Relative efficacy of human monocytes and dendritic cells as accessory cells for T cell replication

The discovery of dendritic cells

An excerpt from Ralph Steinman’s Harvey Lecture describing the discovery of dendritic cells.

Monocyte-Derived Dendritic Cells Promote Th Polarization, whereas Conventional Dendritic Cells Promote Th Proliferation

Monocyte-derived dendritic cells (moDCs) dramatically increase in numbers upon infection and inflammation; accordingly, we found that this also occurs during allogeneic responses. Despite their prominence, how emergent moDCs and resident conventional DCs (cDCs) divide their labor as APCs remain undefined. Hence, we compared both direct and indirect presentation by murine moDCs versus cDCs. We found that, despite having equivalent MHC class II expression and in vitro survival, moDCs were 20-fold less efficient than cDCs at inducing CD4(+) T cell proliferation through both direct and indirect Ag presentation. Despite this, moDCs were more potent at inducing Th1 and Th17 differentiation (e.g., 8-fold higher IFN-γ and 2-fold higher IL-17A in T cell cocultures), whereas cDCs induced 10-fold higher IL-2 production. Intriguingly, moDCs potently reduced the ability of cDCs to stimulate T cell proliferation in vitro and in vivo, partially through NO production. We surmise that such division of labor between moDCs and cDCs has implications for their respective roles in the immune response.

Perspectives on antigen presenting cells in zebrafish

Antigen presentation is a critical step in the activation of naïve T lymphocytes. In mammals, dendritic cells (DCs), macrophages, and B lymphocytes can all function as antigen presenting cells (APCs). Although APCs have been identified in zebrafish, it is unclear if they fulfill similar roles in the initiation of adaptive immunity. Here we review the characterization of zebrafish macrophages, DCs, and B cells and evidence of their function as true APCs. Finally, we discuss the conservation of APC activity in vertebrates and the use of zebrafish to provide a new perspective on the evolution of these functions.

Two functionally distinct myeloid dendritic cell subpopulations are present in bovine blood

Immature myeloid (m)DCs circulating in the blood of cattle have been defined as lineage negative (Lin(-))MHCII(+)CD11c(+)CD205(+) cells. Lin(-)MHCII(+)CD11c(+)CD205(+) mDCs (0.2% blood mononuclear cells) isolated from bovine blood were heterogeneous in cell size and CD205 expression. Using highspeed cell sorting, Lin(-)MHCII(+)CD11c(+)CD205(+) DCs were sorted into CD205(Hi) and CD205(Lo) subpopulations which were phenotypically distinct and differed significantly (P<0.01) in TLR gene expression. CD205(Hi) and CD205(Lo) mDCs were more efficient in macropinocytosis than monocytes and expressed no or little detectable non-specific esterase activity. CD205(Lo) mDCs efficiently activated purified allogeneic T cells and the addition of TLR agonists did not significantly alter this antigen presentation capacity. T cell activation by CD205(Lo) mDCs was associated with differential up-regulation of CD40, CD80, CD86 and TGFβ1 gene expression when compared to CD205(Hi) mDCs. In conclusion, two phenotypically and functionally distinct CD11c(+)CD205(+) mDCs were isolated from blood that had an equal capacity to acquire antigen but markedly different capacities to activate T cells.

GM-CSF-responsive monocyte-derived dendritic cells are pivotal in Th17 pathogenesis

Although multiple dendritic cell (DC) subsets have the potential to induce Th17 differentiation in vitro, the key DC that is critical in Th17 induction and Th17-mediated disease remains moot. In this study, we revealed that CCR2(+) monocyte-derived DCs (moDCs), but not conventional DCs, were critical for in vivo Th17 induction and autoimmune inflammation. Functional comparison in vitro indicated that moDCs are the most potent type of Th17-inducing DCs compared with conventional DCs and plasmacytoid DCs. Furthermore, we demonstrated that the importance of GM-CSF in Th17 induction and Th17-mediated disease is its endowment of moDCs to induce Th17 differentiation in vivo, although it has little effect on moDC numbers. Our findings identify the in vivo cellular targets that can be selectively manipulated to ameliorate Th17-mediated inflammatory diseases, as well as the mechanism of GM-CSF antagonism in such diseases.

Monocytes are essential for the neuroprotective effect of human cord blood cells following middle cerebral artery occlusion in rat

Systemic administration of human umbilical cord blood (HUCB) mononuclear cells (MNC) following middle cerebral artery occlusion (MCAO) in the rat reduces infarct size and, more importantly, restores motor function. The HUCB cell preparation is composed of immature T-cells, B-cells, monocytes and stem cells. In this study we examined whether the beneficial effects of HUCB injection were attributable to one of these cell types. Male Sprague Dawley rats underwent permanent MCAO followed 48 h later by intravenous administration of HUCB MNC preparations depleted of either CD14(+) monocytes, CD133(+) stem cells, CD2(+) T-cells or CD19(+) B cells. Motor function was measured prior to MCAO and 30 days post-stroke. When CD14(+) monocytes were depleted from the HUCB MNC, activity and motor asymmetry were similar to the MCAO only treated animals. Monocyte depletion prevented HUCB cell treatment from reducing infarct size while monocyte enrichment was sufficient to reduce infarct size. Administration of monocyte-depleted HUCB cells did not suppress Iba1 labeling of microglia in the infarcted area relative to treatment with the whole HUCB preparation. These data demonstrate that the HUCB monocytes provide the majority of the efficacy in reducing infarct volume and promoting functional recovery.

Toward a Network Model of MHC Class II-Restricted Antigen Processing

The standard model of Major Histocompatibility Complex class II (MHCII)-restricted antigen processing depicts a straightforward, linear pathway: internalized antigens are converted into peptides that load in a chaperone dependent manner onto nascent MHCII in the late endosome, the complexes subsequently trafficking to the cell surface for recognition by CD4(+) T cells (TCD4+). Several variations on this theme, both moderate and radical, have come to light but these alternatives have remained peripheral, the conventional pathway generally presumed to be the primary driver of TCD4+ responses. Here we continue to press for the conceptual repositioning of these alternatives toward the center while proposing that MHCII processing be thought of less in terms of discrete pathways and more in terms of a network whose major and minor conduits are variable depending upon many factors, including the epitope, the nature of the antigen, the source of the antigen, and the identity of the antigen-presenting cell.

