Three populations of cells with dendritic morphology exist in peripheral blood, only one of which is infectable with human immunodeficiency virus type 1

CD83 Regulates the Immune Responses in Inflammatory Disorders

Activating the immune system plays an important role in maintaining physiological homeostasis and defending the body against harmful infections. However, abnormalities in the immune response can lead to various immunopathological responses and severe inflammation. The activation of dendritic cells (DCs) can influence immunological responses by promoting the differentiation of T cells into various functional subtypes crucial for the eradication of pathogens. CD83 is a molecule known to be expressed on mature DCs, activated B cells, and T cells. Two isotypes of CD83, a membrane-bound form and a soluble form, are subjects of extensive scientific research. It has been suggested that CD83 is not only a ubiquitous co-stimulatory molecule but also a crucial player in monitoring and resolving inflammatory reactions. Although CD83 has been involved in immunological responses, its functions in autoimmune diseases and effects on pathogen immune evasion remain unclear. Herein, we outline current immunological findings and the proposed function of CD83 in inflammatory disorders.

Dendritic cells: microbial clearance via autophagy and potential immunobiological consequences for periodontal disease

Dendritic cells are potent antigen‐capture and antigen‐presenting cells that play a key role in the initiation and regulation of the adaptive immune response. This process of immune homeostasis, as maintained by dendritic cells, is susceptible to dysregulation by certain pathogens during chronic infections. Such dysregulation may lead to disease perpetuation with potentially severe systemic consequences. Here we discuss in detail how intracellular pathogens exploit dendritic cells and escape degradation by altering or evading autophagy. This novel mechanism explains, in part, the chronic, persistent nature observed in several immuno‐inflammatory diseases, including periodontal disease. We also propose a hypothetical model of the plausible role of autophagy in the context of periodontal disease. Promotion of autophagy may open new therapeutic strategies in the search of a ‘cure’ for periodontal disease in humans.

Distinct phenotype, longitudinal changes of numbers and cell-associated virus in blood dendritic cells in SIV-infected CD8-lymphocyte depleted macaques

Loss of circulating CD123+ plasmacytoid dendritic cells (pDCs) during HIV infection is well established. However, changes of myeloid DCs (mDCs) are ambiguous since they are studied as a homogeneous CD11c+ population despite phenotypic and functional heterogeneity. Heterogeneity of CD11c+ mDCs in primates is poorly described in HIV and SIV infection. Using multiparametric flow cytometry, we monitored longitudinally cell number and cell-associated virus of CD123+ pDCs and non-overlapping subsets of CD1c+ and CD16+ mDCs in SIV-infected CD8-depleted rhesus macaques. The numbers of all three DC subsets were significantly decreased by 8 days post-infection. Whereas CD123+ pDCs were persistently depleted, numbers of CD1c+ and CD16+ mDCs rebounded. Numbers of CD1c+ mDCs significantly increased by 3 weeks post-infection while numbers of CD16+ mDCs remained closer to pre-infection levels. We found similar changes in the numbers of all three DC subsets in CD8 depleted animals as we found in animals that were SIV infected animals that were not CD8 lymphocyte depleted. CD16+ mDCs and CD123+ pDCs but not CD1c+ mDCs were significantly decreased terminally with AIDS. All DC subsets harbored SIV RNA as early as 8 days and then throughout infection. However, SIV DNA was only detected in CD123+ pDCs and only at 40 days post-infection consistent with SIV RNA, at least in mDCs, being surface-bound. Altogether our data demonstrate that SIV infection differently affects CD1c+ and CD16+ mDCs where CD16+ but not CD1c+ mDCs are depleted and might be differentially regulated in terminal AIDS. Finally, our data underline the importance of studying CD1c+ and CD16+ mDCs as discrete populations, and not as total CD11c+ mDCs.

Gain of function in the immune system caused by a ryanodine receptor 1 mutation

Mutations in RYR1, the gene encoding ryanodine receptor 1, are linked to a variety of neuromuscular disorders including malignant hyperthermia (MH), a pharmacogenetic hypermetabolic disease caused by dysregulation of Ca(2+) in skeletal muscle. RYR1 encodes a Ca(2+) channel that is predominantly expressed in skeletal muscle sarcoplasmic reticulum, where it is involved in releasing the Ca(2+) necessary for muscle contraction. Other tissues, however, including cells of the immune system, have been shown to express ryanodine receptor 1; in dendritic cells its activation leads to increased surface expression of major histocompatibility complex II molecules and provides synergistic signals leading to cell maturation. In the present study, we investigated the impact of an MH mutation on the immune system by studying the RYR1Y522S knock-in mouse. Our results show that there are subtle but significant differences both in resting 'non-challenged' mice as well as in mice treated with antigenic stimuli, in particular the knock-in mice: (i) have dendritic cells that are more efficient at stimulating T cell proliferation, (ii) have higher levels of natural IgG1 and IgE antibodies, and (iii) are faster and more efficient at mounting a specific immune response in the early phases of immunization. We suggest that some gain-of-function MH-linked RYR1 mutations might offer selective immune advantages to their carriers. Furthermore, our results raise the intriguing possibility that pharmacological activation of RyR1 might be exploited for the development of new classes of vaccines and adjuvants.

Isolation and generation of human dendritic cells

Dendritic cells are highly specialized antigen-presenting cells (APC), which may be isolated or generated from human blood mononuclear cells. Although mature blood dendritic cells normally represent ∼0.2% of human blood mononuclear cells, their frequency can be greatly increased using the cell enrichment methods described in this unit. More highly purified dendritic cell preparations can be obtained from these populations by sorting of fluorescence-labeled cells. Alternatively, dendritic cells can be generated from monocytes by culture with the appropriate cytokines, as described here. In addition, a negative selection approach is provided that may be employed to generate cell preparations that have been depleted of dendritic cells to be used for comparison in functional studies.

Immunosuppressive Effect of Cordyceps CS-4 on Human Monocyte-Derived Dendritic Cellsin Vitro

Cordyceps CS-4 (C.CS-4), a vegetative form of Cordyceps that contains the same active compounds as the fruit body, is widely used as a substitute of Cordyceps in China. A number of studies have shown that Cordyceps can positively stimulate the activation of T lymphocytes, B lymphocytes, natural killer cells, and macrophages. In our previous study, we found that C.CS-4 could inhibit the proliferation of CD4+ T cells in autoimmune diseases and prevent the lymphocyte infiltration in tissues. However, it is still unclear how the lymphocytes are regulated by C.CS-4. In this study, we investigate the effect of C.CS-4 on human monocyte-derived dendritic cells ( Mo -DCs), which are generated from PBMCs by the treatment with GM-CSF and IL-4. It is observed that Mo -DCs pretreated with C.CS-4 show an immature phenotype. Moreover, C.CS-4 significantly inhibits proliferation of CD4+ T cells, attenuates the production of cytokines in Mo -DCs and balances the Th1 and Th2 response in immune system. Our findings indicate that C.CS-4 exerts the immunosuppressive effect through inhibiting the CD4+ T cells proliferation, regulating cytokine secretions of Th1 and Th2 response ( Mo -DCs) and inducing phenotypic immature of Mo -DCs which may be related to the antigen presenting dysfunction.

