Interleukin 1 production during accessory cell-dependent mitogenesis of T lymphocytes

Ion efflux and influenza infection trigger NLRP3 inflammasome signaling in human dendritic cells

The nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome, a multiprotein complex, is an essential intracellular mediator of antiviral immunity. In murine dendritic cells, this complex responds to a wide array of signals, including ion efflux and influenza A virus infection, to activate caspase-1-mediated proteolysis of IL-1β and IL-18 into biologically active cytokines. However, the presence and function of the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome in human dendritic cells, in response to various triggers, including viral infection, has not been defined clearly. Here, we delineate the contribution of the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome to the secretion of IL-1β, IL-18, and IL-1α by human dendritic cells (monocyte-derived and primary conventional dendritic cells). Activation of the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome in human dendritic cells by various synthetic activators resulted in the secretion of bioactive IL-1β, IL-18, and IL-1α and induction of pyroptotic cell death. Cellular IL-1β release depended on potassium efflux and the activity of proteins nucleotide-binding oligomerization domain-like receptor protein 3 and caspase-1. Likewise, influenza A virus infection of dendritic cells resulted in priming and activation of the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome and secretion of IL-1β and IL-18 in an M2- and nucleotide-binding oligomerization domain-like receptor protein 3-dependent manner. The magnitude of priming by influenza A virus varied among different strains and inversely corresponded to type I IFN production. To our knowledge, this is the first report describing the existence and function of the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome in human dendritic cells and the ability of influenza A virus to prime and activate this pathway in human dendritic cells, with important implications for antiviral immunity and pathogenesis.

Blood leukocyte microarrays to diagnose systemic onset juvenile idiopathic arthritis and follow the response to IL-1 blockade

Systemic onset juvenile idiopathic arthritis (SoJIA) represents up to 20% of juvenile idiopathic arthritis. We recently reported that interleukin (IL) 1 is an important mediator of this disease and that IL-1 blockade induces clinical remission. However, lack of specificity of the initial systemic manifestations leads to delays in diagnosis and initiation of therapy. To develop a specific diagnostic test, we analyzed leukocyte gene expression profiles of 44 pediatric SoJIA patients, 94 pediatric patients with acute viral and bacterial infections, 38 pediatric patients with systemic lupus erythematosus (SLE), 6 patients with PAPA syndrome, and 39 healthy children. Statistical group comparison and class prediction identified genes differentially expressed in SoJIA patients compared with healthy children. These genes, however, were also changed in patients with acute infections and SLE. An analysis of significance across all diagnostic groups identified 88 SoJIA-specific genes, 12 of which accurately classified an independent set of SoJIA patients with systemic disease. Transcripts that changed significantly in patients undergoing IL-1 blockade were also identified. Thus, leukocyte transcriptional signatures can be used to distinguish SoJIA from other febrile illnesses and to assess response to therapy. Availability of early diagnostic markers may allow prompt initiation of therapy and prevention of disabilities.

Interleukin-1 blockade does not prevent acute graft-versus-host disease: results of a randomized, double-blind, placebo-controlled trial of interleukin-1 receptor antagonist in allogeneic bone marrow transplantation

Acute graft-versus-host disease (GVHD) is thought to derive from direct T-cell injury of target tissues through perforin/granzyme, Fas/FasL interactions, and the effects of inflammatory cytokines. Animal models and some clinical trials support the notion that inhibition of inflammatory mediators such as interleukin-1 (IL-1), tumor necrosis factor alpha, and interferon gamma may ameliorate or prevent GVHD. We hypothesized that blockade of IL-1 during the period of initial T-cell activation would reduce the risk of severe GVHD. We tested this hypothesis in a double-blind, placebo-controlled randomized trial of recombinant human IL-1 receptor antagonist (IL-1Ra) in 186 patients undergoing allogeneic stem cell transplantation. Randomization was stratified by degree of histocompatibility and stem cell source. All patients were conditioned with cyclophosphamide and total body irradiation. GVHD prevention consisted of cyclosporine and methotrexate in all patients. Recombinant human IL-1Ra or saline placebo was given from day -4 to day +10. Randomization was stratified according to GVHD risk. The 2 groups were well-matched for pretreatment characteristics. Moderate to severe GVHD (grades B-D) developed in 57 (61%) of 94 patients receiving IL-1Ra and in 51 (59%) of 86 patients on placebo (P =.88). There was no difference in hematologic recovery, transplantation-related toxicity, event-free survival, or overall survival. We conclude that blockade of IL-1 using IL-1Ra during conditioning and 10 days immediately after transplantation is not sufficient to reduce GVHD or toxicity or to improve survival.