Flt3 signaling-dependent dendritic cells protect against atherosclerosis

Early events in atherosclerosis occur in the aortic intima and involve monocytes that become macrophages. We looked for these cells in the steady state adult mouse aorta, and surprisingly, we found a dominance of dendritic cells (DCs) in the intima. In contrast to aortic adventitial macrophages, CD11c(+)MHC II(hi) DCs were poorly phagocytic but were immune stimulatory. DCs were of two types primarily: classical Flt3-Flt3L signaling-dependent, CD103(+)CD11b(-) DCs and macrophage-colony stimulating factor (M-CSF)-dependent, CD14(+)CD11b(+)DC-SIGN(+) monocyte-derived DCs. Both types expanded during atherosclerosis. By crossing Flt3(-/-) to Ldlr(-/-) atherosclerosis-prone mice, we developed a selective and marked deficiency of classical CD103(+) aortic DCs, and they were associated with exacerbated atherosclerosis without alterations in blood lipids. Concomitantly, the Flt3(-/-)Ldlr(-/-) mice had fewer Foxp3(+) Treg cells and increased inflammatory cytokine mRNAs in the aorta. Therefore, functional DCs are dominant in normal aortic intima and, in contrast to macrophages, CD103(+) classical DCs are associated with atherosclerosis protection.

Decisions about dendritic cells: past, present, and future

A properly functioning adaptive immune system signifies the best features of life. It is diverse beyond compare, tolerant without fail, and capable of behaving appropriately with a myriad of infections and other challenges. Dendritic cells are required to explain how this remarkable system is energized and directed. I frame this article in terms of the major decisions that my colleagues and I have made in dendritic cell science and some of the guiding themes at the time the decisions were made. As a result of progress worldwide, there is now evidence of a central role for dendritic cells in initiating antigen-specific immunity and tolerance. The in vivo distribution and development of a previously unrecognized white cell lineage is better understood, as is the importance of dendritic cell maturation to link innate and adaptive immunity in response to many stimuli. Our current focus is on antigen uptake receptors on dendritic cells. These receptors enable experiments involving selective targeting of antigens in situ and new approaches to vaccine design in preclinical and clinical systems.

Altered monocyte-derived dendritic cell function in patients on hemodialysis: a culprit for underlying impaired immune responses

BACKGROUND

Patients with end-stage renal disease (ESRD) are known to have impaired immune function. Dendritic cells (DCs) are the major antigen-presenting cells that initiate primary immune responses, linking innate and adaptive immunity. Although suboptimal immune responses to vaccination, as frequently observed in ESRD patients, might suggest the presence of impaired DC function, the precise nature of altered DC function is not fully understood.

METHODS

In the current study, we compared the maturation status, viability, and function of monocyte-derived DCs (moDCs) of patients on hemodialysis (HD) with healthy controls.

RESULTS

Surface expression of major histocompatibility complex class II, CD83, and CD86, and chemokine receptor CCR7 in moDCs was not different between HD patients and healthy controls. No significant difference was detected in the viability of moDCs determined by expression of annexin V and propidium iodide between two groups. However, moDCs from HD patients produced significantly higher amounts of IL-6 when stimulated by cytokine cocktails compared to healthy controls. In addition, mature moDCs from HD patients showed significantly enhanced allogeneic T-cell proliferation compared to healthy controls.

CONCLUSIONS

Our data demonstrate aberrant DC function in HD patients and suggest that this might contribute to impaired immune responses.

Blood monocytes: development, heterogeneity, and relationship with dendritic cells

Monocytes are circulating blood leukocytes that play important roles in the inflammatory response, which is essential for the innate response to pathogens. But inflammation and monocytes are also involved in the pathogenesis of inflammatory diseases, including atherosclerosis. In adult mice, monocytes originate in the bone marrow in a Csf-1R (MCSF-R, CD115)-dependent manner from a hematopoietic precursor common for monocytes and several subsets of macrophages and dendritic cells (DCs). Monocyte heterogeneity has long been recognized, but in recent years investigators have identified three functional subsets of human monocytes and two subsets of mouse monocytes that exert specific roles in homeostasis and inflammation in vivo, reminiscent of those of the previously described classically and alternatively activated macrophages. Functional characterization of monocytes is in progress in humans and rodents and will provide a better understanding of the pathophysiology of inflammation.

CCH cells are potent stimulators in the allogeneic mixed leucocyte reaction

Canine cutaneous histiocytoma (CCH) has been identified as a tumour of epidermal Langerhans cells (LCs) on the basis of immunophenotypic studies. Neoplastic Langerhans cells (CCH-LCs) were isolated from lesions of canine cutaneous histiocytoma. The CCH-LC cells expressed CD1b, CD11/18, CD45, MHC-I, and MHC-II. The CCH-LC cells were potent stimulators of the mixed leucocyte reaction (MLR) in vitro when compared to PBMCs from the tumour-bearing animals. This provides evidence that the neoplastic cells in CCH have functional as well as immunophenotypic characteristics of Langerhans cells.

A Dendritic Cell Primer for Oncology Nurses

Once believed to be part of the nervous system, dendritic cells (DCs) now are known to be potent antigen-presenting cells of the immune system. Upon capturing a foreign antigen, the immature DC matures as it travels to the T cells to activate an immune response. DCs can be categorized into two main subsets: DC1s and DC2s. DC1s, also called myeloid-related DCs, arise from early-precursor cells or monocytes and play a role in initiating immune responses against antigens such as cancer cells. Various cytokines stimulate the growth and differentiation of DCs, such as granulocyte macrophage-colony-stimulating factor. DC research is evolving rapidly as a clinical therapy; therefore, nurses should appreciate the cell's mechanisms of action.