Isolation and generation of human dendritic cells

Dendritic cells are highly specialized antigen-presenting cells (APC), which may be isolated or generated from human blood mononuclear cells. Although mature blood dendritic cells normally represent 0.2% of human blood mononuclear cells, their frequency can be greatly increased using the cell enrichment methods described in this unit. More highly purified dendritic cell preparations can be obtained from these populations by sorting of fluorescence-labeled cells. Alternatively, dendritic cells can be generated from monocytes by culture with the appropriate cytokines, as described here. In addition, a negative selection approach is provided that may be employed to generate cell preparations that have been depleted of dendritic cells to be used for comparison in functional studies.

The CD83 reporter mouse elucidates the activity of the CD83 promoter in B, T, and dendritic cell populations in vivo

CD83 is the major surface marker identifying mature dendritic cells (DCs). In this study, we report the generation of reporter mice expressing EGFP under the control of the CD83 promoter. We have used these mice to characterize CD83 expression by various immune system cell types both in vivo and ex vivo and under steady-state conditions and in response to stimulation with a Toll-like receptor (TLR) ligand. With those mice we could prove in vivo that the CD83 promoter is highly active in all DCs and B cells in lymphoid organs. Interestingly, this promoter activity in B cells mainly depended on the stage of development, is up-regulated in the late pre-B cell stage, and was maintained on a high level in all peripheral B cells. We also confirmed that CD83 in those cells is mainly intracellular but is up-regulated after TLR stimulation. Otherwise, CD83 promoter activity in T cells seemed to depend on stimulation and could be found mainly in CD4(+)CD25(+) and CD8(+)CD25(+) T cells and in CD4(+) and CD8(+) memory cells. In addition, we identified the murine homologues of the human CD83 splice variants. In contrast to those in human, those extremely rare short transcripts were never found without the expression of the highly dominant full-length form. So, the murine CD83 surface expression is mainly regulated posttranslationally in vivo. Our CD83 reporter mice represent a useful mouse model for monitoring the activation status and migration of DCs and lymphocytes under various conditions, and our results provide much needed clarification of the true nature of CD83 promoter activity.

MCS-18, a novel natural product isolated from Helleborus purpurascens, inhibits dendritic cell activation and prevents autoimmunity as shown in vivo using the EAE model

Here we report for the first time that MCS-18, a novel natural product isolated from Helleborus purpurascens, is able to inhibit the expression of typical molecules of mature dendritic cells (DC) such as CD80, CD86, and especially of CD83 subsequently leading to a clear and dose-dependent inhibition of the DC-mediated T-cell stimulation. Furthermore, MCS-18 impeded the formation of the typical DC/T-cell clusters, which are essential to induce potent immune responses. Interestingly, MCS-18 also inhibited CCR7 expression on DC which subsequently lead to a dose-dependent block of the CCL19-mediated DC migration. MCS-18 not only inhibited the DC-mediated T-cell stimulation but also the anti-CD3/anti-CD28-mediated T-cell stimulation. Strikingly, MCS-18 also strongly reduced the paralysis associated with the experimental autoimmune encephalomyelitis (EAE), which is a murine model for human multiple sclerosis, in a prophylactic as well as in a "real" therapeutic setting. Even when the EAE was induced for a second time, the MCS-18-treated animals were still protected, suggesting that MCS-18 induces a long-lasting suppressive effect. In addition, and very important for the potential practical application in humans, MCS-18 was also active when administered orally. MCS-18 treatment almost completely reduced leukocyte infiltration in the brain and in the spinal cord. In conclusion, using in vitro as well in vivo assays we were able to show that MCS-18 exerts a strong immunosuppressive activity with remarkable potential for the therapy of diseases characterized by a pathologically over-activated immune system.

CD83 expression is a sensitive marker of activation required for B cell and CD4+ T cell longevity in vivo

CD83 is a surface marker that differentiates immature and mature human dendritic cell populations. Thymic epithelial cell expression of CD83 is also necessary for efficient CD4+ T cell development in mice. The altered phenotypes of peripheral B and CD4+ T cells, and the reduction of peripheral CD4+ T cells in CD83-/- mice, suggest additional functions for CD83. To assess this, a panel of mAbs was generated to characterize mouse CD83 expression by peripheral leukocytes. As in humans, activation of conventional and plasmacytoid murine dendritic cell subsets led to rapid up-regulation of CD83 surface expression in mice. In primary and secondary lymphoid compartments, a subset of B cells expressed low-level CD83, while CD83 was not detected on resting T cells. However, CD83 was prominently up-regulated on the majority of spleen B and T cells within hours of activation in vitro. In vivo, a low dose of hen egg lysozyme (1 microg) induced significant CD83 but not CD69 expression by Ag-specific B cells within 4 h of Ag challenge. Although B cell development appeared normal in CD83-/- mice, B and CD4+ T cell expression of CD83 was required for lymphocyte longevity in adoptive transfer experiments. Thus, the restricted expression pattern of CD83, its rapid induction following B cell and T cell activation, and its requirement for B cell and CD4+ T cell longevity demonstrate that CD83 is a functionally significant and sensitive marker of early lymphocyte activation in vivo.

CD83 influences cell-surface MHC class II expression on B cells and other antigen-presenting cells

CD83 is a member of the Ig superfamily expressed primarily by mature dendritic cells (DCs). In mice, CD83 expression by thymic stromal cells regulates CD4(+) T cell development, with CD83(-/-) mice demonstrating dramatic reductions in both thymus and peripheral CD4(+) T cells. In this study, CD83 expression was also found to affect MHC class II antigen expression within the thymus and periphery. CD83 deficiency reduced cell-surface class II antigen expression by 25-50% on splenic B cells and DCs, thymic epithelial cells and peritoneal macrophages. Reduced class II expression was a stable and intrinsic property that resulted from increased internalization of class II from the surface of CD83(-/-) B cells. Otherwise, class II antigen transcription, intracellular expression, heterodimer structure, antigen processing and antigen presentation were normal. Reduced class II antigen expression was not the primary cause of the CD83(-/-) phenotype since thymocyte and peripheral T cell development was normal in class II(+/-) mice. Comparable blocks in CD4(+) thymocyte development were also observed in CD83(-/-) and CD83(-/-)class II(+/-) littermates. TCR and CD69 expression patterns in CD83(-/-) mice further suggested that double-positive thymocytes proceed through the class II-dependent stages of positive selection in the absence of CD83. These studies further emphasize a role for CD83 in lymphocyte development and immune regulation and reveal an unexpected role for CD83 expression in influencing cell-surface MHC class II turnover.

CD83: an update on functions and prospects of the maturation marker of dendritic cells

CD83 is one of the most characteristic cell surface markers for fully matured dendritic cells (DCs). In their function as antigen presenting cells they induce T-cell mediated immune responses. In this review we provide an overview on well described and proposed functions of this molecule as well as on very recent insights and new hypothesis. Already the CD83 messenger RNA processing differs remarkably from the processing of other cellular mRNAs: instead of the usual TAP mRNA export pathway, the CD83 mRNA is exported by the specific CRM1-mediated pathway, utilized only by a minority of cellular mRNAs. On the protein level, two different isoforms of CD83 exist: a membrane-bound and a soluble form. The isoforms are generated by different subsets of cells, including DCs, T-cells and B-cells, and also differ in their biological function. While the membrane-bound CD83 is of immune stimulatory capacity, activates T-cells and is important for the generation of thymocytes, the soluble CD83 has the opposite effect and has an immune inhibitory capacity. Due to its immune inhibitory function, CD83 has great potential for treatment of autoimmune diseases, for organ transplantations, and for immunotherapy, just to name a few examples. Moreover, some viruses prevent recognition by the host's immune system by specifically targeting CD83 surface expression.

