Distinct Dendritic Cell Populations Research Articles

The Potential of Dendritic Cell Subsets in the Development of Personalized Immunotherapy for Cancer Treatment.

Since the discovery of dendritic cells (DCs) in 1973 by Ralph Steinman, a tremendous amount of knowledge regarding these innate immunity cells has been accumulating. Their role in regulating both innate and adaptive immune processes is gradually being uncovered. DCs are proficient antigen-presenting cells capable of activating naive T-lymphocytes to initiate and generate effective anti-tumor responses. Although DC-based immunotherapy has not yielded significant results, the substantial number of ongoing clinical trials underscores the relevance of DC vaccines, particularly as adjunctive therapy or in combination with other treatment options. This review presents an overview of current knowledge regarding human DCs, their classification, and the functions of distinct DC populations. The stepwise process of developing therapeutic DC vaccines to treat oncological diseases is discussed, along with speculation on the potential of combined therapy approaches and the role of DC vaccines in modern immunotherapy.

Polyelectrolyte Coating of Ferumoxytol Differentially Impacts the Labeling of Inflammatory and Steady-State Dendritic Cell Subtypes.

Engineered magnetic nanoparticles (MNPs) are emerging as advanced tools for medical applications. The coating of MNPs using polyelectrolytes (PEs) is a versatile means to tailor MNP properties and is used to optimize MNP functionality. Dendritic cells (DCs) are critical regulators of adaptive immune responses. Functionally distinct DC subsets exist, either under steady-state or inflammatory conditions, which are explored for the specific treatment of various diseases, such as cancer, autoimmunity, and transplant rejection. Here, the impact of the PE coating of ferumoxytol for uptake into both inflammatory and steady-state DCs and the cellular responses to MNP labeling is addressed. Labeling efficiency by uncoated and PE-coated ferumoxytol is highly variable in different DC subsets, and PE coating significantly improves the labeling of steady-state DCs. Uncoated ferumoxytol results in increased cytotoxicity of steady-state DCs after labeling, which is abolished by the PE coating, while no increased cell death is observed in inflammatory DCs. Furthermore, uncoated and PE-coated ferumoxytol appear immunologically inert in inflammatory DCs, but they induce activation of steady-state DCs. These results show that the PE coating of MNPs can be applied to endow particles with desired properties for enhanced uptake and cell type-specific responses in distinct target DC populations.

A model of preferential pairing between epithelial and dendritic cells in thymic antigen transfer

Medullary thymic epithelial cells (mTECs), which produce and present self-antigens, are essential for the establishment of central tolerance. Since mTEC numbers are limited, their function is complemented by thymic dendritic cells (DCs), which transfer mTEC-produced self-antigens via cooperative antigen transfer (CAT). While CAT is required for effective T cell selection, many aspects remain enigmatic. Given the recently described heterogeneity of mTECs and DCs, it is unclear whether the antigen acquisition from a particular TEC subset is mediated by preferential pairing with a specific subset of DCs. Using several relevant Cre-based mouse models that control for the expression of fluorescent proteins, we have found that, in regards to CAT, each subset of thymic DCs preferentially targets a distinct mTEC subset(s). Importantly, XCR1+-activated DC subset represented the most potent subset in CAT. Interestingly, thymic DCs can also acquire antigens from more than one mTEC, and of these, monocyte-derived dendritic cells (moDCs) were determined to be the most efficient. moDCs also represented the most potent DC subset in the acquisition of antigen from other DCs. These findings suggest a preferential pairing model for the distribution of mTEC-derived antigens among distinct populations of thymic DCs.

Nucleic acid delivery of immune-focused SARS-CoV-2 nanoparticles drives rapid and potent immunogenicity capable of single-dose protection.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines may target epitopes that reduce durability or increase the potential for escape from vaccine-induced immunity. Using synthetic vaccinology, we have developed rationally immune-focused SARS-CoV-2 Spike-based vaccines. Glycans can be employed to alter antibody responses to infection and vaccines. Utilizing computational modeling and in vitro screening, we have incorporated glycans into the receptor-binding domain (RBD) and assessed antigenic profiles. We demonstrate that glycan-coated RBD immunogens elicit stronger neutralizing antibodies and have engineered seven multivalent configurations. Advanced DNA delivery of engineered nanoparticle vaccines rapidly elicits potent neutralizing antibodies in guinea pigs, hamsters, and multiple mouse models, including human ACE2 and human antibody repertoire transgenics. RBD nanoparticles induce high levels of cross-neutralizing antibodies against variants of concern with durable titers beyond 6 months. Single, low-dose immunization protects against a lethal SARS-CoV-2 challenge. Single-dose coronavirus vaccines via DNA-launched nanoparticles provide a platform for rapid clinical translation of potent and durable coronavirus vaccines.