Secretion of bioactive interleukin-1β by dendritic cells is modulated by interaction with antigen specific T cells

The role of interleukin-1β (IL-1β) as a regulator of the immune response, although extensively investigated, is still debated. We then studied the expression of IL-1β by human dendritic cells (DCs), the professional antigen presenting cells, and its modulation during immune reactions in vitro. Our results show that, on maturation or tetanus toxoid presentation to specific CD4+ CD40L+T lymphocytes, DCs begin to accumulate IL-1β precursor (pro–IL-1β) but do not secrete bioactive IL-1β. In contrast, interaction with alloreactive T cells results in both stimulation of pro–IL-1β synthesis and secretion of processed isoforms of the cytokine, that display biologic activity. Both CD4+ and CD8+ subsets of allospecific T lymphocytes are required: CD4+ T cells drive the synthesis of pro–IL-1β through CD40 engagement but have no effects on pro–IL-1β processing; CD8+ T cells, unable to induce synthesis of pro–IL-1β per se, are responsible for the generation of mature IL-1β by pro–IL-1β–producing DCs. Interleukin-1β–converting enzyme (ICE) inhibitors do not prevent the recovery of IL-1β bioactivity after allorecognition, indicating that allospecific CD8+ T cells may induce the release of bioactive IL-1β via mechanism(s) other than ICE activation. Altogether, these findings suggest that CD4+ and CD8+ T-lymphocyte subsets have distinct roles in the induction of IL-1β secretion by DCs and support the hypothesis that IL-1β plays a role in cell-mediated immune responses.

Secretion of bioactive interleukin-1β by dendritic cells is modulated by interaction with antigen specific T cells

The role of interleukin-1β (IL-1β) as a regulator of the immune response, although extensively investigated, is still debated. We then studied the expression of IL-1β by human dendritic cells (DCs), the professional antigen presenting cells, and its modulation during immune reactions in vitro. Our results show that, on maturation or tetanus toxoid presentation to specific CD4+ CD40L+T lymphocytes, DCs begin to accumulate IL-1β precursor (pro–IL-1β) but do not secrete bioactive IL-1β. In contrast, interaction with alloreactive T cells results in both stimulation of pro–IL-1β synthesis and secretion of processed isoforms of the cytokine, that display biologic activity. Both CD4+ and CD8+ subsets of allospecific T lymphocytes are required: CD4+ T cells drive the synthesis of pro–IL-1β through CD40 engagement but have no effects on pro–IL-1β processing; CD8+ T cells, unable to induce synthesis of pro–IL-1β per se, are responsible for the generation of mature IL-1β by pro–IL-1β–producing DCs. Interleukin-1β–converting enzyme (ICE) inhibitors do not prevent the recovery of IL-1β bioactivity after allorecognition, indicating that allospecific CD8+ T cells may induce the release of bioactive IL-1β via mechanism(s) other than ICE activation. Altogether, these findings suggest that CD4+ and CD8+ T-lymphocyte subsets have distinct roles in the induction of IL-1β secretion by DCs and support the hypothesis that IL-1β plays a role in cell-mediated immune responses.