Dendritic cells: translating innate to adaptive immunity

The innate immune system provides many ways to quickly resist infection. The two best-studied defenses in dendritic cells (DCs) are the production of protective cytokines-like interleukin (IL)-12 and type I interferons-and the activation and expansion of innate lymphocytes. IL-12 and type I interferons influence distinct steps in the adaptive immune response of lymphocytes, including the polarization of T-helper type 1 (Th1) CD4+ T cells, the development of cytolytic T cells and memory, and the antibody response. DCs have many other innate features that do not by themselves provide innate resistance but are critical for the induction of adaptive immunity. We have emphasized three intricate and innate properties of DCs that account for their sentinel and sensor roles in the immune system: (1) special mechanisms for antigen capture and processing, (2) the capacity to migrate to defined sites in lymphoid organs, especially the T cell areas, to initiate immunity, and (3) their rapid differentiation or maturation in response to a variety of stimuli ranging from Toll-like receptor (TLR) ligands to many other nonmicrobial factors such as cytokines, innate lymphocytes, and immune complexes. The combination of innate defenses and innate physiological properties allows DCs to serve as a major link between innate and adaptive immunity. DCs and their subsets contribute to many subjects that are ripe for study including memory, B cell responses, mucosal immunity, tolerance, and vaccine design. DC biology should continue to be helpful in understanding pathogenesis and protection in the setting of prevalent clinical problems.

Dendritic cells in a mature age

A common view supposes that dendritic cells (DCs) exist in two basic functional states: immature DCs induce tolerance to self, whereas mature DCs induce immunity to foreign antigens. However, the term 'mature' is often used not only functionally to designate immunogenic DCs but also as a phenotypic description of DCs expressing high levels of MHC, adhesion and co-stimulatory molecules. The recent realization that DCs can express such markers under non-immunogenic conditions raises the question of whether the two connotations of the term 'mature' should continue to be used interchangeably. Here, I discuss the origins of the maturation model and how terminology is evolving to better accommodate our current understanding of the function of DCs.

Monocytes-macrophages are a potential target in human infection with West Nile virus through blood transfusion

BACKGROUND

West Nile virus (WNV) transmission by transfusion was documented in 2002. Approximately 80 percent of WNV infections are asymptomatic and 1 percent develop severe neurological illness. In animals, Langerhans-dendritic cells support initial viral replication, followed by replication in lymphoid tissues and dissemination to organs and possibly to the CNS. The cellular tropism of WNV infection after transfusion and the particular human blood cells that sustain viral replication remain largely unknown. Whether primary monocyte-derived macrophages (MDMs) support WNV infection-replication and produce infectious virions, with an in vitro system, was investigated.

STUDY DESIGN AND METHODS

Elutriated monocytes (CD33+/CD14+) from suitable blood donors were cultured in the presence of macrophage-colony-stimulating factor, infected with WNV-NY99 at different time points, washed, and cultivated for up to 47 days. Supernatants were tested for WNV replication by TaqMan reverse transcription-polymerase chain reaction (RT-PCR), with primers for the envelope and/or 3'NC regions, and by cDNA-PCR to detect WNV minus-strand RNA and for the presence of functional virions by infectivity assays in Vero cells.

RESULTS

RT-PCR TaqMan of supernatants demonstrated productive infection of MDMs. Viral load reached 2 to 5 log above baseline in 3 to 6 days and then declined, with detectable viral replication persisting for up to 47 days. WNV minus-strand RNA was detected in Day 4 cultures, indicating active viral replication. Infected MDM cultures showed no cytopathic changes. Supernatants that were TaqMan-positive for the presence of WNV-infected Vero cells and produced cytopathic effects within 3 to 5 days of culture.

CONCLUSION

The susceptibility of monocytes-macrophages to productive infection in vitro is compatible with a potential role in initial WNV replication and propagation after transmission by transfusion.

Modification of accessory molecule signaling

The concept of costimulation, the requirement for an independent accessory cellular activation signal that supplements the signal delivered to a lymphocyte by antigen, has been a focal point of progress in understanding the regulation of the immune system. While considerable attention has been directed to new developments related to the activation of cells of the innate immune system through Toll-like receptors, resulting in the production of soluble mediators, augmented expression of cell surface costimulatory molecules on antigen-presenting cells is arguably the most significant early outcome of immune system activation. It is those cell surface molecules that provide the essential afferent costimulatory signals to T cells of the adaptive immune response. Once fully activated, T cells express their own cell surface accessory molecules that permit those T cells to instruct interacting B cells, macrophages, and dendritic cells to further implement an effective immune response. Significantly for patients with autoimmune diseases, the manipulation of costimulatory signals represents a rational and effective approach to modulating the chronic immune system activation that characterizes those diseases. Further elucidation of the complexities of members of the accessory molecule families and their functions should lead to an ever greater capacity for therapeutic modulation of the immune response in autoimmune and inflammatory diseases.

Antigen targeting to dendritic cells elicits long-lived T cell help for antibody responses

Resistance to several prevalent infectious diseases requires both cellular and humoral immune responses. T cell immunity is initiated by mature dendritic cells (DCs) in lymphoid organs, whereas humoral responses to most antigens require further collaboration between primed, antigen-specific helper T cells and naive or memory B cells. To determine whether antigens delivered to DCs in lymphoid organs induce T cell help for antibody responses, we targeted a carrier protein, ovalbumin (OVA), to DCs in the presence of a maturation stimulus and assayed for antibodies to a hapten, (4-hydroxy-3-nitrophenyl) acetyl (NP), after boosting with OVA-NP. A single DC-targeted immunization elicited long-lived T cell helper responses to the carrier protein, leading to large numbers of antibody-secreting cells and high titers of high-affinity antihapten immunoglobulin Gs. Small doses of DC-targeted OVA induced higher titers and a broader spectrum of anti-NP antibody isotypes than large doses of OVA in alum adjuvant. Similar results were obtained when the circumsporozoite protein of Plasmodium yoelii was delivered to DCs. We conclude that antigen targeting to DCs combined with a maturation stimulus produces broad-based and long-lived T cell help for humoral immune responses.