Tissue-Specific Factors Differentially Regulate the Expression of Antigen-Processing Enzymes During Dendritic Cell Ontogeny.

Dendritic cells (DCs) form a collection of antigen-presenting cells (APCs) that are distributed throughout the body. Conventional DCs (cDCs), which include the cDC1 and cDC2 subsets, and plasmacytoid DCs (pDCs) constitute the two major ontogenically distinct DC populations. The pDCs complete their differentiation in the bone marrow (BM), whereas the cDC subsets derive from pre-committed BM precursors, the pre-cDC, that seed lymphoid and non-lymphoid tissues where they further differentiate into mature cDC1 and cDC2. Within different tissues, cDCs express distinct phenotype and function. Notably, cDCs in the thymus are exquisitely efficient at processing and presenting antigens in the class II pathway, whereas in the spleen they do so only upon maturation induced by danger signals. To appraise this functional heterogeneity, we examined the regulation of the expression of distinct antigen-processing enzymes during DC ontogeny. We analyzed the expression of cathepsin S (CTSS), cathepsin L (CTSL), and thymus-specific serine protease (TSSP), three major antigen-processing enzymes regulating class II presentation in cDC, by DC BM precursors and immature and mature cDCs from the spleen and thymus. We found that pre-cDCs in the BM express relatively high levels of these different proteases. Then, their expression is modulated in a tissue-specific and subset-specific manner with immature and mature thymic cDCs expressing overall higher levels than immature splenic cDCs. On the other hand, the TSSP expression level is selectively down-regulated in spleen pDCs, whereas CTSS and CTSL are both increased in thymic and splenic pDCs. Hence, tissue-specific factors program the expression levels of these different proteases during DC differentiation, thus conferring tissue-specific function to the different DC subsets.

Compartmentalization of dendritic cell and T-cell interactions in the lymph node: Anatomy of T-cell fate decisions.

Upon receiving cognate and co-stimulatory priming signals from antigen (Ag)-presenting dendritic cells (DCs) in secondary lymphoid tissues, naïve CD4+ T cells differentiate into distinct effector and memory populations. These alternate cell fate decisions, which ultimately control the T-cell functional attributes, are dictated by programming signals provided by Ag-bearing DCs and by other cells that are present in the microenvironment in which T-cell priming occurs. We know that DCs can be subdivided into multiple populations and that the various DC subsets exhibit differential capacities to initiate development of the different CD4+ T-helper populations. What is less well understood is why different subanatomic regions of secondary lymphoid tissues are colonized by distinct populations of Ag-presenting DCs and how the location of these DCs influences the type of T-cell response that will be generated. Here we review how chemokine receptors and their ligands, which position allergen and nematode-activated DCs within different microdomains of secondary lymphoid tissues, contribute to the establishment of IL-4 committed follicular helper T and type 2 helper cell responses.

Dendritic Cell Trafficking and Function in Rare Lung Diseases.

Dendritic cells (DCs) are highly specialized immune cells that capture antigens and then migrate to lymphoid tissue and present antigen to T cells. This critical function of DCs is well defined, and recent studies further demonstrate that DCs are also key regulators of several innate immune responses. Studies focused on the roles of DCs in the pathogenesis of common lung diseases, such as asthma, infection, and cancer, have traditionally driven our mechanistic understanding of pulmonary DC biology. The emerging development of novel DC reagents, techniques, and genetically modified animal models has provided abundant data revealing distinct populations of DCs in the lung, and allow us to examine mechanisms of DC development, migration, and function in pulmonary disease with unprecedented detail. This enhanced understanding of DCs permits the examination of the potential role of DCs in diseases with known or suspected immunological underpinnings. Recent advances in the study of rare lung diseases, including pulmonary Langerhans cell histiocytosis, sarcoidosis, hypersensitivity pneumonitis, and pulmonary fibrosis, reveal expanding potential pathogenic roles for DCs. Here, we provide a review of DC development, trafficking, and effector functions in the lung, and discuss how alterations in these DC pathways contribute to the pathogenesis of rare lung diseases.

The tumour microenvironment harbours ontogenically distinct dendritic cell populations with opposing effects on tumour immunity.