Interleukin-1 receptor antagonist suppresses contact hypersensitivity

Interleukin-1 receptor antagonist (IL-1ra), a naturally occurring inhibitor of interleukin-1 (IL-1), blocks IL-1 binding to its receptors but has no agonistic activity. IL-1 is thought to play an important role in contact hypersensitivity (CHS), although the effects of exogenously administered IL-1 in CHS have been somewhat controversial. To clarify the role of IL-1 in CHS, we studied the effect of IL-1 receptor blockade using exogenous IL-1ra and evaluated these effects on CHS. We examined the in vivo effects of local administration of recombinant human IL-1ra in the murine CHS model. Local injection of IL-1ra to sensitized BALB/c mice just before challenge with dinitrofluorobenzene resulted in a significant reduction in the intensity of CHS responses, assessed by ear swelling. A dose-response study revealed that maximal inhibition of ear swelling (36% to 43%) was observed after intradermal injection of IL-1ra at doses of 10 to 100 micrograms/ear. This reduction in ear swelling in IL-1ra-injected ears consisted of less inflammatory cell infiltration and decreased edema in the dermis compared with controls. Suppression of CHS was observed when IL-1ra was applied in the 24-h interval preceding challenge with dinitrofluorobenzene, whereas no suppressive effect was observed when IL-1ra was applied 48 h before or after the challenge. Local administration of IL-1ra to naive mice 5 h before sensitization also suppressed CHS responses. However, IL-1ra injection did not suppress phenol-induced inflammation. These results suggest that IL-1ra is an effective inhibitor of both the sensitization and elicitation phases of CHS expression in mice, thus emphasizing the role of IL-1 as an immunologic potentiator of responses associated with CHS.

Post-traumatic activation of draining lymph node cells. II. Proliferative and phenotypic characteristics

Proliferative and phenotypic characteristics of cells in regional lymph nodes that drain burn injury were examined in rats on day 3 postburn, i.e. at the time of maximal spontaneous proliferation and of interleukin-2 and accessory cytokine (IL-1 and IL-6) production. The importance of IL-1 in spontaneous proliferation of draining lymph node cells was demonstrated by stimulation of IL-2-driven proliferation by recombinant IL-1 in vitro and by susceptibility of unstimulated proliferation to anti-IL-1 antibodies, while requirements for IL-6 in draining lymph node cell proliferation were less pronounced. Cell surface phenotyping revealed a slightly increased percentage of CD25+ cells in the blast cell population of freshly isolated draining lymph node cells after injury, which increased further during cultivation. Enrichment in CD8+ cells on day 3 following burn injury was demonstrated, while no changes in total cell population and CD4+ cells was noted. This was however preceded by pronounced percentual decrease of total T cells and CD4+ cells and by increases of B cells and MHC class II+ cells on day 1 postburn. Inhibition of draining lymph node cell proliferation by anti-MHC class II antibodies suggested that this proliferation was class II MHC dependent. The contribution of cell proliferation and/or cell influx to day 3 postburn draining lymph node cell activity is discussed.

Influenza virus-infected dendritic cells stimulate strong proliferative and cytolytic responses from human CD8+ T cells

Antigen-specific, CD8+, cytolytic T lymphocytes (CTLs) could potentially provide resistance to several infectious and malignant diseases. However, the cellular requirements for the generation of specific CTLs in human lymphocyte cultures are not well defined, and repetitive stimulation with antigen is often required. We find that strong CD8+ CTL responses to influenza virus can be generated from freshly isolated blood T cells, as long as dendritic cells are used as antigen presenting cells (APCs). Small numbers of dendritic cells (APC:T cell ratio of 1:50-1:100) induce these CTL responses from most donors in 7 d of culture, but monocytes are weak or inactive. Whereas both dendritic cells and monocytes are infected with influenza virus, the former serve as effective APCs for the induction of CD8+ T cells while the latter act as targets for the CTLs that are induced. The strong CD8+ response to influenza virus-infected dendritic cells is accompanied by extensive proliferation of the CD8+ T cells, but the response can develop in the apparent absence of CD4+ helpers or exogenous lymphokines. CD4+ influenza virus-specific CTLs can also be induced by dendritic cells, but the cultures initially must be depleted of CD8+ cells. These findings should make it possible to use dendritic cells to generate human, antigen-specific, CD8+ CTLs to other targets. The results illustrate the principle that efficient T cell-mediated responses develop in two stages: an afferent limb in which dendritic cells are specialized APCs and an efferent limb in which the primed T cells carry out an immune response to many types of presenting cells.

CD28-induced costimulation of T helper type 2 cells mediated by induction of responsiveness to interleukin 4

Type 1 and type 2 cloned T helper (Th) cells are believed to require different antigen-presenting cell (APC)-derived costimuli for proliferation. In the case of Th1-cloned T cells, CD28 signaling costimulates production of autocrine interleukin 2 (IL-2). Th2 cells produce their autocrine growth factor, IL-4, without costimulation, but require APC-derived costimuli, or IL-1, to respond to IL-4. Here we demonstrate that engagement of CD28 on Th2 cells with anti-CD28 antibody or with APC-associated B7 costimulates Th2 responsiveness to IL-4 but does not affect IL-4 or IL-2 production by Th2 cells. Costimulation of Th2 cells via CD28 appears to involve the induction of IL-1 production by Th2 cells, which acts in an autocrine fashion to induce IL-4 responsiveness. These results suggest that CD28-induced costimulation plays an important role in responses mediated by both types of Th cells.