A limited course of soluble CD83 delays acute cellular rejection of MHC-mismatched mouse skin allografts

CD83 is a surface marker expressed on matured dendritic cells (DCs). It plays a pivotal role in the mediation of DC/T cell interaction and induction of T-cell activation. Previous studies have suggested that a soluble form of CD83 could suppress DC maturation and inhibit T-cell activation and, as a result, it can prevent paralysis associated with experimental autoimmune encephalomyelitis. Here, we explored its potential effect on allograft rejection in a fully major histocompatibility complex-mismatched murine skin transplantation model. A form of mouse soluble CD83 (CD83-Ig) fused the extracellular domain of murine CD83 with human IgG1alpha Fc tail was purified from transfected COS-7 cell. It was found that the treatment of recipient mice with CD83-Ig significantly delayed allograft rejection. Especially, when T cells originated from recipients treated with CD83-Ig re-stimulated with donor-specific splenocytes, they showed a significant reduced responding capability as compared with that of originated from control recipients. In line with these results, a reduction for serum IFN-gamma and IL-2 and a decreased mRNA expression of IFN-gamma and IL-2 in allograft infiltrated immune cells were also observed. Our results suggest that CD83-Ig could be useful for the treatment of allograft rejection in combination with other therapeutic strategies.

Leukocyte-specific protein 1 interacts with DC-SIGN and mediates transport of HIV to the proteasome in dendritic cells

Dendritic cells (DCs) capture and internalize human immunodeficiency virus (HIV)-1 through C-type lectins, including DC-SIGN. These cells mediate efficient infection of T cells by concentrating the delivery of virus through the infectious synapse, a process dependent on the cytoplasmic domain of DC-SIGN. Here, we identify a cellular protein that binds specifically to the cytoplasmic region of DC-SIGN and directs internalized virus to the proteasome. This cellular protein, leukocyte-specific protein 1 (LSP1), was defined biochemically by immunoprecipitation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. LSP1 is an F-actin binding protein involved in leukocyte motility and found on the cytoplasmic surface of the plasma membrane. LSP1 interacted specifically with DC-SIGN and other C-type lectins, but not the inactive mutant DC-SIGNΔ35, which lacks a cytoplasmic domain and shows altered virus transport in DCs. LSP1 diverts HIV-1 to the proteasome. Down-regulation of LSP1 with specific small interfering RNAs in human DCs enhanced HIV-1 transfer to T cells, and bone marrow DCs from lsp1^−/− mice also showed an increase in transfer of HIV-1_BaL to a human T cell line. Proteasome inhibitors increased retention of viral proteins in lsp1^+/+ DCs, and substantial colocalization of virus to the proteasome was observed in wild-type compared with LSP1-deficient cells. Collectively, these data suggest that LSP1 protein facilitates virus transport into the proteasome after its interaction with DC-SIGN through its interaction with cytoskeletal proteins.

Dendritic cell-mediated viral transmission: a potential drug target?

Dendritic cells (DCs) are important in the sexual transmission of HIV-1, the most common route of acquiring HIV-1. HIV-1 subverts the biological function of DCs to facilitate its transport from site of entry at mucosal tissues to lymphoid tissues to infect T cells. Recent data have furthered our understanding of how DCs mediate viral transmission to T cells. DCs capture HIV-1 through specific attachment receptors, such as DC-SIGN, which not only facilitate HIV-1 transmission, but also infection of DCs. Therefore, these receptors are very promising targets for the design of inhibitors or vaccination strategies to prevent mucosal HIV-1 transmission. It is becoming evident that other viruses also use DCs for their transmission. This review will discuss the mechanism of HIV-1 transmission and potential intervention strategies.

HIV interactions with dendritic cells: has our focus been too narrow?

Although few in number, dendritic cells (DCs) are heterogeneous, ubiquitous, and are crucial for protection against pathogens. In this review, the different DC subpopulations have been described and aspects of DC biology are discussed. DCs are important, not only in the pathogenesis of HIV, but also in the generation of anti-HIV immune responses. This review describes the roles that DC are thought to play in HIV pathogenesis, including uptake and transport of virus. We have also discussed the effects that the virus exerts on DCs such as infection and dysfunction. Then we proceed to focus on DC subsets in different organs and show how widespread the effects of HIV are on DC populations. It is clear that the small number of studies on tissue-derived DCs limits current research into the pathogenesis of HIV.

Dendritic cells from chronic lymphocytic leukemia patients are normal regardless of Ig V gene mutation status

Patients with B-type chronic lymphocytic leukemia (B-CLL) segregate into 2 subgroups based on the mutational status of the immunoglobulin (Ig) V genes and the patients in these subgroups follow very different clinical courses. To examine whether dendritic cells (DCs) generated from CLL patients can be candidates for immune therapy, we compared the phenotypic and functional capacities of DCs generated from patients of the 2 CLL subgroups (normal age-matched subjects [normal-DCs]). Our data show that immature DCs from B-CLL patients (B-CLL-DCs) have the same capacity to take up antigen as those from normal controls. Furthermore, B-CLL-DCs generated from the 2 CLL subgroups up-regulated MHC-II, CD80, CD86, CD83, CD40, and CD54 and down-regulated CD206 in response to stimulation with a cocktail of cytokines (CyC) and secreted increased levels of tumor necrosis factor alpha, interleukin (IL)-8, IL-6, IL-12 (p70), and RANTES in a manner typical of mature normal-DCs. Interestingly, CD54 was significantly more up-regulated by CyC in B-CLL-DCs compared with normal-DCs. Except for CD54, no significant differences in surface molecule expression were observed between normal-DCs and B-CLL-DCs. B-CLL-DCs from both subgroups, including 6 patients with VH1-69, that usually fare poorly, presented tetanus toxoid to autologous T cells in vitro similar to normal- DCs. Our data show that DCs generated from the B-CLL subgroup with unmutated Ig V genes are functionally normal. These results are very promising for the use of DCs from patients with poor prognosis for immunotherapy.

IL-18-induced CD83+CCR7+ NK helper cells

In addition to their cytotoxic activities, natural killer (NK) cells can have immunoregulatory functions. We describe a distinct "helper" differentiation pathway of human CD56+CD3- NK cells into CD56+/CD83+/CCR7+/CD25+ cells that display high migratory responsiveness to lymph node (LN)-associated chemokines, high ability to produce interferon-gamma upon exposure to dendritic cell (DC)- or T helper (Th) cell-related signals, and pronounced abilities to promote interleukin (IL)-12p70 production in DCs and the development of Th1 responses. This helper pathway of NK cell differentiation, which is not associated with any enhancement of cytolytic activity, is induced by IL-18, but not other NK cell-activating factors. It is blocked by prostaglandin (PG)E2, a factor that induces a similar CD83+/CCR7+/CD25+ LN-homing phenotype in maturing DCs. The current data demonstrate independent regulation of the "helper" versus "effector" pathways of NK cell differentiation and novel mechanisms of immunoregulation by IL-18 and PGE2.