Various steady state and inflamed tissues have been shown to contain a heterogeneous DC population consisting of developmentally distinct subsets, including cDC1s, cDC2s and monocyte-derived DCs, displaying differential functional specializations. The identification of functionally distinct tumour-associated DC (TADC) subpopulations could prove essential for the understanding of basic TADC biology and for envisaging targeted immunotherapies. We demonstrate that multiple mouse tumours as well as human tumours harbour ontogenically discrete TADC subsets. Monocyte-derived TADCs are prominent in tumour antigen uptake, but lack strong T-cell stimulatory capacity due to NO-mediated immunosuppression. Pre-cDC-derived TADCs have lymph node migratory potential, whereby cDC1s efficiently activate CD8+ T cells and cDC2s induce Th17 cells. Mice vaccinated with cDC2s displayed a reduced tumour growth accompanied by a reprogramming of pro-tumoural TAMs and a reduction of MDSCs, while cDC1 vaccination strongly induces anti-tumour CTLs. Our data might prove important for therapeutic interventions targeted at specific TADC subsets or their precursors.

The Phenotypic Characterization of the Human Renal Mononuclear Phagocytes Reveal a Co-Ordinated Response to Injury.

Mammalian tissues contain networks of mononuclear phagocytes (MPh) that sense injury and orchestrate the response to it. In mice, this is affected by distinct populations of dendritic cells (DC), monocytes and macrophages and recent studies suggest the same is true for human skin and intestine but little is known about the kidney. Here we describe the analysis of MPh populations in five human kidneys and show they are highly heterogeneous and contain discrete populations of DC, monocytes and macrophages. These include: plasmacytoid DC (CD303+) and both types of conventional DC—cDC1 (CD141+ cells) and CD2 (CD1c+ cells); classical, non-classical and intermediate monocytes; and macrophages including a novel population of CD141+ macrophages clearly distinguishable from cDC1 cells. The relative size of the MPh populations differed between kidneys: the pDC population was bi-modally distributed being less than 2% of DC in two kidneys without severe injury and over 35% in the remaining three with low grade injury in the absence of morphological evidence of inflammation. There were profound differences in the other MPh populations in kidneys with high and low numbers of pDC. Thus, cDC1 cells were abundant (55 and 52.3%) when pDC were sparse and sparse (12.8–12.5%) when pDC were abundant, whereas the proportions of cDC2 cells and classical monocytes increased slightly in pDC high kidneys. We conclude that MPh are highly heterogeneous in human kidneys and that pDC infiltration indicative of low-grade injury does not occur in isolation but is part of a co-ordinated response affecting all renal DC, monocyte and macrophage populations.

Imaging of the cross-presenting dendritic cell subsets in the skin-draining lymph node

Dendritic cells (DCs) are antigen-presenting cells specialized for activating T cells to elicit effector T-cell functions. Cross-presenting DCs are a DC subset capable of presenting antigens to CD8(+) T cells and play critical roles in cytotoxic T-cell-mediated immune responses to microorganisms and cancer. Although their importance is known, the spatiotemporal dynamics of cross-presenting DCs in vivo are incompletely understood. Here, we study the T-cell zone in skin-draining lymph nodes (SDLNs) and find it is compartmentalized into regions for CD8(+) T-cell activation by cross-presenting DCs that express the chemokine (C motif) receptor 1 gene, Xcr1 and for CD4(+) T-cell activation by CD11b(+) DCs. Xcr1-expressing DCs in the SDLNs are composed of two different populations: migratory (CD103(hi)) DCs, which immigrate from the skin, and resident (CD8α(hi)) DCs, which develop in the nodes. To characterize the dynamic interactions of these distinct DC populations with CD8(+) T cells during their activation in vivo, we developed a photoconvertible reporter mouse strain, which permits us to distinctively visualize the migratory and resident subsets of Xcr1-expressing DCs. After leaving the skin, migratory DCs infiltrated to the deep T-cell zone of the SDLNs over 3 d, which corresponded to their half-life in the SDLNs. Intravital two-photon imaging showed that after soluble antigen immunization, the newly arriving migratory DCs more efficiently form sustained conjugates with antigen-specific CD8(+) T cells than other Xcr1-expressing DCs in the SDLNs. These results offer in vivo evidence for differential contributions of migratory and resident cross-presenting DCs to CD8(+) T-cell activation.

Functional Specialization of Skin Dendritic Cell Subsets in Regulating T Cell Responses.

