Involvement of interleukin-18 (IL-18) in mixed lymphocyte reactions (MLR)

Isolation of Rat Lung Mast Cells for Purposes of One-Week Cultivation Using Novel Percoll Variant Percoll PLUS

Prolonged cultivation of separated rat lung mast cells (LMC) in vitro is necessary to better investigate a possible role of LMC in different stages of tissue remodeling induced by hypoxia. Rat lung mast cells (LMC) were separated using a protocol including an improved proteolytic extraction and two subsequent density gradient separations on Ficoll-Paque PLUS and a new generation of Percoll, i.e. Percoll PLUS. Instead of usual isotonic stock Percoll solution, an alternative “asymptotically isotonic” stock solution was more successful in our density separation of LMC on Percoll PLUS. Separated cells were cultivated for six days in media including stem cell factor, interleukins IL-3 and IL-6, and one of two alternative mixtures of antibiotics. These cultivations were performed without any contamination and with only rare changes in cell size and morphology. Model co-cultivation of two allogenic fractions of LMC often caused considerable rapid changes in cell morphology and size. In contrast to these observations no or rare morphological changes were found after cultivation under hypoxic conditions. In conclusions, we modified separation on Percoll PLUS to be widely used, altered LMC separation with respect to purposes of long-lasting cultivation and observed some model morphological changes of LMC.

Incorporation of CD40 ligand into the envelope of pseudotyped single-cycle Simian immunodeficiency viruses enhances immunogenicity

A vaccine for the prevention of human immunodeficiency virus (HIV) infection is desperately needed to control the AIDS pandemic. To address this problem, we developed vesicular stomatitis virus glycoprotein-pseudotyped replication-defective simian immunodeficiency viruses (dSIVs) as an AIDS vaccine strategy. The dSIVs retain characteristics of a live attenuated virus without the drawbacks of potential virulence caused by replicating virus. To improve vaccine immunogenicity, we incorporated CD40 ligand (CD40L) into the dSIV envelope. CD40L is one of the most potent stimuli for dendritic cell (DC) maturation and activation. Binding of CD40L to its receptor upregulates expression of major histocompatibility complex class I, class II, and costimulatory molecules on DCs and increases production of proinflammatory cytokines and chemokines, especially interleukin 12 (IL-12). This cytokine polarizes CD4(+) T cells to Th1-type immune responses. DC activation and mixed lymphocyte reaction (MLR) studies were performed to evaluate the immunogenicity of CD40L-dSIV in vitro. Expression levels of CD80, CD86, HLA-DR, and CD54 on DCs transduced with the dSIV incorporating CD40L (CD40L-dSIV) were significantly higher than on those transduced with dSIV. Moreover, CD40L-dSIV-transduced DCs expressed up to 10-fold more IL-12 than dSIV-transduced DCs. CD40L-dSIV-transduced DCs enhanced proliferation and gamma interferon secretion by naive T cells in an MLR. In addition, CD40L-dSIV-immunized mice exhibited stronger humoral and cell-mediated immune responses than dSIV-vaccinated animals. The results show that incorporating CD40L into the dSIV envelope significantly enhances immunogenicity. As a result, CD40L-dSIVs can be strong candidates for development of a safe and highly immunogenic AIDS vaccine.

IL-23 is increased in dendritic cells in multiple sclerosis and down-regulation of IL-23 by antisense oligos increases dendritic cell IL-10 production

IL-23 is a heterodimeric cytokine comprising a p19 subunit associated with the IL-12/23p40 subunit. Like IL-12, IL-23 is expressed predominantly by activated dendritic cells (DCs) and phagocytic cells, and both cytokines induce IFN-gamma secretion by T cells. The induction of experimental autoimmune encephalitis, the animal model of multiple sclerosis (MS), occurs in mice lacking IL-12, but not in mice with targeted disruption of IL-23 or both IL-12 and IL-23. Thus, IL-23 expression in DCs may play an important role in the pathogenesis of human autoimmune diseases such as MS. We quantified the expression of IL-23 in monocyte-derived DCs in MS patients and healthy donors and found that DCs from MS patients secrete elevated amounts of IL-23 and express increased levels of IL-23p19 mRNA. Consistent with this abnormality, we found increased IL-17 production by T cells from MS patients. We then transfected monocyte-derived DCs from healthy donors with antisense oligonucleotides specific for the IL-23p19 and IL-12p35 genes and found potent suppression of gene expression and blockade of bioactive IL-23 and IL-12 production without affecting cellular viability or DCs maturation. Inhibition of IL-23 and IL-12 was associated with increased IL-10 and decreased TNF-alpha production. Furthermore, transfected DCs were poor allostimulators in the MLR. Our results demonstrate that an abnormal Th1 bias in DCs from MS patients related to IL-23 exists, and that antisense oligonucleotides specific to IL-23 can be used for immune modulation by targeting DC gene expression.