Direct allorecognition promotes activation of bystander dendritic cells and licenses them for Th1 priming: a functional link between direct and indirect allosensitization

T-cell sensitization to indirectly presented alloantigens (indirect pathway of allorecognition) plays a critical role in chronic rejection. The usual very efficient priming of such self-restricted, T helper type 1 (Th1)-deviated CD4+ T cells obviously conflicts with the fact that allogeneic MHC molecules are poorly immunogenic per se. The aim of the present study is to elucidate whether direct allosensitization induces production of inflammatory mediators that may affect recruitment and activation of immature bystander (host) dendritic cells (DC). These potential mechanisms were studied in vitro by conducting primary allogeneic mixed leucocyte reactions (MLR), mimicking the priming phase in secondary lymphoid organs, and secondary MLR, mimicking the effector phase within the graft. Primary, and particularly secondary, MLR supernatants were found to contain high levels of monocyte/immature DC-recruiting CC chemokines and pro-inflammatory cytokines. Exposure of immature DC to primary or secondary MLR supernatants was found to upregulate CD40 expression and further enhanced lipopolysaccharide-induced interleukin-12 (IL-12) p70 production. Secondary MLR supernatants additionally induced upregulation of CD86 and deviated allogeneic T-cell responses towards Th1 (enhanced interferon-gamma production without concomitant induction of detectable IL-4 or IL-10 production). These findings indicate that direct allorecognition may act as a Th1-deviating adjuvant for indirect allosensitization.

Epigenetic regulation of the dendritic cell-marker gene ADAM19

Human ADAM19 (MADDAM) is a molecular marker for human dendritic cells and not expressed in macrophages. To investigate its cell-type-specific expression, we defined the transcriptional start site and the proximal promoter. Sequence analysis of the promoter revealed putative binding sites for several transcription factors including Sp1, Sp3, NF-kappaB, and VDR. A minimal promoter construct of 150 bp showed little difference in reporter activity between macrophages and dendritic cells. Transfection of monocytic THP-1 with the 150-bp fragment also resulted in significant reporter activity, despite the lack of endogenous MADDAM expression. TSA, a known inhibitor of histone deacetylation, led to a dose-dependent induction of MADDAM mRNA in THP-1. ChIP assays demonstrated high levels of acetylated histone H3 in the proximal promoter region of the MADDAM gene in TSA-treated THP-1 cells and dendritic cells as compared to macrophages, indicating an important role of histone acetylation in the regulation of the MADDAM gene.

Comparison of CD34 and monocyte-derived dendritic cells from mobilized peripheral blood from cancer patients

Dendritic cells (DCs) are potent antigen-presenting cells that are integral to the initiation of T-cell immunity. Two cell types can be used as a source for generating DCs: monocytes and CD34(+) stem cells. Despite many investigations characterizing DCs, none have performed a direct paired comparison of monocyte and stem cell-derived DCs. Therefore, it is unclear whether one cell source has particular advantages over the other, or whether inherent differences exist between the two populations. We undertook the following study to determine if there were any differences in DCs generated from monocytes or CD34(+) cells from mobilized peripheral blood. DCs were generated by culturing the adherent cells (monocytes) in interleukin-4 and GM-CSF for 7 days, or by culturing nonadherent cells (CD34(+)) in the presence of GM-CSF and tumor necrosis factor alpha for 14 days. The resulting DCs were compared morphologically, phenotypically, functionally, and by yield. We could generate morphologically and phenotypically similar DCs. Differences were encountered when expression levels of some cell surface markers were examined (CD86, HLA-DR). There was no difference in how the DCs performed in a mixed lymphocyte reaction (p = .3). Further, no statistical difference was discovered when we examined cellular (DC) yield (p = .1); however, there was a significant difference when yield was normalized to the starting number of monocytes or CD34(+) cells (p = .016). Together, these data demonstrate that differences do exist between monocyte-derived DCs and CD34-derived DCs from the same cellular product (apheresis) from the same individual.

Validation of the COSTIM bioassay for dendritic cell potency

Dendritic cells (DCs) are increasingly prepared in vitro for use in clinical trials of human disease. Their utility in experimental immunotherapy has driven significant advances in the manufacture of these cells. Thus it has become imperative that, in concert with other quality control measures, a potency test be utilized for the GMP/GLP lot-release of DC products for preclinical and clinical studies. For this purpose we developed a novel method named the 'COSTIM bioassay', which selectively measures co-stimulatory activity, or functional potency of the DCs. In this method, T-cells stimulated with a sub-optimal amount of anti-CD3 antibody are unable to proliferate unless a source of co-stimulation (DCs) is added to the culture. We describe our validation of this method in this paper.

Site-specific regulation of tissue dendritic cell function by granulocyte-macrophage colony-stimulating-factor

Tissue dendritic cells (DC) are usually associated with phagocytic function but poor T-cell immunostimulatory capacity. Following activation, dendritic cells are stimulated to leave tissue sites and migrate to lymphoid tissue, acquiring immunostimulatory capacity during the process. We provide evidence that the immunostimulatory capacity of tissue DC, but not spleen cells, can be affected in situ by granulocyte-macrophage colony-stimulating-factor (GM-CSF). Initially it was found that islet cells from non-obese diabetic and BALB/c mice, which produce GM-CSF, showed significantly higher immunostimulatory capacity than islets from C3H and C57BL/6 mice, which do not produce GM-CSF. Second, pretreatment of nonobese diabetic mice with anti-GM-CSF antibody significantly reduced the immunostimulatory capacity of islet cells, but not spleen cells, although it had no effect on the numbers of cells expressing DC-associated antigens. Therefore the immunostimulatory function of islet DC is partially dependent on GM-CSF. By contrast, spleen DC immunostimulatory function does not show the same dependence on GM-CSF. This may affect the ability of dendritic cells to stimulate autoimmune responses or tolerance.