Dendritic cells freshly isolated from human blood express CD4 and mature into typical immunostimulatory dendritic cells after culture in monocyte-conditioned medium

A procedure has been developed to isolate dendritic cells to a high degree of purity from fresh blood. Prior enrichment methods have relied upon an initial 1-2-d culture period. Purified fresh isolates lack the characteristic morphology, phenotype, and immunostimulatory function of dendritic cells. The purified cells have the appearance of medium sized lymphocytes and express substantial levels of CD4, but lack the T cell molecules CD3, CD8, and T cell receptor. When placed in culture, the cells mature in a manner resembling the previously described, cytokine-dependent maturation of epidermal dendritic cells (Langerhans cells). The cells enlarge and exhibit many cell processes, express much higher levels of major histocompatibility complex class II and a panel of accessory molecules for T cell activation, and become potent stimulators of the mixed leukocyte reaction. Among the many changes during this maturation process are a fall in CD4 and the appearance of high levels of B7/BB1, the costimulator for enhanced interleukin 2 production in T cells. These changes are not associated with cell proliferation, but are dependent upon the addition of monocyte-conditioned medium. We suggest that the freshly isolated CD4-positive blood dendritic cells are recent migrants from the bone marrow, and that subsequent maturation of the lineage occurs in tissues in situ upon appropriate exposure to cytokines.

Interstitial dendritic cells of the rat heart. Quantitative and ultrastructural changes in experimental myocardial infarction

BACKGROUND

This study was undertaken to investigate the qualitative and quantitative changes that interstitial dendritic cells (IDC) of the heart undergo during the time course of experimental myocardial infarction.

METHODS AND RESULTS

Left coronary arterial ligations were performed in 43 rats that were killed 2, 4, 7, 14, and 21 days after surgery. Thirteen unoperated and 39 sham-operated rats were used as controls. Frozen sections were stained with monoclonal antibodies (OX 6 and W3/25) to identify and count IDC by light microscopy. Immunoelectron microscopy was also used to identify IDC. The number of IDC per mm2 of tissue section was calculated for all hearts. In hearts with myocardial infarction, IDC were counted in three areas: the center of the myocardial infarction, the border zone, and the noninfarcted left ventricle. In OX 6 antibody-stained preparations, the number of IDC per mm2 was 82 +/- 10 in the left ventricle of unoperated rats. Hearts with myocardial infarction showed marked increases in the numbers of IDC per mm2 in the border zone (796 +/- 79 at 7 days and 528 +/- 98 at 14 days). In the border zone, IDC often were associated with small clusters of T-helper lymphocytes, which reacted with W3/25 antibody (the rat homologue of human CD4). The center of the myocardial infarction showed an increase in IDC only on day 7 (120 +/- 18). By 21 days, IDC in the border zone were only slightly increased (159 +/- 15).

CONCLUSIONS

These findings suggest that IDC migrate to the myocardial infarction border zone. They participate in the activation of lymphocytes and in the initiation of immune responses and decrease in number as inflammation subsides and scarring develops.

Synergistic enhancement of T cell responses and interleukin-1 receptor expression by interleukin-1 and heparin or dextran sulfate

Heparin markedly enhances generation of cytotoxic T lymphocytes against allogeneic cells and histocompatible tumors. In this study, we demonstrated a marked synergism between heparin and low concentrations of recombinant IL-1-alpha and IL-1-beta in enhancement of cytotoxic T cell responses in mice. Low molecular weight (8000 Da) dextran sulfate also enhanced the T cell responses and synergized with IL-1, whereas, de-N-sulfated heparin was devoid of both of these activities. The synergistic effect was selective for IL-1, because there was no synergism between heparin or dextran sulfate and other cytokines (tumor necrosis factor-alpha, IL-4, and, as shown previously, IL-2). Heparin did not increase the production of IL-1 (and IL-2, as shown before). Heparin did not bind to IL-1, despite significant amino acid homology between IL-1 and heparin-binding endothelial cell growth factors. Heparin enhanced the growth-promoting effect of IL-1 on the IL-1-dependent helper T cell clone, D10.G4.1, and enhanced IL-1 receptor expression on these cells. These data indicate that heparin acts directly on the T cells and enhances their responsiveness to IL-1 by up-regulating IL-1 receptor expression.