Dendritic cells (DC) are a heterogeneous family of professional antigen-presenting cells classically recognized as most potent inducers of adaptive immune responses. In this respect, Langerhans cells have long been considered to be prototypic immunogenic DC in the skin. More recently this view has considerably changed. The generation of in vivo cell ablation and lineage tracing models revealed the complexity of the skin DC network and, in particular, established the existence of a number of phenotypically distinct Langerin+ and negative DC populations in the dermis. Moreover, by now we appreciate that DC also exert important regulatory functions and are required for the maintenance of tolerance toward harmless foreign and self-antigens. This review summarizes our current understanding of the skin-resident DC system in the mouse and discusses emerging concepts on the functional specialization of the different skin DC subsets in regulating T cell responses. Special consideration is given to antigen cross-presentation as well as immune reactions toward contact sensitizers, cutaneous pathogens, and tumors. These studies form the basis for the manipulation of the human counterparts of the murine DC subsets to promote immunity or tolerance for the treatment of human disease.

Targeting the Non-structural Protein 1 from Dengue Virus to a Dendritic Cell Population Confers Protective Immunity to Lethal Virus Challenge

Dengue is the most prevalent arboviral infection, affecting millions of people every year. Attempts to control such infection are being made, and the development of a vaccine is a World Health Organization priority. Among the proteins being tested as vaccine candidates in preclinical settings is the non-structural protein 1 (NS1). In the present study, we tested the immune responses generated by targeting the NS1 protein to two different dendritic cell populations. Dendritic cells (DCs) are important antigen presenting cells, and targeting proteins to maturing DCs has proved to be an efficient means of immunization. Antigen targeting is accomplished by the use of a monoclonal antibody (mAb) directed against a DC cell surface receptor fused to the protein of interest. We used two mAbs (αDEC205 and αDCIR2) to target two distinct DC populations, expressing either DEC205 or DCIR2 endocytic receptors, respectively, in mice. The fusion mAbs were successfully produced, bound to their respective receptors, and were used to immunize BALB/c mice in the presence of polyriboinosinic: polyribocytidylic acid (poly (I:C)), as a DC maturation stimulus. We observed induction of strong anti-NS1 antibody responses and similar antigen binding affinity irrespectively of the DC population targeted. Nevertheless, the IgG1/IgG2a ratios were different between mouse groups immunized with αDEC-NS1 and αDCIR2-NS1 mAbs. When we tested the induction of cellular immune responses, the number of IFN-γ producing cells was higher in αDEC-NS1 immunized animals. In addition, mice immunized with the αDEC-NS1 mAb were significantly protected from a lethal intracranial challenge with the DENV2 NGC strain when compared to mice immunized with αDCIR2-NS1 mAb. Protection was partially mediated by CD4+ and CD8+ T cells as depletion of these populations reduced both survival and morbidity signs. We conclude that targeting the NS1 protein to the DEC205+ DC population with poly (I:C) opens perspectives for dengue vaccine development.

Dendritic Cell Populations With Different Concentrations of Lipid Regulate Tolerance and Immunity in Mouse and Human Liver

Immune cells of the liver must be able to recognize and react to pathogens yet remain tolerant to food molecules and other nonpathogens. Dendritic cells (DCs) are believed to contribute to hepatic tolerance. Lipids have been implicated in dysfunction of DCs in cancer. Therefore, we investigated whether high lipid content in liver DCs affects induction of tolerance. Mouse and human hepatic nonparenchymal cells were isolated by mechanical and enzymatic digestion. DCs were purified by fluorescence-activated cell sorting or with immunomagnetic beads. DC lipid content was assessed by flow cytometry, immune fluorescence, and electron microscopy and by measuring intracellular component lipids. DC activation was determined from surface phenotype and cytokine profile. DC function was assessed in T-cell, natural killer (NK) cell, and NKT cell coculture assays as well as in vivo. We observed 2 distinct populations of hepatic DCs in mice and humans based on their lipid content and expression of markers associated with adipogenesis and lipid metabolism. This lipid-based dichotomy in DCs was unique to the liver and specific to DCs compared with other hepatic immune cells. However, rather than mediate tolerance, the liver DC population with high concentrations of lipid was immunogenic in multiple models; they activated T cells, NK cells, and NKT cells. Conversely, liver DCs with low levels of lipid induced regulatory T cells, anergy to cancer, and oral tolerance. The immunogenicity of lipid-rich liver DCs required their secretion of tumor necrosis factor α and was directly related to their high lipid content; blocking DC synthesis of fatty acids or inhibiting adipogenesis (by reducing endoplasmic reticular stress) reduced DC immunogenicity. Human and mouse hepatic DCs are composed of distinct populations that contain different concentrations of lipid, which regulates immunogenic versus tolerogenic responses in the liver.