Human BDCA-1-positive blood dendritic cells differentiate into phenotypically distinct immature and mature populations in the absence of exogenous maturational stimuli: differentiation failure in HIV infection

Current immunological opinion holds that myeloid dendritic cell (mDC) precursors migrate from the blood to the tissues, where they differentiate into immature dermal- and Langerhans-type dendritic cells (DC). Tissue DC require appropriate signals from pathogens or inflammatory cytokines to mature and migrate to secondary lymphoid tissue. We show that purified blood mDC cultured in vitro with GM-CSF and IL-4, but in the absence of added exogenous maturation stimuli, rapidly differentiate into two maturational and phenotypically distinct populations. The major population resembles immature dermal DC, being positive for CD11b, CD1a, and DC-specific ICAM-3-grabbing nonintegrin. They express moderate levels of MHC class II and low levels of costimulatory molecules. The second population is CD11b(-/low) and lacks CD1a and DC-specific ICAM-3-grabbing nonintegrin but expresses high levels of MHC class II and costimulatory molecules. Expression of CCR7 on the CD11b(-/low) population and absence on the CD11b(+) cells further supports the view that these cells are mature and immature, respectively. Differentiation into mature and immature populations was not blocked by polymyxin B, an inhibitor of LPS. Neither population labeled for Langerin, E-cadherin, or CCR6 molecules expressed by Langerhans cells. Stimulation of 48-h cultured DC with LPS, CD40L, or poly(I:C) caused little increase in MHC or costimulatory molecule expression in the CD11b(-/low) DC but caused up-regulated expression in the CD11b(+) cells. In HIV-infected individuals, there was a marked decrease in the viability of cultured blood mDC, a failure to differentiate into the two populations described for normal donors, and an impaired ability to stimulate T cell proliferation.

CD83 is a dimer: Comparative analysis of monomeric and dimeric isoforms

Recently, we reported that soluble CD83 has a strong immunosuppressive activity in vitro as well as in vivo. Sequence alignment of CD83 between different species revealed the presence of five cysteines in the extracellular Ig-domain of the protein. This opens up the possibility that four cysteines are involved in the formation of two intramolecular disulfide bonds and a possible involvement of the remaining fifth cysteine in the formation of an intermolecular covalent disulfide bond, leading to the dimerization of the extracellular protein domains. Using recombinant mutational analyses, where the fifth cytosine at amino acid position 129 was mutated to a serine, we could prove that the fifth cysteine residue was indeed necessary for the dimerization. Functional analyses revealed that the mutant protein inhibited almost completely the upregulation of CD83-expression during DC maturation. Furthermore, the functional activity of the mutant protein was investigated using MLR assays and we could show that the mutant soluble CD83 protein inhibited DC-mediated allogeneic T-cell stimulation in vitro.

Mechanisms promoting dendritic cell-mediated transmission of HIV

Dendritic cells (DC) survey epithelial or mucosal surfaces for antigens, take them up via their endocytic or phagocytic receptors, process the captured antigens and migrate to the lymphatic tissues. In the draining lymph nodes they present the immunogenic peptides to T cells thereby inducing antigen-specific immune responses. HIV-1 in turn seems to have developed mechanisms to exploit the natural trafficking of DC to establish infection in its primary targets, the CD4+ T cells. This review discusses several aspects of DC-HIV interactions with a main focus on the attachment, internalisation and transmission of the virus by DC to cells, susceptible for infection with HIV.

Long-term productive human immunodeficiency virus infection of CD1a-sorted myeloid dendritic cells

Myeloid, CD1a-sorted dendritic cells (MDC) productively replicated human immunodeficiency virus strains encoding envelope genes of either primary X4R5 or R5 strains for up to 45 days. Cell-free supernatant collected from long-term infected MDC, which had been exposed to an X4R5 virus 45 days earlier, was still infectious when placed over activated T cells. These data imply that DC can act as a persistent reservoir of infectious virus.

Infection of specific dendritic cells by CCR5-tropic human immunodeficiency virus type 1 promotes cell-mediated transmission of virus resistant to broadly neutralizing antibodies

The tropism of human immunodeficiency virus type 1 for chemokine receptors plays an important role in the transmission of AIDS. Although CXCR4-tropic virus is more cytopathic for T cells, CCR5-tropic strains are transmitted more frequently in humans for reasons that are not understood. Phenotypically immature myeloid dendritic cells (mDCs) are preferentially infected by CCR5-tropic virus, in contrast to mature mDCs, which are not susceptible to infection but instead internalize virus into a protected intracellular compartment and enhance the infection of T cells. Here, we define a mechanism to explain preferential transmission of CCR5-tropic viruses based on their interaction with mDCs and sensitivity to neutralizing antibodies. Infected immature mDCs differentiated normally and were found to enhance CCR5-tropic but not CXCR4-tropic virus infection of T cells even in the continuous presence of neutralizing antibodies. Infectious synapses also formed normally in the presence of such antibodies. Infection of immature mDCs by CCR5-tropic virus can therefore establish a pool of infected cells that can efficiently transfer virus at the same time that they protect virus from antibody neutralization. This property of DCs may enhance infection, contribute to immune evasion, and could provide a selective advantage for CCR5-tropic virus transmission.

HIV-1-infected monocyte-derived dendritic cells do not undergo maturation but can elicit IL-10 production and T cell regulation

Dendritic cells (DCs) undergo maturation during virus infection and thereby become potent stimulators of cell-mediated immunity. HIV-1 replicates in immature DCs, but we now find that infection is not accompanied by many components of maturation in either infected cells or uninfected bystanders. The infected cultures do not develop potent stimulating activity for the mixed leukocyte reaction (MLR), and the DCs producing HIV-1 gag p24 do not express CD83 and DC-lysosome-associated membrane protein maturation markers. If different maturation stimuli are applied to DCs infected with HIV-1, the infected cells selectively fail to mature. When DCs from HIV-1-infected patients are infected and cultured with autologous T cells, IL-10 was produced in 6 of 10 patients. These DC-T cell cocultures could suppress another immune response, the MLR. The regulation was partially IL-10-dependent and correlated in extent with the level of IL-10 produced. Suppressor cells only developed from infected patients, rather than healthy controls, and the DCs had to be exposed to live virus rather than HIV-1 gag peptides or protein. These results indicate that HIV-1-infected DCs have two previously unrecognized means to evade immune responses: maturation can be blocked reducing the efficacy of antigen presentation from infected cells, and T cell-dependent suppression can be induced.

Productive infection of dendritic cells by simian immunodeficiency virus in macaque intestinal tissues

Dendritic cells (DCs) are potent antigen-presenting cells that likely play multiple roles in human immunodeficiency virus-1 (HIV-1) and simian immunodeficiency virus (SIV) pathogenesis. This paper describes the effects of pathogenic SIV infection on the networks of DCs in rhesus macaque (Macaca mulatta) intestinal tissues. Intestinal tissues were obtained from macaques at different stages of disease following infection with the pathogenic SIV/DeltaB670 isolate. The patterns and levels of expression of SIV and DC-associated mRNAs were examined and quantitated directly in intestinal tissue sections. In situ hybridization was performed for SIV, DC-specific ICAM3-grabbing non-integrin (DC-SIGN), DC-specific lysosome-associated membrane glycoprotein (DC-LAMP), DC-specific C-type lectin 1 (DECTIN-1), CC chemokine receptor 6 (CCR6), CCR7, and macrophage inflammatory protein 3alpha (MIP-3alpha/CCL20) mRNAs and quantitative image analysis was performed to measure mRNA expression levels. To identify the cell types productively infected by SIV, simultaneous in situ hybridization and immunohistochemical staining were performed. The DC networks in macaque intestinal tissues were found to be extensive and although they generally remained intact during the course of SIV infection, there were alterations in the expression of markers for immature DCs. One alteration was an increase in the expression in intestinal submucosa of DC-SIGN, a molecule that binds to HIV-1/SIV and increases its infectivity. Concomitant with this increase, it was found that during AIDS, the population of productively infected cells included DCs, based on co-expression of DC-SIGN and DECTIN-1 mRNAs. These data indicate that SIV infection affects subpopulations of macaque intestinal DCs, including productive infection of DC-SIGN+ DCs, the consequences of which are likely to be ongoing viral propagation and decreased immunostimulatory function.