Lycopene suppresses the lipopolysaccharide-induced phenotypic and functional maturation of murine dendritic cells through inhibition of mitogen-activated protein kinases and nuclear factor-kappaB

Dendritic cells (DC) are the most potent of antigen-presenting cells. The most important function of DC is to initiate the immune response by presenting antigens to naïve T lymphocytes. Currently, little is known about the basic action of lycopene in murine bone marrow (BM)-derived DC. In the present study, we have revealed that lycopene significantly attenuates the phenotypic and functional maturation of murine BM-DC, especially in lipopolysaccharide-induced DC maturation. We found that lycopene down-regulates the expression of costimulatory molecules (CD80 and CD86) and major histocompatibility complex type II molecules. We also determined that lycopene-treated DC were poor stimulators of naïve allogeneic T-cell proliferation and induced lower levels of interleukin-2 in responding T cells. They also exhibited impaired interleukin-12 production. Additionally, lycopene was able to inhibit mitogen-activated protein kinases, such as ERK1/2, p38 and JNK, and the transcription factor, nuclear factor-kappaB. Assessment of the in vivo effects of lycopene may reveal an inability to induce a normal cell-mediated immune response, despite the ability of the cells to migrate to the spleen. This data provides new insight into the immunopharmacology of lycopene and suggests a novel approach to the manipulation of DC for therapeutic application.

Vitamin E-coated dialyzer membranes downregulate expression of monocyte adhesion and co-stimulatory molecules

BACKGROUND

In patients on chronic hemodialysis leukocyte activation has been related to the impaired function of the immune system. In this study we investigated if the vitamin E-coated dialyzer membrane could reduce monocyte activation thereby improving cellular immunity.

METHODS

This hypothesis was tested in a prospective crossover trial in which 14 stable hemodialysis patients were switched from the baseline hemophane dialyzer to a vitamin E-coated and thereafter a polysulphone dialyzer membrane or vice versa.

RESULTS

Monocyte MHC class I, CD54 and ICAM-1 expression was significantly downregulated when a vitamin E-coated or polysulphone dialyzer was used. The use of a vitamin E membrane specifically decreased monocyte CD40 and CD86 expression. Lectin induced T cell proliferation increased with the use of the vitamin E-coated membrane as compared to polysulphone and hemophane dialyzers.

CONCLUSION

Vitamin E-coated dialyzers induced a less-activated phenotype of monocytes and may improve cellular immunity.

Peripheral blood dendritic cells and GM-CSF as an adjuvant for hepatitis B vaccination in hemodialysis patients

BACKGROUND

Dysfunctional antigen presentation may underlie the impaired antibody response to hepatitis B vaccination in hemodialysis patients. Dendritic cells are considered to be the most important antigen presenting cells, but their presence and function in hemodialysis patients is unclear. Granulocyte-monocyte-colony stimulating factor (GM-CSF) has been given successfully to hemodialysis patients to increase the proportion of responders to hepatitis B vaccination. Although GM-CSF acts on both monocytes and dendritic cells, the mechanisms underlying its adjuvant quality are largely unknown.

METHODS

In this study we analyzed monocytes and dendritic cells in the peripheral blood of hemodialysis patient that had responded to a standard hepatitis B vaccination procedure (responders), patients who had not responded (nonresponders), and healthy controls. The nonresponders were given two additional booster vaccines, both preceded by administration of GM-CSF the day before.

RESULTS

After two booster vaccinations with GM-CSF, six out of seven patients developed a protective antibody response to hepatitis B. The memory T-cell response to tetanus toxoid was significantly lower in nonresponders compared to controls. The monocytes of dialysis patients and healthy controls showed a similar expression of relevant cell surface molecules. However, the numbers of circulating dendritic cells were on average 50% reduced compared to healthy controls, with a further reduction after GM-CSF administration. This was accompanied by a decrease of T-cell proliferation in antigen presentation assays. Monocytes showed increased major histocompatibility complex (MHC) class II, CD54, and CD40 expression, while their antigen-presenting capacity remained unchanged.

CONCLUSION

GM-CSF is an effective adjuvant for hepatitis B vaccination in primary nonresponding hemodialysis patients, but paradoxically decreases the antigen presenting capacity of peripheral blood mononuclear cells and the number of circulating dendritic cells.

Targeting dendritic cells for priming cellular immune responses

The cardinal role of dendritic cells (DC) in priming adaptive immunity and in orchestrating immune responses against all classes of pathogens and also against tumors is well established. Their unique potential both to maintain self-tolerance and to initiate protective immune responses against foreign and/or dangerous structures is based on the functional diversity and flexibility of these cells. Tissue DC lining antigenic portals such as mucosal surfaces and the skin are specialized to take up a wide array of compounds including proteins, lipids, carbohydrates, glycoproteins, glycolipids and oligonucleotides, particles carrying such structures and apoptotic or necrotic cells. This process is facilitated by specialized receptors with high endocytic capacity, which provides potential targets for delivering designed molecules. The best route for targeting B- and/or T cell epitopes, however, is still the subject of intense investigation. Immature DC, which reside in various tissues, can be activated by pathogens, stress and inflammation or modified metabolic products, which induce mobilization of cells to draining lymph nodes where they act as highly potent professional antigen presenting cells. This is brought about by the ability to present their accumulated intracellular content for both CD4+ helper (Th) and CD8+ cytotoxic/cytolytic T lymphocytes (Tc/CTL). Engulfed proteins are processed intracellularly and their peptide fragments are transported to the cell surface in the context of major histocompatibility complex encoded class I and II molecules for presentation to Th cells and CTLs, respectively. The T cell priming capacity of DC, however, depends not only on antigen presentation but also on other features of DC. Human monocyte-derived DC provide an excellent tool to study the internalizing, antigen-presenting and T cell-activating functions of DC at their immature and activated differentiation states. These biological activities of DC, however, are highly dependent on their migratory potential from the peripheral non-lymphoid tissues to the lymph nodes, on the expression of adhesion molecules, which support the interaction of DC with T lymphocytes, and the cytokines secreted by DC, which polarize immune responses to Th1-mediated cellular or Th2-mediated antibody responses. These results altogether demonstrate that monocyte-derived DC are useful candidates for in vitro or in vivo targeting of antigens to induce efficient adaptive immune responses against pathogens and also against tumors.