Induction of RNA interference in dendritic cells

Dendritic cells (DC) reside at the center of the immunological universe, possessing the ability both to stimulate and inhibit various types of responses. Tolerogenic/regulatory DC with therapeutic properties can be generated through various means of manipulations in vitro and in vivo. Here we describe several attractive strategies for manipulation of DC using the novel technique of RNA interference (RNAi). Additionally, we overview some of our data regarding yet undescribed characteristics of RNAi in DC such as specific transfection strategies, persistence of gene silencing, and multi-gene silencing. The advantages of using RNAi for DC genetic manipulation gives rise to the promise of generating tailor-made DC that can be used effectively to treat a variety of immunologically mediated diseases.

Combined activation of innate and T cell immunity for recognizing immunomodulatory properties of therapeutic agents

Complex syndromes such as atherosclerosis and type 2 diabetes are disorders that are associated with inflammatory processes involving innate and adaptive immunity. Emerging knowledge about the pathological consequences of immune imbalances in a wide range of disease settings is expected to help to identify novel therapeutic targets. However, current test systems for immunomodulatory drugs tend to be too simplistic, as they rely only on cells of the innate- or the adaptive-immune system, or they are complex, in vivo models, which are not suitable for screening purposes. Using a modified mixed lymphocyte culture (MMLC) assay for combined analysis of innate and adaptive immunity, we show that this assay is very sensitive for the presence of low concentrations of immunomodulatory agents. Low-dose lipopolysaccharide stimulation of cells from two unrelated donors yields a strong cytokine response including interleukin (IL)-12 and IL-18, which induce interferon-gamma as a potential analysis parameter. As the MMLC assay is based on the mutual interaction of cells of the innate and adaptive immunity, it enables the monitoring of cytokine release under almost physiological conditions and might be of interest for the characterization of known and novel drugs concerning their immunomodulatory potency.

Immune modulation by silencing IL-12 production in dendritic cells using small interfering RNA

RNA interference is a mechanism of posttranscriptional gene silencing that functions in most eukaryotic cells, including human and mouse. Specific gene silencing is mediated by short strands of duplex RNA of approximately 21 nt in length (termed small interfering RNA or siRNA) that target the cognate mRNA sequence for degradation. We demonstrate here that RNAi can be used for immune modulation by targeting dendritic cell (DC) gene expression. Transfection of DC with siRNA specific for the IL-12 p35 gene resulted in potent suppression of gene expression and blockade of bioactive IL-12 p70 production without affecting unrelated genes or cellular viability. Inhibition of IL-12 was associated with increased IL-10 production, which endowed the DC with the ability to stimulate production of Th2 cytokines from allogenic T cells in vitro. Furthermore, siRNA-silenced DC lacking IL-12 production were poor allostimulators in MLR. IL-12-silenced and KLH-pulsed DC polarized the immune response toward a Th2 cytokine profile in an Ag-specific manner. These data are the first to demonstrate that RNA interference is a potent and specific tool for modulating DC-mediated immune responses.

HIV-1 gp120 modulates the immunological function and expression of accessory and co-stimulatory molecules of monocyte-derived dendritic cells

Initiation of a primary immune response requires antigen specific CD4(+) T helper (T(h)) cells to assist in priming of CD8(+) cytotoxic T cell (CTL) activity. This is optimal when T(h) cells and CTL recognize antigen when presented to them by a dendritic cell (DC) in the context of major histocompatibility complex (MHC) class I and class II complexes. We have hypothesized that human DC exposed to HIV-1 gp120 IIIB envelope glycoprotein may activate or alter the immunological activation of DCs. Our findings have led us to conclude that HIV-1 gp120 LAV/IIIB activates monocyte-derived DC when they are in their immature state while HIV-1 gp120 exhibits highly selective effects on mature DC. We have observed that following maturation of DCs with lipopolysaccharide (LPS) that they are less susceptible to the modulatory effects of gp120. Although HIV-1 gp120 activates immature DC, it does so in a manner that abrogates their normal function in host immune responses and consequently disturbs the homeostatic balance of host immune response to infection. We suggest that HIV-1 gp120 may support sustained productive infection and transinfection of activated T cells that cluster with gp120-activated DC. We believe that these are promoted by mechanisms that are dependent, at least in part, on altered cytokine responses, enhanced expression of cellular adhesion molecules and augmented DC-mediated activation of T cells in nonspecific and antigen-specific immune reactivities. Consequently, HIV-1 gp120 may actively contribute to the immunopathogenesis of AIDS.