Peripheral blood Dendritic cells are not a major reservoir for HIV type 1 in infected individuals on virally suppressive HAART

Dendritic cells (DCs) are potent antigen-presenting cells, and their physiological localization in tissues that interact with the external environment is important as a first barrier against pathogens such as human immunodeficiency virus type I (HIV-1). Several models have been proposed to explain the possible role of DCs as a reservoir for HIV-1 in patients on virally suppressive highly active antiretroviral therapy (HAART). However, the low yield of cell isolates has made this evaluation a difficult task. The present study analyzes whether peripheral blood DCs from HIV-1-infected individuals on virally suppressive HAART, with plasma HIV-1 RNA levels of less than 50 copies/ml, carry either HIV-1 provirus and/or HIV-1 virions. Peripheral blood DCs were isolated from a cohort of 10 HIV-1-seropositive men taking suppressive HAART. In five patients, plasmacytoid and myeloid dendritic cells were isolated to attempt to identify their respective roles in HIV-1 residual disease. Viral out-growth assays were performed in vitro, as well as gag and R/U5 polymerase chain reaction (PCR) amplification of viral RNA and DNA, respectively, from DC and peripheral blood mononuclear cell (PBMC) extracts. Fluorescence activated cell-sorting (FACS) data revealed cellular yields from 85.90 to 95.18%, of relatively pure DCs isolated from patients' PBMCs. Although HIV-1 RNA gag and DNA RU/5 were detected in all PBMC samples isolated from the patients, proviral DNA and viral RNA forms were not detected in any of the DC isolates. In addition, no replication-competent virus was demonstrated in DC coculture assays, while virus was isolated from each patients' CD8+ T-lymphocyte-depleted PBMC cocultures. Furthermore, HIV-1 gag proviral DNA was not detected in either plasmacytoid or myeloid DC subfractions. The current study suggests that in HIV-1-infected individuals treated with suppressive HAART, peripheral blood DCs do not carry HIV-1 proviral DNA or viral particles attached to their surface. These populations of peripheral blood DCs are likely not a major HIV-1 reservoir in patients on HAART with clinically undetectable plasma viral RNA.

Oral epithelial cells are susceptible to cell-free and cell-associated HIV-1 infection in vitro

Epithelial cells lining the oral cavity are exposed to HIV-1 through breast-feeding and oral-genital contact. Genital secretions and breast milk of HIV-1-infected subjects contain both cell-free and cell-associated virus. To determine if oral epithelial cells can be infected with HIV-1 we exposed gingival keratinocytes and adenoid epithelial cells to cell-free virus and HIV-1-infected peripheral blood mononuclear cells and monocytes. Using primary isolates we determined that gingival keratinocytes are susceptible to HIV-1 infection via cell-free CD4-independent infection only. R5 but not X4 viral strains were capable of infecting the keratinocytes. Further, infected cells were able to release infectious virus. In addition, primary epithelial cells isolated from adenoids were also susceptible to infection; both cell-free and cell-associated virus infected these cells. These data have potential implications in the transmission of HIV-1 in the oral cavity.

DC-SIGN: a novel HIV receptor on DCs that mediates HIV-1 transmission

The dendritic cell (DC)-specific HIV-1 receptor DC-SIGN plays a key-role in the dissemination of HIV-1 by DCs. DC-SIGN captures HIV-1 at sites of entry, enabling its transport to lymphoid tissues, where DC-SIGN efficiently transmits low amounts of HIV-1 to T cells. The expression pattern of DC-SIGN in mucosal tissue, lymph nodes, placenta and blood suggests a function for DC-SIGN in both horizontal and vertical transmission of HIV-1. Moreover, the efficiency of DC-SIGN+ blood DC to transmit HIV-1 to T cells supports a role in HIV-1 transmission via blood. To date, DC-SIGN represents a novel class of HIV-1 receptor, because it does not allow viral infection but binds HIV-1 and enhances its infection of T cells in trans. Its unique function is further underscored by its restricted expression on DCs. Although DC-SIGN is a C-type lectin with an affinity for carbohydrates exemplified by its interaction with its immunological ligand ICAM-3, recent evidence demonstrates that glycosylation of gp120 is not necessary for its interaction with DC-SIGN. Moreover, mutational analysis demonstrates that the HIV-1 gp120 binding site in DC-SIGN is different from that of ICAM-3. Besides its role in DC-mediated adhesion processes, DC-SIGN also functions as an antigen receptor that captures and internalises antigens for presentation by DC. Strikingly, HIV-1 circumvents processing after binding DC-SIGN and remains infectious for several days after capture. A better understanding of the action of this novel HIV receptor in initial viral infection and subsequent transmission will provide a basis for the design of drugs that inhibit or alter interactions of DC-SIGN with gp120, interfering with HIV-1 dissemination and that may have a therapeutic value in both immunological diseases and/or HIV-1 infections.

The role of dendritic cells in the pathogenesis of HIV-1 infection

Dendritic cells are professional antigen-presenting cells required for generation of adaptive immunity. These cells are one of the initial target cells for HIV-1 infection or capture of virions at site of transmission in the mucosa. DCs carrying HIV-1 will migrate to the lymphoid tissue where they can contribute to the dissemination of the virus to adjacent CD4+ T cells. In addition, HIV-1-exposed DCs may have impaired antigen-presenting capacity resulting in inadequate expansion of HIV-1-specific T cell responses. Here, we review the infection of different subtypes of DCs by HIV-1 and the relevance of these cells in the transmission and establishment of HIV-1 disease. In addition, we discuss the mechanisms through which HIV-1-DC interactions could be exploited to optimise the generation and maintenance of HIV-1-specific T cell immunity.

Dendritic cells from CML patients have altered actin organization, reduced antigen processing, and impaired migration

Chronic myeloid leukemia (CML) is characterized by expression of the BCR-ABL fusion gene that encodes a 210-kDa protein, which is a constitutively active tyrosine kinase. At least 70% of the oncoprotein is localized to the cytoskeleton, and several of the most prominent tyrosine kinase substrates for p210(BCR-ABL) are cytoskeletal proteins. Dendritic cells (DCs) are bone marrow-derived antigen-presenting cells responsible for the initiation of immune responses. In CML patients, up to 98% of myeloid DCs generated from peripheral blood mononuclear cells are BCR-ABL positive. In this study we have compared the morphology and behavior of myeloid DCs derived from CML patients with control DCs from healthy individuals. We show that the actin cytoskeleton and shape of CML-DCs of myeloid origin adherent to fibronectin differ significantly from those of normal DCs. CML-DCs are also defective in processing and presentation of exogenous antigens such as tetanus toxoid. The antigen-processing defect may be a consequence of the reduced capacity of CML-DCs to capture antigen via macropinocytosis or via mannose receptors when compared with DCs generated from healthy individuals. Furthermore, chemokine-induced migration of CML-DCs in vitro was significantly reduced. These observations cannot be explained by a difference in the maturation status of CML and normal DCs, because phenotypic analysis by flow cytometry showed a similar surface expression of maturation makers. Taken together, these results suggest that the defects in antigen processing and migration we have observed in CML-DCs may be related to underlying cytoskeletal changes induced by the p210(BCR-ABL) fusion protein.