A fail-safe mechanism for maintaining self-tolerance

Using cytotoxic T lymphocyte (CTL) responses to the class I histocompatibility antigen Qa1 and to the minor histocompatibility antigen H-Y, we show that the immune system maintains a peripheral screening process that is able to tolerize a wide variety of potentially autoimmune CTL. The critical factor is the presence or absence of specific T helper cells. If T help is available, CTL precursors that recognize antigen are activated. In the absence of help, they are tolerized. Thus, T helper cells are guardians of peripheral tolerance in CTL.

Accessory function of endothelial cells in anti-CD3-induced T-cell proliferation: synergism with monocytes

Monoclonal antibodies to CD3 can induce proliferation of resting T cells. In vitro this effect is dependent on the presence of monocytes. They serve as accessory cells providing a co-stimulatory signal after cross-linking of the antibody-coated TcR/CD3 complex by the Fc receptor on the monocytes. We have studied whether endothelial cells can replace monocytes with regard to this function. Highly purified T-cell preparations were cultured in the presence of anti-CD3 antibody, purified monocytes, and human umbilical vein endothelial cells. Anti-CD3 and endothelial cells alone were unable to support T-cell proliferation, due to lack of FcR expression. Addition, however, of as few as 1000 FcR+ monocytes (0.8% of the number of T cells present) to a coculture of T cells and endothelial cells (EC) in the presence of soluble anti-CD3 resulted in a strong proliferation of T cells. When anti-CD3 was presented in an immobilized form (coated to the culture well or to Sepharose beads), or when phytohaemagglutinin was added to the culture as a cross-linking agent, EC could support T-cell proliferation in the absence of any monocytes. We conclude that EC by themselves cannot support the proliferation of pure T cells induced by soluble anti-CD3, but are potent generators of the co-stimulatory signal(s). They provide a suitable starting material to further define this co-stimulatory activity.

FcR+ and FcR- monocytes differentially secrete monokines during pokeweed mitogen-induced T-cell-monocyte interactions

Monocyte subpopulations which differ in the expression of Fc receptor for human IgG (FcRI) differentially regulate the T-cell-dependent, pokeweed mitogen (PWM)-induced, polyclonal B-cell response. We, thus, studied the cytokine production in human peripheral blood monocyte and T-lymphocyte cultures activated with this lectin. Monocytes or their FcR+ and FcR- subpopulations stimulated with PWM were cultured with or without T lymphocytes or their CD4+ and CD8+ subsets. Both monocyte subpopulations cultured alone produced similar amounts of tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), but FcR- monocytes showed significantly enhanced ability to secrete interleukin-1 (IL-1). T cells, especially CD4+, added to monocyte cultures enhanced IL-1 production. This enhancement was presumably due to interferon-gamma (IFN-gamma) release by T lymphocytes, since this lymphokine enhanced IL-1 secretion when added to PWM-stimulated cultures of monocytes. Addition of monocytes, in particular the FcR+ subpopulation, greatly enhanced production of IFN-gamma by T lymphocytes. Although both T-cell subsets produced IFN-gamma, the CD4+ cells were more efficient. These results indicate that in PWM-stimulated cultures subpopulations of monocytes differ in secretion of cytokines, which might explain their differential effect on T-cell-dependent immune responses in vitro.

Signals arising from antigen-presenting cells

It has been customary to consider that antigen-presenting cells provide, in addition to the presented antigen, a second or co-stimulatory signal that leads to T-cell growth and effector function. The recent literature indicates that this two-signal notion oversimplifies the function of antigen-presenting cells. Instead it is useful to consider four groups of events: the formation of peptide-MHC complexes, the role of soluble cytokines, the action of antigen-presenting cell-T cell molecular couples distinct from the receptor for peptide MHC, and the function of antigen-presenting cells in situ.