From the Archives of the AFIP

Pulmonary Langerhans cell histiocytosis (PLCH) is an isolated form of Langerhans cell histiocytosis that primarily affects cigarette smokers. PLCH is characterized by peribronchiolar proliferation of Langerhans cell infiltrates that form stellate nodules. The nodular lesions frequently cavitate and form thick- and thin-walled cysts, which are thought to represent enlarged airway lumina. PLCH lesions display temporal microscopic heterogeneity, with progression from dense cellular nodules to apparently cavitary nodules to increasing degrees of fibrosis that may extend along alveolar walls. In advanced cases, fibrotic scars are surrounded by enlarged, distorted air spaces. Affected patients are typically young adults who often present with cough and dyspnea. The characteristic radiographic features of PLCH are bilateral nodular and reticulonodular areas of opacity that predominantly involve the upper and middle lung zones with relative sparing of the lung bases. High-resolution computed tomography (CT) shows nodules and cysts in the same distribution and allows a confident prospective diagnosis of PLCH in the appropriate clinical setting. In typical cases, a predominantly nodular pattern is seen on CT scans in early phases of the disease, whereas a cystic pattern predominates in later phases. The radiologic abnormalities may regress, resolve completely, become stable, or progress to advanced cystic changes. Treatment consists of smoking cessation, but corticosteroid therapy may be useful in selected patients. Chemotherapeutic agents and lung transplantation may be offered to patients with advanced disease. The prognosis of PLCH is variable with frequent regression, stabilization, or recurrence of disease that does not correlate with cessation or continuation of smoking.

Costimulatory molecules and T-cell-B-cell interactions

This article focuses on activating and inhibiting costimulatory signals that are delivered to the T cell from antigen-presenting cells, mediating and modulating T-cell clonal expansion and development of effector functions, as well as costimulatory signals that are delivered by activated T cells to interacting target cells. The coordinated expression and interaction of these molecules regulates responses to foreign antigens and avoidance of response to self-antigens. Knowledge of the structure and function of these costimulatory molecules can be used to manipulate immune function and inhibit autoimmunity and inflammation in the setting of disease.

The COSTIM bioassay: a novel potency test for dendritic cells

The utility of dendritic cells (DCs) in experimental immunotherapy has driven significant advances in the manufacture of these cells. They are increasingly prepared in vitro for use in clinical trials of human disease, particularly cancer. Thus, it has become imperative that, in concert with other quality control measures, a potency test be employed for lot (batch)-release testing of DC products, both in preclinical studies and human clinical trials. The mixed lymphocyte reaction (MLR) assay has served as a 'gold standard' for evaluating the functional ability of antigen presenting cells. Alternatively, some researchers also employ immunophenotyping, a test unrelated to cellular function, as a potency-determining test. We have developed a novel method named the 'COSTIM bioassay', which, as we describe in this paper, is suitable for quality control or lot-release testing. In this method T-cells are stimulated with a sub-optimal amount of anti-CD3 antibody, such that they remain unable to proliferate unless a source of co-stimulation (accessory cells, such as DC) is added to the culture. Thus, the COSTIM bioassay is a functional test that selectively measures co-stimulatory activity, or functional potency. This method takes less than 2 days for completion and assures better quality control than the MLR.

Neuroblastoma and dendritic cell function

Neuroblastoma, the most common extracranial solid tumor of childhood, remains a challenge for clinicians and investigators in pediatric surgical oncology. The absence of effective conventional therapies for most patients with neuroblastoma justifies the application of novel, biology-based, experimental approaches to the treatment of this deadly disease. The observation that some aggressive neuroblastomas, particularly in infants, may spontaneously regress suggested that immune-mediated mechanisms may be important in the biology of this disease. Advances in the understanding of the cognate interactions between T cells, antigen-presenting cells and tumors have demonstrated the sentinel role of dendritic cells (DC), the most potent antigen presenting cells, in initiating the cellular immune response to cancer. Until recently the function of DC in pediatric solid tumors, especially neuroblastoma, had not been extensively studied. This review discusses the role of DC in initiating and coordinating the immune response against cancer, the ability of neuroblastoma to induce DC dysregulation at multiple levels by inhibiting DC maturation and function, and the current vaccine strategies being designed to employ the unique ability of DC to promote neuroblastoma regression.

The soluble form of CD83 dramatically changes the cytoskeleton of dendritic cells

CD83 is the best-known surface marker for mature dendritic cells (DC) and recently we could show that a soluble form of CD83 inhibits DC maturation. In addition, this soluble form inhibits DC-mediated T cell proliferation in vitro and in vivo. Furthermore, several viruses induce CD83 degradation or shedding in infected DC. A soluble form of CD83 was also found in plasma and serum of healthy individuals and interestingly at highly elevated levels in a number of haematological malignancies. Thus, CD83 also has functional implications for the immune response. However, the molecular mechanism is not well defined. Here we describe for the first time that soluble CD83 completely changed the cytoskeleton (analysed using phalloidin-, tubulin- and fascin-specific antibodies) when administered at a concentration of 10 microg/ml to mature DC. The cells rounded off and had only short, truncated, or no veils at all. Furthermore, soluble CD83-treated cells were completely inhibited in their ability to form clusters with T cells, an absolute prerequisite in order to stimulate T cells.

Impaired processing and presentation by MHC class II proteins in human diabetic cells

The biochemical processing of and Ag presentation by MHC class II molecules were examined in B cell lines derived from pairs of identical twins discordant for type 1 diabetes. MHC class II defects detected exclusively in cells derived from the twins with autoimmunity included increased rates of transport to and subsequent turnover at the cell surface, inadequate glycosylation, and a reduced display at the cell surface of antigenic peptides. These defects appeared to be secondary to a decreased abundance of the p35 isoform of the invariant chain (Ii), a human-specific chaperone protein for MHC class II normally generated by use of an alternative translation start site. Stable transfection of diabetic B cell lines with an Ii p35 expression vector corrected the defects in MHC class II processing and peptide presentation. A defect in the expression of Ii p35 may thus result in impairment of Ag presentation by MHC class II molecules and thereby contribute to the development of type 1 diabetes in at-risk genotypes.