Mobilization of dendritic cells in cancer patients treated with granulocyte colony-stimulating factor and chemotherapy

The number of dendritic cells (DC) circulating in the peripheral blood of cancer patients were monitored at multiple time points during chemotherapy and granulocyte colony-stimulating factor (G-CSF) support. DC were identified via the lack of expression of standard lineage markers and high expression of HLA-DR (LN-/DR+). The expression of DC-associated markers, including CD83, CD11c, IL-3Ralpha (CDw123) and CD86, within this LN-/DR+ population was also monitored. Maximal mobilization occurred during recovery on d 12, with a mean 32-fold increase in LN-/DR+ numbers. The most striking increase was observed in the LN-/DR+/CD83+ cell population: 12 d after commencement of treatment, the proportion of these cells had increased by approximately 120-fold when compared with baseline. Peripheral blood mononuclear cell (PBMC) and CD34+ cell numbers also peaked 12 d into the treatment regimen in most patients. These data suggest that it should be possible to acquire substantial numbers of DC from leukapheresis products collected from cancer patients undergoing a standard treatment regimen of chemotherapy and G-CSF. This strategy may be a feasible, low-risk means of acquiring cells for DC-based vaccine studies.

Distribution and immunophenotype of DC-SIGN-expressing cells in SIV-infected and uninfected macaques

DC-SIGN (dendritic cell-specific ICAM-3 grabbing nonintegrin), an external C-type lectin expressed on dendritic cells (DCs), has been proposed to play a pivotal role in trafficking HIV/SIV from mucosal surfaces to lymphoid tissues. Although the location of DC-SIGN expression has been established in a limited number of human tissues, its distribution in the rhesus macaque has not yet been determined. This study characterized the distribution and immunophenotype of DC-SIGN-expressing cells in SIV-infected and uninfected macaque tissues by immunohistochemistry (IHC) and confocal microscopy. IHC, using monoclonal and polyclonal antibodies against DC-SIGN, was performed on a variety of tissues. To further define the immunophenotype of DC-SIGN(+) cells, double-labeling with antibodies to CD68, fascin, and HLA-DR was done. In both infected and uninfected macaques, DC-SIGN(+) cells were located within the submucosa and lamina propria of tongue, vagina, rectum, and tonsil; however, no positive cells were present within the epithelium of any tissue. Antibodies to DC-SIGN also labeled Kupffer cells within the liver and scattered perivascular cells in the brain. Within lymph nodes, numerous positive cells were present within sinusoids in addition to cells consistent with interdigitating reticular cells in the paracortex and scattered follicular dendritic cells within germinal centers. In spleen of uninfected macaques, there was a similar distribution of DC-SIGN(+) cells with sinusoidal, marginal zone, and interdigitating dendritic cells staining; however, there was a marked paucity of staining in the spleens of SIV-infected macaques. DC-SIGN(+) cells were consistently CD68(+), but fascin(-) and HLA-DR(-). The absence of intraepithelial DC-SIGN-positive cells in mucosal tissues suggests that DC-SIGN does not play a significant role in transmucosal passage of HIV/SIV.

Suppression of clonogenic potential of human bone marrow mesenchymal stem cells by HIV type 1: putative role of HIV type 1 tat protein and inflammatory cytokines

Bone marrow abnormalities are frequently observed in HIV-1-infected individuals. Infection of marrow mesenchymal stem cells (MSCs) may abrogate their growth properties and hematopoietic supportive functions. To delineate the cell type infected, and factors responsible for the deleterious effects, human bone marrow cells were exposed to HIV-1 in vitro. By week 4, the ability of MSCs to form colonies of purely fibroblasts (CFU-F) and mixed colonies of fibroblasts and adipocytes (CFU-FA) was suppressed by 23 +/- 5 and 55 +/- 7%, respectively. The p24 concentration in culture supernatants steadily declined from 170 ng/ml in the inoculum to 134 +/- 30, 35 +/- 15, 2.3 +/- 3, and <0.02 ng/ml at the end of week 1, 2, 3, and 4, respectively. However, even at week 4, coculturing with MT-4 lymphocytes for 1 week dramatically increased p24 levels. Polymerase chain reaction (PCR) amplification, using HIV-1-specific primers, and in situ hybridization with an HIV-1 cDNA probe demonstrated the presence of virus-specific nucleic acids within stromal colonies. Coimmunostaining with antibody to CD83 implicated the presence of HIV-1 within dendritic progenitor cells. Immunostaining with HIV-1 Tat antibody demonstrated the presence of Tat protein and reverse transcriptase (RT)-PCR assays showed increased (160-220%) mRNA levels for inflammatory cytokines (tumor necrosis factor alpha [TNF-alpha], interleukin 1beta [IL-1beta], IL-6, and macrophage inflammatory protein 1alpha [MIP-1alpha]). A concentration-dependent decrease in CFU-STROs was observed on incubation with either Tat protein (1-100 ng/ml) or with TNF-alpha or IL-1beta (0.025-25 ng/ml). These results suggest that HIV-1 infection of stromal cells may produce inhibitory factors that suppress the clonogenic potential of MSCs.

Subset of DC-SIGN(+) dendritic cells in human blood transmits HIV-1 to T lymphocytes

The dendritic cell (DC)-specific molecule DC-SIGN is a receptor for the HIV-1 envelope glycoprotein gp120 and is essential for the dissemination of HIV-1. DC-SIGN is expressed by DCs, both monocyte-derived DCs and DCs in several tissues, including mucosa and lymph nodes. To identify a DC-SIGN(+) DC in blood that may be involved in HIV-1 infection through blood, we have analyzed the expression of DC-SIGN in human blood cells. Here we describe the characterization of a subset of DCs in human blood, isolated from T-/NK-/B-cell-depleted peripheral blood mononuclear cells (PBMCs) on the basis of expression of DC-SIGN. This subset coexpresses CD14, CD16, and CD33 and is thus of myeloid origin. In contrast to CD14(+) monocytes, DC-SIGN(+) blood cells display a DC-like morphology and express markers of antigen-presenting cells, including CD1c, CD11b, CD11c, CD86, and high levels of major histocompatibility complex (MHC) class I and II molecules. This DC population differs from other described CD14(-) blood DC subsets. Functionally, DC-SIGN(+) blood DCs are able to stimulate proliferation of allogeneic T cells and can produce tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) upon activation with lipopolysaccharide (LPS). When they encounter HIV-1, low amounts of these blood DC-SIGN(+) DCs enhance infection of T lymphocytes in trans, whereas blood monocytes and CD14(-) blood DCs are not capable of transmitting HIV-1. Therefore DC-SIGN(+) blood DCs can be the first target for HIV-1 upon transmission via blood; they can capture minute amounts of HIV-1 through DC-SIGN and transfer HIV-1 to infect target T cells in trans.

Differential transmission of human immunodeficiency virus type 1 by distinct subsets of effector dendritic cells

Dendritic cells (DC) support human immunodeficiency virus type 1 (HIV-1) transmission by capture of the virus particle in the mucosa and subsequent transport to the draining lymph node, where HIV-1 is presented to CD4(+) Th cells. Virus transmission involves a high-affinity interaction between the DC-specific surface molecule DC-SIGN and the viral envelope glycoprotein gp120 and subsequent internalization of the virus, which remains infectious. The mechanism of viral transmission from DC to T cells is currently unknown. Sentinel immature DC (iDC) develop into Th1-promoting effector DC1 or Th2-promoting DC2, depending on the activation signals. We studied the ability of these effector DC subsets to support HIV-1 transmission in vitro. Compared with iDC, virus transmission is greatly upregulated for the DC1 subset, whereas DC2 cells are inactive. Increased transmission by DC1 correlates with increased expression of ICAM-1, and blocking studies confirm that ICAM-1 expression on DC is important for HIV transmission. The ICAM-1-LFA-1 interaction is known to be important for immunological cross talk between DC and T cells, and our results indicate that this cell-cell contact is exploited by HIV-1 for efficient transmission.