Production of interleukin-1 by draining lymph node cells during the induction phase of contact sensitization in mice

Biologically active interleukin-1 (IL-1) has been detected in supernatants of draining lymph node cells isolated from contact-sensitized mice. Induction of IL-1 was dependent upon the concentration of sensitizer applied and occurred within 2 hr of exposure. The IL-1 activity could not be attributed to other interleukins and was neutralized by a specific antiserum. Reduced concentrations of IL-1 were produced by cells isolated from the draining nodes of mice that had been pre-exposed to the sensitizer. Since IL-1 has the potential to influence several aspects of lymphocyte activation, the production of significant concentrations of biologically active IL-1 by draining lymph node cells indicates that it is likely to play an important role in the afferent phase of contact sensitization.

Lymphoid dendritic accessory cells of the rat

The expression of MHC class II antigens on potential APC is a crucial step in T-lymphocyte activation and the initiation of an immune response. The studies which are presented here were initiated to characterize the critical APC present in physiologically normal, untreated rats. Such a cell should constitutively express these antigens at high density and therefore provide the apparatus necessary to provoke both primary and secondary immune responses at any time. DAC were found to fulfill these criteria. In the absence of specific surface markers of rat DAC, the results are based on the strict combination of morphological appearance and functional activity. However, the high expression of MHC class II antigens may be regarded as semispecific markers for DAC which are distributed at strategic positions in many lymphoid and nonlymphoid tissues (Hart & Fabre 1981, Steiniger et al. 1984). The relatively low number of these cells observed in tissue sections and in in vitro isolates (0.1% of all cells) may explain their high activity as APC. This would facilitate the presentation of antigen in vivo to a sufficient number of competent T lymphocytes. DAC differentiate from a bone marrow progenitor cell pool preferentially under the influence of spleen cell-derived activities. Although the exact lineage has not yet been determined it may be fair to speculate that DAC form a new cell lineage probably related to interdigitating cells but not to macrophages which differentiate from bone marrow-derived precursors under the influence of colony-stimulating activities. However, the cooperation between DAC plus macrophages may provide the stage for T-lymphocyte activation and T-T collaboration (Mitchison 1990). There are still many open questions concerning the general role of DAC in vivo and in vitro. To further characterize rat DAC, their tissue distribution, role in the immune response and possible influence on intrathymic lymphopoiesis, with respect to T-lymphocyte subpopulations and the selection of the T-lymphocyte antigen-receptor repertoire, a panel of DAC-specific monoclonal antibodies must be generated in the future. Such antibodies will also be useful to study the mechanism by which DAC activate T lymphocytes.

Dendritic cells pulsed with protein antigens in vitro can prime antigen-specific, MHC-restricted T cells in situ

T cells recognize peptides that are bound to MHC molecules on the surface of different types of antigen-presenting cells (APC). Antigen presentation most often is studied using T cells that have undergone priming in situ, or cell lines that have been chronically stimulated in vitro. The use of primed cells provides sufficient numbers of antigen-reactive lymphocytes for experimental study. A more complete understanding of immunogenicity, however, requires that one develop systems for studying the onset of a T cell response from unprimed lymphocytes, especially in situ. Here it is shown that mouse T cells can be reliably primed in situ using dendritic cells as APC. The dendritic cells were isolated from spleen, pulsed with protein antigens, and then administered to naive mice. Antigen-responsive T cells developed in the draining lymphoid tissue, and these T cells only recognized protein when presented on cells bearing the same MHC products as the original priming dendritic cells. In contrast, little or no priming was seen if antigen-pulsed spleen cells or peritoneal cells were injected. Since very small amounts of the foreign protein were visualized within endocytic vacuoles of antigen-pulsed dendritic cells, it is suggested that dendritic cells have a small but relevant vacuolar system for presenting antigens over a several day period in situ.

Dissociation between allogeneic T cell stimulation and interleukin-1 or tumor necrosis factor production by human lung dendritic cells

A small portion of human lung mononuclear cells are very potent stimulators of allogeneic resting T cells. Although several-fold more effective than phagocytic alveolar macrophages (AM) and blood monocytes (Mo), they do not produce more of the lymphocyte co-stimulators interleukin-1-alpha (IL-1 alpha), interleukin-1-beta (IL-1 beta), or tumor necrosis factor-alpha (TNF-alpha) than did Mo. Blocking antibodies against IL-1 alpha, IL-1 beta, TNF-alpha, and IL-6 did not reduce T cell proliferation. These potent antigen-presenting cells (APC) are loosely adherent and do not have phagocytic inclusions. Most of them have the marker RFD1 of dendritic cells (DC) rarely present on Mo or AM and have a strong tendency to form clusters with T cells like murine DC. Thus, we demonstrate an example in the human system of a dissociation between T cell activation and IL-1 or TNF-alpha production by DC or Mo, implying a major role for other "co-stimulating signals" by lung APC with dendritic features. The presence of different APC with various co-stimulating signals may be of importance for T cell subsets modulation.