The characteristics and immunoregulatory functions of regulatory dendritic cells induced by mesenchymal stem cells derived from bone marrow of patient with chronic myeloid leukaemia

Dendritic cells (DCs) are specialised antigen-presenting cells that play crucial roles in the initiation and regulation of immune responses. Recently, mesenchymal stem cells (MSCs) have gained further interest after demonstration of immunomodulatory effects on complicated interactions between T cells and even DCs. However, the mechanisms underlying these immunoregulatory effects of MSCs induced DCs are poorly understood. In addition, it is unclear whether the immunoregulatory functions of MSCs are altered in disease states. In this study, we showed that chronic myeloid leukaemia (CML) patients bone marrow derived MSCs (CML–MSC) could differentiate mature DCs (mDCs) into a distinct regulatory DC population, they had lower expression of CD40, CD80, CD83 and CD86. Similar to immature DCs (imDCs), CML–MSC induced DCs (CML–MSC–DCs) displayed powerful phagocytic capacity. Moreover, CML–MSC–DCs had the capacity to induce T cell anergy, another capacity of regulatory DCs. CML–MSC–DCs could inhibit the proliferation of T cells not only through TGF-β1, but also by inducing the production of Treg cells or T-cell anergy. At last, CML–MSC–DCs could efficiently induce more CD4+CD25+Foxp3+Tregs from naive CD4+CD25−Foxp3−T cells than that of normal-MSC–DCs in vitro. CML–MSC–DCs derived TGF-β1 was largely responsible for the increase in CD4+CD25+Foxp3+Tregs based on knockdown studies. The immunoregulatory effects of DCs induced by CML–MSCs enhance the potential use of autologous MSCs in cell therapy.

Immunomodulatory Function of Regulatory Dendritic Cells Induced by Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) provide an excellent model for development of stem cell therapeutics, and their potential treatment in the immunopathogenic diseases have gained further interest after demonstration of immunomodulatory effects on complicated interactions between T cells and even dendritic cells (DCs). However, the mechanisms underlying these immunoregulatory effects of MSCs are poorly understood. In this study, we show that bone marrow derived MSCs can differentiate mature DCs (mDCs) into a distinct regulatory DC population. Compared with mDCs, they have lower expression of CD1a, CD80, CD86 and CD40, but higher expression of CD11b. MSCs induced DCs (MSC-DCs) can hardly stimulate T-cell proliferation even when MSC-DCs are stimulated by LPS. In addition, high endocytosic capacity, low immunogenicity, and strong immunoregulatory function of MSC-DCs are also observed. Moreover, MSC-DCs can efficiently generate CD4+CD25+Foxp3+ Treg cells from CD4+CD25-Foxp3-T cells. The inhibitory function of MSC-DCs is mediated not only through TGF-β1, but also by inducing the production of Treg cells or T-cell anergy. These results demonstrate that the immunomodulatory effects of regulatory DCs induced by MSCs provide efficacious treatment for immunopathogenic diseases.

The Signaling Adaptor Eps8 Is an Essential Actin Capping Protein for Dendritic Cell Migration

Dendritic cells (DCs) flexibly adapt to different microenvironments by using diverse migration strategies that are ultimately dependent on the dynamics and structural organization of the actin cytoskeleton. Here, we have shown that DCs require the actin capping activity of the signaling adaptor Eps8 to polarize and to form elongated migratory protrusions. DCs from Eps8-deficient mice are impaired in directional and chemotactic migration in 3D invitro and are delayed in reaching the draining lymph node (DLN) invivo after inflammatory challenge. Hence, Eps8-deficient mice are unable to mount a contact hypersensitivity response. We have also shown that the DC migratory defect is cell autonomous and that Eps8 is required for the proper architectural organization of the actin meshwork and dynamics of cell protrusions. Yet, Eps8 is not necessary for antigen uptake, processing, and presentation. Thus, we have identified Eps8 as a unique actin capping protein specifically required for DC migration.

