- 15 points) and 11 healthy volunteers (control group) were enrolled. Blood samples were taken on admission (D0) and daily for the following 5 d. The percentages of MDC and PDC were determined by flow cytometry. A significant decline of the MDC concentration was observable on days 3 to 5 after admission in comparison to the values obtained on the day of admission. The ratio of MDC to PDC decreased significantly (3-fold, P < 0.05). This reduction correlated significantly with changes observed in the plasma concentrations of IL-10 (r = 0.5; P < 0.05). Our data demonstrate that multiple trauma is followed by a marked change in the subpopulation composition of the DC compartment, and that these changes are inversely associated with enhanced IL-10 plasma concentrations. This imbalance in the DC compartment favoring PDC concentrations may contribute to the immunological alterations that are observed following multiple trauma.

Nuclear receptor signalling in dendritic cells connects lipids, the genome and immune function

Dendritic cells (DCs) are sentinels of the immune system and represent a heterogeneous cell population. The existence of distinct DC subsets is due to their inherent plasticity and to the changing microenvironment modulating their immunological properties. Numerous signalling pathways have impacts on DCs. It appears that besides cytokines/chemokines, lipid mediators also have profound effects on the immunogenicity of DCs. Some of these lipid mediators exert an effect through nuclear hormone receptors. Interestingly, more recent findings suggest that DCs are able to convert precursors to active hormones, ligands for nuclear receptors. Some of these DC-derived lipids, in particular retinoic acid (RA), have a central function in shaping T-cell development and effector functions. In this review, we summarize and highlight the function of a set of nuclear receptors (PPARγ, RA receptor, vitamin D receptor and glucocorticoid receptor) in DC biology. Defining the contribution of nuclear hormone receptor signalling in DCs can help one to understand the regulatory logic of lipid signalling and allow the exploitation of their potential for therapeutic intervention in various immunological diseases.

Identification of ITGA4/ITGB7 and ITGAE/ITGB7 Expressing Subsets of Decidual Dendritic-Like Cells Within Distinct Microdomains of the Pregnant Mouse Uterus1

Several leukocyte populations have been described within the pregnant mouse uterus, some of which express the integrin beta 7 (ITGB7). Here we demonstrate that the majority of the ITGB7(+) decidual leukocytes belong to the dendritic cell (DC) lineage. By multiparameter flow cytometric analysis we demonstrated the existence of three distinct DC subsets, characterized by differential expression of ITGA4/ITGB7 (formerly alpha4beta7-integrin) and ITGAE/ITGB7 (formerly alphaEbeta7-integrin). Importantly, the predominant DC subsets reside in distinct microdomains of the Day 9 pregnant mouse uterus. ITGAX(+) ITGAM(med) ITGA4/ITGB7(+) ITGAE(-) (formerly CD11c(+) CD11b(med) alpha4beta7(+) alphaE(-)) cells represent the majority of DCs in the vascular zone (VZ), whereas ITGAX(+) ITGAM(-) ITGAE/ITGB7(+) (formerly CD11c(+) CD11b(-) alphaEbeta7(+)) DCs are mainly located in the lower central decidua basalis (cDB) and the underlying myometrium. A population of ITGAX(+) ITGAM(low) DCs lacking ITGB7 are restricted to the cDB. Confocal microscopy studies show direct contact of VZ DCs with uterine natural killer (uNK) cells, suggesting a functional relationship between both cell populations. Collectively, our data identify three phenotypically distinct DC subsets residing in distinct microdomains of the uterus. The differential expression of ITGA4/ITGB7 and ITGAE/ITGB7 suggests distinct functional roles of the different DC subsets during early pregnancy.

Transcriptional profiling of human skin-resident Langerhans cells and CD1a+ dermal dendritic cells: differential activation states suggest distinct functions

In human skin, two main populations of dendritic cells (DC) can be discriminated: dermal DC (DDC) and epidermal Langerhans cells (LC). Although extensively studied, most of the knowledge about DDC and LC phenotype and function is obtained from studying DDC and LC cultured in vitro or DDC and LC migrated from skin explants. These studies have left the exact relationship between steady-state human LC and DDC unclear: in particular, whether CD1a+ DDC represent migrated LC or whether they constitute a separate subset. To gain further insight in the kinship between skin-resident CD1a+ DDC and LC, we analyzed CD1a+ DDC and LC, isolated from steady-state skin samples, by high-density microarray analysis. Results show that the CD1a+ DDC specifically express markers associated with DDC phenotype, such as the macrophage mannose receptor, DC-specific ICAM-grabbing nonintegrin, the scavenger receptor CD36, coagulation factor XIIIa, and chemokine receptor CCR5, whereas LC specifically express Langerin, membrane ATPase (CD39), and CCR6, all hallmarks of the LC lineage. In addition, under steady-state conditions, both DC subsets display a strikingly different activation status, indicative of distinct functional properties. CD1a+ DDC exhibit a more activated, proinflammatory, migratory, and T cell-stimulatory profile, as compared with LC, whereas LC mainly express molecules involved in cell adhesion and DC retention in the epidermis. In conclusion, transcriptional profiling is consistent with the notion that CD1a+ DDC and LC represent two distinct DC subsets but also that under steady-state conditions, CD1a+ DDC and epidermal LC represent opposites of the DC activation spectrum.