Mechanisms of dendritic cell function

There is now considerable evidence, from in vivo and in vitro studies, supporting the claim that dendritic cells are the principal accessory cells of the vertebrate immune system. Until recently, however, the biology of the dendritic cell accessory mechanism has remained obscure. Here, Philip King and David Katz review recent findings that have clarified several aspects of this mechanism, providing a possible basis for the potent T-cell stimulating capacity of the dendritic cell, and yielding clues to the ontogenetic relationships of these cells and to their role in immunopathology.

Production of interleukin 1 alpha by a trichilemmoma cell line

In order to obtain a good source of human epidermal cell derived thymocyte activating factor (ETAF) for biological study, several cell lines of epidermal origin were cultured. One of the trichilemmoma cell lines, KTL-1, was found to produce ETAF satisfactorily in its culture supernatant. The culture supernatant was collected and analyzed to determine the nature of the ETAF activity. The ETAF activity was completely inhibited by anti-IL 1 alpha antibody, but not by anti-IL 1 beta antibody. Messenger RNA expression by KTL-1 cells was analyzed by using cDNA of IL 1 alpha as a probe. Messenger RNA was not detected in KTL-1 cells by either dot blot analysis or northern blot analysis. However, it was expressed weakly in the cytoplasm by in situ hybridization technique. Messenger RNA expression was easily detected in KTL-1 cells stimulated by lipopolysaccharide (LPS). Messenger RNA expression reached a peak at 3 hours after stimulation of LPS. A trichilemmoma cell line, KTL-1, can be a good source of human ETAF for biological study.

Human peripheral blood-derived dendritic cells do not produce interleukin 1 alpha, interleukin 1 beta, or interleukin 6

Little is known about the non-antigen-specific signals delivered to T cells by dendritic cells (DC). Because several monocyte-derived factors like interleukins 1 alpha, 1 beta, and 6 (IL-1 alpha, IL-1 beta, and IL-6) enhance the T-cell proliferative responses, we studied the production of the above-mentioned cytokines by DC separated from human peripheral blood. The intracellular expression of the proteins (IL-1 alpha and IL-6) was studied at a single-cell level using an immunolabelling technique. The supernatants and cell lysates were studied with ELISA (IL-1 alpha and IL-1 beta). Northern blotting analysis was used to quantitate the mRNA levels. Several approaches were taken to stimulate the production of IL-1 alpha, IL-1 beta, and IL-6 by DC. These included the incubation of the DC in the presence of either LPS, rIL-1, or monoclonal anti-HLA-DR antibody, or the stimulation of cells with resting allogeneic T cells. None of the stimuli was able to induce the production of IL-1 alpha, IL-1 beta, or IL-6 by DC, whereas LPS-stimulated monocytes were strong producers of these mentioned cytokines and expressed the respective mRNA. Thus we concluded that IL-1 alpha, IL-1 beta, and IL-6 are primarily monocyte-derived factors and that these factors are not needed or produced during the activation of resting T cells by DC.

Dendritic cell production of cytokines and responses to cytokines

Dendritic cells (DC) are a family of bone marrow-derived MHC class II expressing cells which occur in small numbers in most lymphoid and nonlymphoid tissues. They represent a distinct lineage of leukocytes which can be found in two distinct maturational stages: immature dendritic cells are exemplified by the Langerhans cells in the epidermis, and are considered to be precursors to the mature dendritic cells in the lymphoid organs. These maturational stages can be distinguished by phenotypic and functional characteristics. Immature dendritic cells are weak stimulators of resting T lymphocytes but are excellent in processing soluble protein antigens for presentation to T cell clones. Mature dendritic cells show exactly reciprocal features. In this review the relatively few available data on cytokine production by DC and responses of DC to cytokines are collected. Our goal is to consider the role of cytokines in DC function including the transition from immature to mature stages.