TCR triggering on the move: diversity of T-cell interactions with antigen-presenting cells

Polarized T cells are mobile cells optimized for migration, receptor scanning, and signaling. When in contact with antigen-presenting cells (APCs), polarized T cells can develop a spectrum of biophysical interaction modes ranging from adhesive sticking to dynamic crawling. Both static and dynamic contacts support sustained triggering of the T-cell receptor (TCR), leading to signal induction, T blast formation, and proliferation. In dynamic interactions, T cells crawl across the surface of the APC at speeds of 2-6 micro m/min and simultaneously establish an asymmetric tight yet mobile junction plane, representing a dynamic immunological synapse. In dynamic synapses three functional compartments of the polarized T cell are in close contact with the APC surface, i.e. leading edge, cell body and uropod. Through its mobility, the asymmetric junction is topographically suited for receptor scanning and engagement at the leading edge, retrograde receptor movement along the junction, and exit from the uropod. Herein we develop a model on scanning encounters between T cells and APCs that includes the simultaneous engagement of T-cell leading edge and uropod and implicates a serial receptor triggering mode in cell-cell recognition.

Immunological responses are not abnormal in symptomatic Gulf War veterans

The underlying etiology and pathogenesis of Gulf War veterans' illnesses continue to be under intense investigation. Reports have suggested the basis for these illnesses may be an altered immune system, but compelling evidence is lacking. We sought to determine whether in vitro immune responses were abnormal in symptomatic Gulf War veterans relative to matched controls. A randomized case-control study was conducted by blinded comparison of laboratory measures of in vitro immune responses in blood samples obtained from veterans in an outpatient facility of a Veterans Affairs medical center. Symptomatic Gulf War veterans with otherwise undefined illnesses (52 symptomatic subjects), asymptomatic Gulf War veterans (31 asymptomatic controls), and veterans who had applied for disability compensation and had not participated in the Gulf War (21 disability controls) represented the volunteer sample. In vitro cellular and humoral immune responses were measured to detect functional abnormalities in antigen presenting cells (autologous mixed leukocyte reactions and expression of interleukin (IL)-1beta, IL-6, IL-10, and tumor necrosis factor-alpha); T cells (lymphocyte proliferation using the polyclonal T-cell activators phytohemagglutinin and Concanavalin A; primary immune responses in allogeneic mixed leukocyte reactions; secondary immune response using the recall antigens tetanus toxoid, Candida albicans, and anthrax vaccine; and soluble IL-2 receptor expression); type-1 T-helper cells (gamma interferon expression); type-2 T-helper cells (IL-4 and IL-10 expression); and B cells (polyclonal B-cell activator pokeweed mitogen-induced immunoglobulin production). In general, immune response measures did not differ significantly between groups. Heightened responses observed in the disability control group (sporadically greater responses to one mitogen and two antigens) and the Gulf War participation control group (greater recall responses to anthrax vaccine) did not suggest impaired immune cell function in symptomatic veterans when compared with controls. We conclude that in vitro immunological responses are not abnormal in symptomatic Gulf War veterans.

Dendritic cells: a specialized complex system of antigen presenting cells

The dendritic cell (DC) network is a specialized system for presenting antigen to naive or quiescent T cells, and consequently plays a central role in the induction of T cell and B cell immunity in vivo. Despite considerable achievements in the last ten years, in our understanding of how DC induce and regulate immune responses, much remains to be learned about this complex system of cells. The history and current status of DC termed "directors of the immune system orchestra" is reviewed. The present understanding of DC cell biology, function and use, taking into account their complexity is discussed.

Avoiding horror autotoxicus: the importance of dendritic cells in peripheral T cell tolerance

The immune system generally avoids horror autotoxicus or autoimmunity, an attack against the body's own constituents. This avoidance requires that self-reactive T cells be actively silenced or tolerized. We propose that dendritic cells (DCs) play a critical role in establishing tolerance, especially in the periphery, after functioning T cells have been produced in the thymus. In the steady state, meaning in the absence of acute infection and inflammation, DCs are in an immature state and not fully differentiated to carry out their known roles as inducers of immunity. Nevertheless, immature DCs continuously circulate through tissues and into lymphoid organs, capturing self antigens as well as innocuous environmental proteins. Recent experiments have provided direct evidence that antigen-loaded immature DCs silence T cells either by deleting them or by expanding regulatory T cells. This capacity of DCs to induce peripheral tolerance can work in two opposing ways in the context of infection. In acute infection, a beneficial effect should occur. The immune system would overcome the risk of developing autoimmunity and chronic inflammation if, before infection, tolerance were induced to innocuous environmental proteins as well as self antigens captured from dying infected cells. For chronic or persistent pathogens, a second but dire potential could take place. Continuous presentation of a pathogen by immature DCs, HIV-1 for example, may lead to tolerance and active evasion of protective immunity. The function of DCs in defining immunologic self provides a new focus for the study of autoimmunity and chronic immune-based diseases.

Comparison of the accessory activity of murine peritoneal cavity macrophage derived dendritic cells and peritoneal cavity macrophages in a mixed lymphocyte reaction

A detailed comparison of the accessory cell activities was carried out among murine peritoneal cavity macrophages (PEC-Mphi), peritonea] cavity macrophages stimulated with granulocyte-macrophage colony stimulating factor (GM-CSF) plus interleukin 4 (IL-4), the most popular cytokine combination widely used to generate dendritic cells (DC) and peritoneal cavity macrophage-derived DC (PEC-DC) using a two-way mixed lymphocyte reaction (MLR). All the cell types used efficiently induced statistically significant naïve T cell proliferation at all culture time points and responder:stimulator ratios used. However, marked differences were noted in the magnitude of the proliferative responses. These variations may be attributed to the intensity of expression of MHC class II glycoproteins, as well as the actual numbers of MHC class II+ cells.

Signaling lymphocytic activation molecule is expressed on mature CD83+ dendritic cells and is up-regulated by IL-1 beta

Signaling lymphocyte activation molecule (SLAM), a 70-kDa costimulatory molecule that mediates CD28-independent proliferation of T cells and IFN-gamma production, has been identified on human T cells, immature thymocytes, and a subset of B cells. We have found that SLAM is expressed on mature but not immature dendritic cells (DC). However, the SLAM-associated protein, is missing in DC. SLAM surface expression is strongly up-regulated by IL-1beta. Addition of IL-1beta to the DC maturation mixture also increases the stimulatory properties of DC. These findings provide a new marker for DC maturation and help to explain two areas of DC biology. First, SLAM is a receptor for the measles virus, previously shown to infect DC. Second, SLAM could possibly contribute to the enhanced immunostimulatory functions of DC that are observed following the addition of IL-1.