Differential gene expression analysis identifies murine Cacnb3 as strongly upregulated in distinct dendritic cell populations upon stimulation

Langerhans cells (LCs) represent the dendritic cell (DC) population in the epidermis. Among the set of genes induced in primary mouse LCs in response to stimulation, both isoforms of the voltage-dependent Ca 2+ channel (VDCC) regulatory subunit Cacnb3 as well as the DC maturation marker Fscn1 were upregulated most strongly. Comparable results were obtained for a recently described myeloid DC line (SP37A3). Other antigen presenting cell populations, namely, bone marrow-derived DCs, macrophages and primary B cells, showed no stimulation-associated upregulation of Cacnb3 expression. Pharmacological inhibition of Ca 2+ channel activity during the stimulation of SP37A3 cells enhanced their T cell stimulatory capacity, while selective inhibition of L-type VDCC had no effect. Both Cacnb3 isoforms, similar to Fscn1, required JNK and p38 kinase activity for stimulation-associated upregulation, and this process was inhibited by ERK and PI(3)K. The putative promoter region of Cacnb3 isoform 2, which we found to be less ubiquitously expressed than Cacnb3 isoform 1, exerted reporter activity in LC-like cell lines. Our findings suggest that Cacnb3 exerts its function in distinct activated DC populations. Further analysis of the regulatory region(s) facilitating stimulation-induced upregulation of Cacnb3 expression in these DC subsets will help to gain better insight into DC subset specific gene regulation.

Abundant and Superficial Expression of C-Type Lectin Receptors in Ectocervix of Women at Risk of HIV Infection

Dendritic cells (DCs) are among the first cells to encounter HIV after mucosal exposure and can bind virus via C-type lectin receptors (CLRs). Here, we characterized the distribution of various DC subtypes and the density of the CLRs, DC-SIGN, langerin, and mannose receptor in the ectocervix of HIV-seronegative women with low- and high-risk behavior for acquiring HIV. Cryosections from ectocervical biopsies, collected from sexually active low-risk healthy HIV immunoglobulin G-negative women (n = 10) and HIV immunoglobulin G-negative commercial sex workers (n = 8), were assessed by computerized image analysis. We identified various distinct DC populations. CD11c(-)CD1a(+)langerin(+) cells were localized in the epithelium, whereas CD11c(+)CD1a(-)DC-SIGN and CD11c(-)CD1a(-)CD68(+)DC-SIGN(+)mannose receptor(+) cells were restricted to the lamina propria of the ectocervix. CD123(+) cells were found at low incidence and did not express any of the investigated CLRs. The density of CLR expression was significantly higher in the high-risk as compared with the low-risk women. The superficial and abundant presence of potential HIV target cells makes the ectocervix a likely site for HIV transmission. The detected variations in density and localization of potential HIV receptors should be considered when developing topical prophylactic measures.

Nanoparticles target distinct dendritic cell populations according to their size

The efficiency of a vaccine largely depends on the appropriate targeting of the innate immune system, mainly through prolonged delivery of antigens and immunomodulatory substances to professional antigen-presenting cells in the lymphoid environment. Particulate antigens, such as virus-like particles (VLP) induce potent immune responses. However, little is known about the relative importance of direct drainage of free antigen to lymph nodes (LN) versus cellular transport and the impact of particle size on the process. Here, we show that nanoparticles traffic to the draining LN in a size-dependent manner. Whereas large particles (500-2000 nm) were mostly associated with dendritic cells (DC) from the injection site, small (20-200 nm) nanoparticles and VLP (30 nm) were also found in LN-resident DC and macrophages, suggesting free drainage of these particles to the LN. In vivo imaging studies in mice conditionally depleted of DC confirmed the capacity of small but not large particles to drain freely to the LN and demonstrated that DC are strictly required for transport of large particles from the injection site to the LN. These data provide evidence that particle size determines the mechanism of trafficking to the LN and show that only small nanoparticles can specifically target LN-resident cells.

Cover Picture: Nanoparticles target distinct dendritic cell populations according to their size – Eur. J. Immunol. 5/2008

AbstractThe cover shows a colour series of mouse footpads injected with small fluorescent nanoparticles. The image depicts the afferent lymphatic vessels connecting the injection site with the draining popliteal lymph node and the more distal sciatic lymph node. Lymphatic vessels (in green in the left row) run together with the veins (darker curves) and carry free draining antigen to the lymph nodes. This image was provided by the authors of Manolova (pp. 1404–1413), in which it is demonstrated that particle size critically influences the mode of antigen transport to the draining lymph nodes; DC are strictly required for transport of large (500–2000 nm) particles, whereas smaller particles (20–200 nm), such as virus‐like particles (30 nm), drain freely.