Overexpression, purification, and biochemical characterization of the extracellular human CD83 domain and generation of monoclonal antibodies

CD83 is a 45-kDa glycoprotein and member of the immunoglobulin (Ig) superfamily. It is the best known marker for mature dendritic cells. Although the precise function of CD83 is not known, its selective expression and upregulation together with the costimulators CD80 and CD86 suggests an important role of CD83 in the induction of immune responses. To perform functional studies and to elucidate its mode of action it is vital to obtain recombinant expressed and highly purified CD83 molecules. Therefore, the external Ig domain of human CD83 (hCD83ext) was expressed as a GST fusion protein (GST-hCD83ext) and the soluble protein was purified under native conditions. The fusion protein was purified using GSTrap columns followed by anion-exchange chromatography. GST-hCD83ext was then cleaved using thrombin and soluble hCD83ext was further purified using GSTrap columns and finally by a preparative gel filtration as a polishing step and used for further characterization. The purified GST-hCD83 fusion protein was also used to generate monoclonal anti-CD83 antibodies in a rat system. Two different monoclonal antibodies were generated. Using these antibodies, CD83 was specifically recognized in FACS and Western blot analyses. Furthermore, we showed that native CD83 is glycosylated and that this glycosylation influences the binding of the antibodies in Western blot analyses. Finally, the purified hCD83ext protein was analyzed by one-dimensional NMR and these analyses strongly indicate that hCD83ext is folded and could therefore be used for further structural and functional studies.

Identification of different binding sites in the dendritic cell-specific receptor DC-SIGN for intercellular adhesion molecule 3 and HIV-1

The novel dendritic cell (DC)-specific human immunodeficiency virus type 1 (HIV-1) receptor DC-SIGN plays a key role in the dissemination of HIV-1 by DC. DC-SIGN is thought to capture HIV-1 at mucosal sites of entry, facilitating transport to lymphoid tissues, where DC-SIGN efficiently transmits HIV-1 to T cells. DC-SIGN is also important in the initiation of immune responses by regulating DC-T cell interactions through intercellular adhesion molecule 3 (ICAM-3). We have characterized the mechanism of ligand binding by DC-SIGN and identified the crucial amino acids involved in this process. Strikingly, the HIV-1 gp120 binding site in DC-SIGN is different from that of ICAM-3, consistent with the observation that glycosylation of gp120, in contrast to ICAM-3, is not crucial to the interaction with DC-SIGN. A specific mutation in DC-SIGN abrogated ICAM-3 binding, whereas the HIV-1 gp120 interaction was unaffected. This DC-SIGN mutant captured HIV-1 and infected T cells in trans as efficiently as wild-type DC-SIGN, demonstrating that ICAM-3 binding is not necessary for HIV-1 transmission. This study provides a basis for the design of drugs that inhibit or alter interactions of DC-SIGN with gp120 but not with ICAM-3 or vice versa and that have a therapeutic value in immunological diseases and/or HIV-1 infections.

CD83 expression influences CD4+ T cell development in the thymus

T lymphocyte selection and lineage commitment in the thymus requires multiple signals. Herein, CD4+ T cell generation required engagement of CD83, a surface molecule expressed by thymic epithelial and dendritic cells. CD83-deficient (CD83-/-) mice had a specific block in CD4+ single-positive thymocyte development without increased CD4+CD8+ double- or CD8+ single-positive thymocytes. This resulted in a selective 75%-90% reduction in peripheral CD4+ T cells, predominantly within the naive subset. Wild-type thymocytes and bone marrow stem cells failed to differentiate into mature CD4+ T cells when transferred into CD83-/- mice, while CD83-/- thymocytes and stem cells developed normally in wild-type mice. Thereby, CD83 expression represents an additional regulatory component for CD4+ T cell development in the thymus.

The extracellular domain of CD83 inhibits dendritic cell-mediated T cell stimulation and binds to a ligand on dendritic cells

CD83 is an immunoglobulin (Ig) superfamily member that is upregulated during the maturation of dendritic cells (DCs). It has been widely used as a marker for mature DCs, but its function is still unknown. To approach its potential functional role, we have expressed the extracellular Ig domain of human CD83 (hCD83ext) as a soluble protein. Using this tool we could show that immature as well as mature DCs bind to CD83. Since CD83 binds a ligand also expressed on immature DCs, which do not express CD83, indicates that binding is not a homophilic interaction. In addition we demonstrate that hCD83ext interferes with DC maturation downmodulating the expression of CD80 and CD83, while no phenotypical effects were observed on T cells. Finally, we show that hCD83ext inhibits DC-dependent allogeneic and peptide-specific T cell proliferation in a concentration dependent manner in vitro. This is the first report regarding functional aspects of CD83 and the binding of CD83 to DCs.

DC-SIGN interactions with human immunodeficiency virus: virus binding and transfer are dissociable functions

The C-type lectins DC-SIGN and DC-SIGNR capture and transfer human immunodeficiency virus (HIV) to susceptible cells, although the underlying mechanism is unclear. Here we show that DC-SIGN/DC-SIGNR-mediated HIV transmission involves dissociable binding and transfer steps, indicating that efficient virus transmission is not simply due to tethering of virus to the cell surface.

HIV-1 infection of placental cord blood monocyte-derived dendritic cells

Dendritic cells (DC), the most potent antigen-presenting cells (APC), have been implicated as the initial targets of HIV infection in skin and mucosal surfaces. DC can be generated in vitro from blood-isolated CD14(+) monocytes or CD34(+) hematopoietic progenitor cells in the presence of various cytokines. In this study, we investigated whether monocytes obtained from placental cord blood are capable of differentiation into dendritic cells when cultured with a combination of cytokines - granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-4 (IL-4), and tumor necrosis factor-alpha (TNF-alpha). We then examined HIV infection, HIV receptor (CD4, CCR5) expression, and beta-chemokine [macrophage inflammatory protein-1alpha and -1beta (MIP-1alpha, MIP-1beta)] production by placental cord monocyte-derived dendritic cells (MDDC) as compared to that of autologous cord monocyte-derived macrophages (MDM). Monocytes isolated from placental cord blood differentiate into DC after 7 days in culture with the mixture of cytokines, as demonstrated by development of characteristic DC morphology, loss of CD14 expression, and gain of CD83, a marker for mature DC. Mature cord MDDC had significantly lower susceptibility to M-tropic ADA (CCR5-dependent) envelope-pseudotyped HIV infection in comparison to autologous placental cord MDM, whereas there was no significant difference in virus replication in cord MDDC and MDM infected with murine leukemia virus envelope-pseudotyped HIV (HIV receptor-independent). This limited susceptibility of cord MDDC to M-tropic HIV infection may be due to lower expression of CD4 and CCR5 on the cell membrane and higher production of MIP-1alpha and MIP-1beta. These data provide important information toward our understanding of the biological properties of cord MDDC in relation to HIV infection.