Interstitial dendritic cells

Interstitial dendritic cells (IDC) were first identified in the interstitium of non-lymphoid organs as leucocytes which stained intensely with anti-MHC class II antibodies. These cells have been identified in several species including man, and can be distinguished from tissue macrophages by their immunological phenotype and cytochemical and functional characteristics. IDC appear to be closely related to lymphoid dendritic cells (DC), and have the capacity to bind antigen and stimulate T lymphocyte responses. It seems probable that they represent a stage of nonlymphoid dendritic cell differentiation necessary for antigen surveillance, similar to the Langerhans cell of the skin. Exposure to antigen appears to induce migration of these cells into adjacent lymphatics and subsequent localization in the interfollicular areas of lymph node, where the DC present processed antigen to activate a primary T cell response. The IDC has been identified as the passenger leucocyte within organ allografts which contributes substantially to graft immunogenicity, so that eradication of donor organ IDC improves organ graft survival.

Dendritic cells as antigen presenting cells in vivo

The biology of antigen presenting cells (APC) traditionally is studied in tissue culture systems using T cells that have been expanded beforehand by stimulation with antigen. Here we consider the distinctive roles of dendritic cells for sensitizing or priming T cells both in vitro and in vivo. Several functions of dendritic cells have been identified in tissue culture that are pertinent to T cell sensitization. These include the ability to a) capture and retain foreign antigens in an immunogenic form, b) bind antigen-specific resting lymphocytes, and c) activate T cells to produce lymphokines and undergo long term clonal growth. Dendritic cells have several properties in vivo that also would contribute to APC function. These are a) their widespread tissue distribution permitting access to antigens in most organs, b) the capacity to home via the blood stream and afferent lymph to the T-dependent areas of spleen and lymph node, and c) the ability to capture antigen in antigen-pulsed animals. Dendritic cells bearing antigen have been administered in situ to initiate responses like contact sensitivity, graft rejection, and antibody formation. A most striking recent example is that, when dendritic cells are pulsed with protein antigens in vitro and administered to immunologically naive mice, there is direct priming of antigen-specific T cells that are restricted to the MHC of the injected APC.

Dendritic cells in human blood and synovial exudates

Dendritic cells from human blood and synovial exudates are distinct from other leukocytes and are homogeneous by several criteria. Morphologically, their most prominent feature is numerous veils. Phenotypically, dendritic cells lack the surface antigens that identify monocytes, T cells, B cells, and NK cells. Human dendritic cells strongly express class I and class II MHC products, and have a distinct array of integrin and adhesin molecules. In many systems, dendritic cells are potent stimulators of T cell function. In the allogeneic mixed leukocyte reaction, for example, dendritic cells are 30-100 times more efficient than other cells in presenting transplantation antigens, for the induction of DNA synthesis, cytokine release, and generation of cytotoxic T cells. In addition, dendritic cells can induce the long-term clonal growth of T lymphocytes. Although dendritic cells are a minor subpopulation in human blood, new isolation protocols are available that permit efficient isolation and enrichment to > 90%.

An antigen-independent contact mechanism as an early step in T cell-proliferative responses to dendritic cells

Dendritic cells bearing antigen efficiently aggregate and stimulate antigen-specific T cells. We describe an experimental model in which an initial, apparently antigen-independent binding step is followed by ligation of the TCR. The model is the polyclonal response to mAb to the CD3 portion of the TCR complex. Epidermal and thymic dendritic cells utilize low levels of Fc receptors to present the anti-CD3 mAb and induce mitogenesis. Within 3 h of coculture, most of the dendritic cells have formed clusters with the resting T lymphocytes, and these clusters are the site for subsequent DNA synthesis and cell growth. However, the binding of dendritic cells to T cells proceeds as efficiently in the absence of anti-CD3 as in its presence, and anti-FcR mAb does not block. CD3 and Fc receptors are essential for the subsequent mitogenesis response in dendritic-T cell clusters. Because an exogenous ligand for the TCR does not seem to be required for the extensive polyclonal clustering of resting lymphocytes to dendritic cells, we suggest that an antigen-independent mechanism mediates the initial interaction. This clustering seems essential for T cell growth since we do not detect, in two-chamber experiments, soluble lymphocyte-activating factors that originate from dendritic-T cell aggregates and that activate anti-CD3-coated T cells.