Stimulation of autologous proliferative and cytotoxic T-cell responses by "leukemic dendritic cells" derived from blast cells in acute myeloid leukemia

Effective presentation of tumor antigens is fundamental to strategies aimed at enrolling the immune system in eradication of residual disease after conventional treatments. Myeloid malignancies provide a unique opportunity to derive dendritic cells (DCs), functioning antigen-presenting cells, from the malignant cells themselves. These may then co-express leukemic antigens together with appropriate secondary signals and be used to generate a specific, antileukemic immune response. In this study, blasts from 40 patients with acute myeloid leukemia (AML) were cultured with combinations of granulocyte-macrophage colony-stimulating factor, interleukin 4, and tumor necrosis factor alpha, and development to DCs was assessed. After culture, cells from 24 samples exhibited morphological and immunophenotypic features of DCs, including expression of major histocompatibility complex class II, CD1a, CD83, and CD86, and were potent stimulators in an allogeneic mixed lymphocyte reaction (MLR). Stimulation of autologous T-cell responses was assessed by the proliferative response of autologous T cells to the leukemic DCs and by demonstration of the induction of specific, autologous, antileukemic cytotoxicity. Of 17 samples, 11 were effective stimulators in the autologous MLR, and low, but consistent, autologous, antileukemic cytotoxicity was induced in 8 of 11 cases (mean, 27%; range, 17%-37%). This study indicates that cells with enhanced antigen-presenting ability can be generated from AML blasts, that these cells can effectively prime autologous cytotoxic T cells in vitro, and that they may be used as potential vaccines in the immunotherapy of AML.

Mechanism of NK cell activation induced by coculture with dendritic cells derived from peripheral blood monocytes

Dendritic cells (DCs) have been regarded as one of the effective antigen-presenting cells, but the relationship between DCs and lymphocytes, in particular natural killer (NK) cells, remains unclear. In this study, we evaluated how DCs interact with both lymphocytes and NK cells using a coculture system. The number of lymphocytes increased significantly when cocultured with DCs (1.8-fold increase). In particular, the proliferation of NK cells was prominent. Furthermore, the coculture of DCs with lymphocytes induced a marked increase in IL-12 and IFN-gamma secretion. When contact between the DCs and lymphocytes was prevented, the secretion of both IL-12 and IFN-gamma was markedly reduced. IFN-gamma production was completely blocked by an anti-IL-12 antibody, indicating that IFN-gamma secretion was dependent on IL-12 secretion. The stimulating effect of the DCs on the proliferation of the lymphocytes was partially suppressed by anti-IL-12 antibodies, and was completely attenuated when cellular contact was prevented. Furthermore, the NK cell proliferation induced by coculture with DCs was significantly blocked by the inhibition of the interaction of either CD40-CD40L or CD28-B7 molecule. The coculture with DCs enhanced NK activity by 40%, and this was partially suppressed by anti-IL-12 antibodies and was completely blocked by the inhibition of cell-to-cell contact. These results indicate that the activation of NK cells by DCs is partially mediated by IL-12 secretion, and that direct contact between DCs and NK cells play a major role in this response.

Efficient priming of protein antigen–specific human CD4+ T cells by monocyte-derived dendritic cells

Dendritic cells (DCs) have the unique ability to initiate an immune response in vivo by capturing antigens (Ags) in peripheral tissues and migrating to secondary lymphoid organs, where they sensitize naive CD4+ T cells. To mimic this process in vitro, previous studies have shown that DCs directly isolated from peripheral blood can be used to elicit primary responses to neoantigens (neoAgs). In other studies, when monocyte-derived DCs have been utilized to sensitize total CD4+ T cells in vitro, only secondary proliferation to neoAgs could be elicited. In the present study, the relative abilities of CD40 ligation, protein kinase C activation, and culture in tumor necrosis factor α (TNF-α) to induce functional and phenotypic maturation of human DCs from monocyte precursors were compared. Optimal TNF-α–induced maturation of DCs required a prolonged 4-day culture. It was then found that loading immature DCs with the neoAgs keyhole limpet hemocyanin or human immunodeficiency virus-1 p24 gag prior to TNF-α–induced maturation, rather than after maturation, was crucial to sensitize CD4+ T cells to new Ags. This primary proliferation to neoAgs was initiated from the CD4+ CD45RA+naive T-cell population. Finally, it was found that monocyte-derived DCs acquired the ability to secrete interleukin-12 p70, after contact with Ag-specific T cells. The ability to prime and expand Ag-specific CD4+ T cells ex vivo to neoAgs in serum-free conditions has potential application for cellular vaccination and adoptive immunotherapy.

Efficient priming of protein antigen–specific human CD4+ T cells by monocyte-derived dendritic cells

Dendritic cells (DCs) have the unique ability to initiate an immune response in vivo by capturing antigens (Ags) in peripheral tissues and migrating to secondary lymphoid organs, where they sensitize naive CD4+ T cells. To mimic this process in vitro, previous studies have shown that DCs directly isolated from peripheral blood can be used to elicit primary responses to neoantigens (neoAgs). In other studies, when monocyte-derived DCs have been utilized to sensitize total CD4+ T cells in vitro, only secondary proliferation to neoAgs could be elicited. In the present study, the relative abilities of CD40 ligation, protein kinase C activation, and culture in tumor necrosis factor α (TNF-α) to induce functional and phenotypic maturation of human DCs from monocyte precursors were compared. Optimal TNF-α–induced maturation of DCs required a prolonged 4-day culture. It was then found that loading immature DCs with the neoAgs keyhole limpet hemocyanin or human immunodeficiency virus-1 p24 gag prior to TNF-α–induced maturation, rather than after maturation, was crucial to sensitize CD4+ T cells to new Ags. This primary proliferation to neoAgs was initiated from the CD4+ CD45RA+naive T-cell population. Finally, it was found that monocyte-derived DCs acquired the ability to secrete interleukin-12 p70, after contact with Ag-specific T cells. The ability to prime and expand Ag-specific CD4+ T cells ex vivo to neoAgs in serum-free conditions has potential application for cellular vaccination and adoptive immunotherapy.