Dendritic cells and viral immunity: friends or foes?

Dendritic cells (DC) residing in epithelial tissues of various mucosae and the skin are characterized by the unique ability to capture antigens and migrate to draining lymph nodes, where they can activate naive and memory T cells. Although DC play a pivotal role in inducing protective immunity to viral infection, they can also be exploited by viruses to evade the host immune response, induce immune suppression, or serve as latent viral reservoirs. Thus, virus interactions with DC may lead to an immune response that can be protective, but does not necessarily lead to complete virus elimination, resulting in immunopathology.

A soluble form of CD83 is released from activated dendritic cells and B lymphocytes, and is detectable in normal human sera

CD83 is an inducible glycoprotein expressed predominantly by dendritic cells (DC) and B lymphocytes. Expression of membrane CD83 (mCD83) is widely used as a marker of differentiated/activated DC but its function and ligand(s) are presently unknown. We report the existence of a soluble form of CD83 (sCD83). Using both a sCD83-specific ELISA and Western blotting, we could demonstrate the release of sCD83 by mCD83(+) B cell and Hodgkin's disease-derived cell lines, but not mCD83(-) cells. Inhibition of de novo protein synthesis did not affect the release of sCD83 during short-term (2 h) culture of cell lines although mCD83 expression was significantly reduced, suggesting sCD83 is generated by the release of mCD83. Isolated tonsillar B lymphocytes and monocyte-derived DC, which are mCD83(low), released only low levels of sCD83 during culture. However, the differentiation/activation of these populations both up-regulated mCD83 and increased sCD83 release significantly. Analysis of sera from normal donors demonstrated the presence of low levels (121 +/- 3.6 pg/ml) of circulating sCD83. Further studies utilizing purified sCD83 and the analysis of sCD83 levels in disease may provide clues to the function and ligand(s) of CD83.

Postentry restriction to human immunodeficiency virus-based vector transduction in human monocytes

Cells of the monocyte lineage can be infected with human immunodeficiency virus type 1 (HIV-1) both during clinical infection and in vitro. The ability of HIV-1-based vectors to transduce human monocytes, monocyte-derived macrophages, and dendritic cells (DCs) was therefore examined, in order to develop an efficient protocol for antigen gene delivery to human antigen-presenting cells. Freshly isolated monocytes were refractory to HIV-1-based vector transduction but became transducible after in vitro differentiation to mature macrophages. This maturation-dependent transduction was independent of the HIV-1 accessory proteins Vif, Vpr, Vpu, and Nef in the packaging cells and of the central polypurine tract in the vector, and it was also observed with a vesicular stomatitis virus-pseudotyped HIV-1 provirus, defective only in envelope and Nef. The level and extent of reverse transcription of the HIV-1-based vector was similar after infection of immature monocytes and of mature macrophages. However, 2LTR vector circles could not be detected in monocytes, suggesting a block to vector nuclear entry in these cells. Transduction of freshly isolated monocytes exposed to HIV-1-based vector could be rescued by subsequent differentiation into DCs. This rescue was induced by fetal calf serum in the DC culture medium, which promoted vector nuclear entry.

Uptake of HIV and latex particles by fresh and cultured dendritic cells and monocytes

Blood dendritic cells (DC) efficiently carry HIV-1 and transmit infection to CD4+ T cells in the absence of productive infection of the APC. Fluorescent latex beads were used to define the endocytic pathways that may contribute to this non-infectious pathway of virus carriage. Beads between 14 nm and 2300 nm in diameter were taken up by uncultured blood DC, but uptake of beads larger than 280 nm was much reduced in the DC compared to monocytes. After culture, there was a reduction in bead carriage in DC compared to monocytes. In the DC, beads were found as small aggregates in class II containing compartments or as single beads just below the cell surface. Beads accumulated in monocytes as aggregates in class II negative compartments. Bead recycling occurred in DC, but not in the fresh or cultured monocytes. Electron microscopy of HIV-1-pulsed DC cultured with CD4+ T cells showed accumulation of apoptotic debris and virions within endosomes in the DC. The peripheral location and recycling of endocytosed material in DC provides a pathway for virion transfer from DC to T cells that does not occur in monocytes.

DC-SIGN, a dentritic cell-specific HIV-1 receptor present in placenta that infects T cells in trans-a review

Dendritic cells (DC) capture micro-organisms that enter peripheral mucosal tissues and then migrate to secondary lymphoid organs, where they present in antigenic form to resting T cells and thus initiate adaptive immune responses. Here we describe the properties of a DC-specific C-type lectin, DC-SIGN, that is highly expressed on DC present in mucosal tissues and binds to the HIV-1 envelope glycoprotein gp120. DC-SIGN does not function as a receptor for viral entry into DC, but instead promotes efficient infection in trans of cells that express CD4 and chemokine receptors. The interaction of DC-SIGN with HIV gp120 may be an important target for therapeutic intervention and vaccine development.

Changes in dendritic cell subsets in the lymph nodes of rhesus macaques after application of glucocorticoids

Corticosteroids are used therapeutically as potent immunosuppressive and antiinflammatory drugs for a broad spectrum of diseases. Although corticosteroids are known to inhibit the production of many cytokines in activated T cells, there is also evidence for increases in IL-4 and in some cases IFNgamma production. These conflicting results may be caused by contrary effects of corticosteroids on different cell types involved in immune regulation, for instance antigen presenting cells (APC) versus T cells. In the present study we simultaneously investigated the effect of local as well as systemic application of glucocorticoids (GCC) on the phenotype of APC in the skin as well as the lymph nodes in a model primate species, the rhesus macaque. Using a range of APC markers, including CD68, HAM56, HLA-DR, CD1a, p55, RFD-1, and costimulatory molecules CD40, CD80, and CD86 we document the close phenotypic resemblance of rhesus and human APC. We noted that topical GCC treatment specifically lead to a marked decrease in the number of CD1a expressing cells in the draining lymph nodes. However, the number of CD1a positive cells in peripheral lymph nodes was not affected by systemic GCC treatment. Importantly, by performing double staining of CD1a with RFD-1 we observed a shift in the expression pattern of these dendritic cell markers in the lymph nodes, with an increase in the number of RFD-1 single positive cells relative to CD1a single positive and CD1a/RFD-1 double positive cells. These findings suggest that GCC treatment results in the presence of phenotypically more mature APC.

DC-SIGNR, a DC-SIGN homologue expressed in endothelial cells, binds to human and simian immunodeficiency viruses and activates infection in trans

DC-SIGN, a C-type lectin expressed on the surface of dendritic cells (DCs), efficiently binds and transmits HIVs and simian immunodeficiency viruses to susceptible cells in trans. A DC-SIGN homologue, termed DC-SIGNR, has recently been described. Herein we show that DC-SIGNR, like DC-SIGN, can bind to multiple strains of HIV-1, HIV-2, and simian immunodeficiency virus and transmit these viruses to both T cell lines and human peripheral blood mononuclear cells. Binding of virus to DC-SIGNR was dependent on carbohydrate recognition. Immunostaining with a DC-SIGNR-specific antiserum showed that DC-SIGNR was expressed on sinusoidal endothelial cells in the liver and on endothelial cells in lymph node sinuses and placental villi. The presence of this efficient virus attachment factor on multiple endothelial cell types indicates that DC-SIGNR could play a role in the vertical transmission of primate lentiviruses, in the enabling of HIV to traverse the capillary endothelium in some organs, and in the presentation of virus to CD4-positive cells in multiple locations including lymph nodes.