Human invariant Vα24+ natural killer T cells acquire regulatory functions by interacting with IL-10–treated dendritic cells

AbstractGlycolipid-reactive Vα24+ invariant natural killer T (iNKT) cells have been implicated in regulating a variety of immune responses and in the induction of immunologic tolerance. Activation of iNKT cells requires interaction with professional antigen-presenting cells, such as dendritic cells (DCs). We have investigated the capacity of distinct DC subsets to modulate iNKT cell functions. We demonstrate that tolerogenic DCs (tolDCs), generated by treatment of monocyte-derived DC with interleukin (IL)-10, induced regulatory functions in human iNKT cells. tolDCs, compared with immunogenic DCs, had reduced capacity to induce iNKT-cell proliferation, but these cells produced large amounts of IL-10 and acquired an anergic phenotype. These anergic Vα24+ iNKT cells were able to potently inhibit allogeneic CD4+ T-cell proliferation in vitro. Furthermore, the anergic Vα24+ iNKT cells could suppress DC maturation in vitro. We conclude that the interaction of iNKT cells with tolDCs plays an important role in the immune regulatory network, which might be exploited for therapeutic purposes.

307 Distinct Regulatory Dendritic Cell Subsets in Control of Treg Function in Acute Inflammation and Recovery from Colitis

307 Distinct Regulatory Dendritic Cell Subsets in Control of Treg Function in Acute Inflammation and Recovery from Colitis

Migration of Dendritic Cell Subsets and their Precursors

The ability of dendritic cells (DCs) to initiate and orchestrate immune responses is a consequence of their localization within tissues and their specialized capacity for mobilization. The migration of a given DC subset is typified by a restricted capacity for recirculation, contrasting markedly with T cells. Routes of DC migration into lymph nodes differ notably for distinct DC subsets. Here, we compare the distinct migratory patterns of plasmacytoid DCs (pDCs), CD8alpha(+) DCs, Langerhans cells, and conventional myeloid DCs and discuss how the highly regulated patterns of DC migration in vivo may affect their roles in immunity. Finally, to gain a more molecular appreciation of the specialized migratory properties of DCs, we review the signaling cascades that govern the process of DC migration.

The Signal Transducer STAT5 Inhibits Plasmacytoid Dendritic Cell Development by Suppressing Transcription Factor IRF8

The development of distinct dendritic cell (DC) subsets is regulated by cytokines. The ligand for the FMS-like tyrosine kinase 3 receptor (Flt3L) is necessary for plasmacytoid DC (pDC) and conventional DC (cDC) maturation. The cytokine GM-CSF inhibits Flt3L-driven pDC production while promoting cDC growth. We show that GM-CSF selectively utilized its signal transducer STAT5 to block Flt3L-dependent pDC development from the lineage-negative, Flt3+ (lin- Flt3+) bone-marrow subset. The signaling molecule STAT3, by contrast, was necessary for expansion of DC progenitors but not pDC maturation. In vivo, STAT5 suppressed pDC formation during repopulation of the DC compartment after bone-marrow ablation. GM-CSF-dependent STAT5 signaling rapidly extinguished pDC-related gene expression in lin- Flt3+ progenitors. Inspection of the Irf8 promoter revealed that STAT5 was recruited during GM-CSF-mediated suppression, indicating that STAT5 directly inhibited transcription of this critical pDC gene. Our results therefore show that GM-CSF controls the production of pDCs by employing STAT5 to suppress IRF8 and the pDC transcriptional network in lin- Flt3+ progenitors.

Significant Virus Replication in Langerhans Cells following Application of HIV to Abraded Skin: Relevance to Occupational Transmission of HIV

The cellular events that occur following occupational percutaneous exposure to HIV have not been defined. In this study, we studied relevant host cellular and molecular targets used for acquisition of HIV infection using split-thickness human skin explants. Blockade of CD4 or CCR5 before R5 HIV application to the epithelial surface of skin explants completely blocked subsequent HIV transmission from skin emigrants to allogeneic T cells, whereas preincubation with C-type lectin receptor inhibitors did not. Immunomagnetic bead depletion studies demonstrated that epithelial Langerhans cells (LC) accounted for >95% of HIV dissemination. When skin explants were exposed to HIV variants engineered to express GFP during productive infection, GFP+ T cells were found adjacent to GFP+ LC. In three distinct dendritic cell (DC) subsets identified among skin emigrants (CD1a+langerin+DC-specific intercellular adhesion molecule grabbing non-integrin (SIGN)- LC, CD1a+langerin-DC-SIGN- dermal DC, and CD1a-langerin-DC-SIGN+ dermal macrophages), HIV infection was detected only in LC. These results suggest that productive HIV infection of LC plays a critical role in virus dissemination from epithelium to cells located within subepithelial tissue. Thus, initiation of antiretroviral drugs soon after percutaneous HIV exposure may not prevent infection of LC, which is likely to occur rapidly, but may prevent or limit subsequent LC-mediated infection of T cells.

Expression of langerin/CD207 reveals dendritic cell heterogeneity between inbred mouse strains.

Langerin/CD207 is expressed by a subset of dendritic cells (DC), the epithelial Langerhans cells. However, langerin is also detected among lymphoid tissue DC. Here, we describe striking differences in langerin-expressing cells between inbred mouse strains. While langerin+ cells are observed in comparable numbers and with comparable phenotypes in the epidermis, two distinct DC subsets bear langerin in peripheral, skin-draining lymph nodes of BALB/c mice (CD11c(high) CD8alpha(high) and CD11c(low) CD8alpha(low)), whereas only the latter subset is present in C57BL/6 mice. The CD11c(high) subset is detected in mesenteric lymph nodes and spleen of BALB/c mice, but is virtually absent from C57BL/6 mice. Similar differences are observed in other mouse strains. CD11c(low) langerin+ cells represent skin-derived Langerhans cells, as demonstrated by their high expression of DEC-205/CD205, maturation markers, and recruitment to skin-draining lymph nodes upon imiquimod-induced inflammation. It will be of interest to determine the role of lymphoid tissue-resident compared to skin-derived langerin+ DC.