Effect of histamine on intercellular adhesion molecule-1 expression and production of interferon-gamma and interleukin-12 in mixed lymphocyte reaction stimulated with interleukin-18

BACKGROUND

Interleukin (IL)-18 was identified as an interferon (IFN)-gamma-inducing factor and was demonstrated to up-regulate the expression of intercellular adhesion molecule (ICAM)-1 on human monocytes. In organ transplantation, elevation of plasma IL-18 levels has been reported during acute rejection. In the present study, we examined the effect of IL-18 on human mixed lymphocyte reaction (MLR), an in vitro model of acute rejection after organ transplantation. We also investigated the modulatory effects of histamine on IL-18 action because histamine has been demonstrated to be a modulator of IL-18 effect and a mediator of inflammation.

METHODS

We measured the expression of ICAM-1 on human monocytes in MLR in the presence or absence of IL-18 by flow cytometer and determined the associated production of IFN-gamma and IL-12 by ELISA. The modulatory effects of histamine and the relevant histamine receptor subtypes were characterized pharmacologically.

RESULTS

The expression of ICAM-1 on monocytes in MLR was markedly enhanced by the addition of IL-18 in a concentration- and time-dependent manner. In parallel to ICAM-1 up-regulation, IL-18 significantly enhanced the production of IFN-gamma and IL-12 in MLR. Histamine concentration-dependently inhibited ICAM-1 expression and cytokine production in MLR stimulated with IL-18, whereas histamine alone did not show any effects on these responses in the absence of IL-18. The effects of histamine on both ICAM-1 expression and cytokine production were mimicked by the selective H2-receptor agonists 4-methylhistamine and dimaprit and were antagonized by the H2-receptor antagonist famotidine but not by H1- and H3-receptor antagonists.

CONCLUSION

IL-18 strongly enhanced human MLR with respect to ICAM-1 expression and cytokine production. The fact that histamine could inhibit the IL-18-stimulated MLR implies that immunomodulation by histamine and selective H2-receptor agonists may have an important role in future immunosuppressive strategies.

IL-18-independent cytotoxic T lymphocyte activation and IFN-gamma production during experimental acute graft-versus-host disease

Acute graft-versus-host disease (GvHD) is a serious complication after allogeneic bone marrow transplantation. Donor-derived T cells infiltrate recipient target organs and cause severe tissue damage, often leading to death of the affected patient. Tissue destruction is a direct result of donor CD8+ T cell activation and cell-mediated cytotoxicity. IL-18 is a novel pro-inflammatory cytokine with potent T(h)1 immune response-promoting and cytotoxic T lymphocyte (CTL)-inducing activity. IL-18 is strongly induced in experimental mouse models and human patients with acute GvHD. However, the precise role of IL-18 in the development of acute GvHD is still unknown. In this study, we have used IL-18-binding protein, a soluble IL-18 decoy receptor, to specifically neutralize IL-18 in vivo and in vitro. Our results demonstrate that IL-18 is induced during GvHD. However, its effect in the induction of GvHD appears to be redundant, since neutralization of IL-18 does not alter any disease parameter analyzed. Our study further shows that IFN-gamma production and CTL induction upon activation by T cell mitogens or by alloantigen does not involve IL-18-mediated amplification, in contrast to lipopolysaccharide-induced IFN-gamma production. We conclude that IL-18 expression correlates with the course of GvHD; however, its effect is dispensable for IFN-gamma and CTL induction for the initiation phase of this disease, most likely due to direct, IL-18-independent, CTL activation.

Effect of steroids on lipopolysaccharide/interleukin 2-induced interleukin 18 production in peripheral blood mononuclear cells

Interleukin (IL) 18, a powerful inducer of the immunoregulatory cytokine interferon-gamma (IFN-gamma), presents upstream of the cytokine activation cascade in the inflammatory response. The anti-inflammatory properties of steroids permit their use in various conditions, although effects are transient and pathological states are not fully relieved by short-term steroidal use. We examined the effect of lipopolysaccharide (LPS)/IL-2 on the cytokine cascade in human peripheral blood mononuclear cells (PBMCs). We also examined the effect of steroids on LPS/IL-2-induced cytokine production in human PBMCs taken from healthy volunteers. Cell-free supernatant fractions were assayed for IL-18, IL-12, IL-2, IFN-gamma and IL-10 protein, using enzyme-linked immunosorbent assays, and synergy between LPS and IL-2 in enhanced production of IL-18 was observed. Steroids suppressed the production of IL-18 and other secondary cytokines in LPS/IL-2-stimulated PBMCs, in a concentration- and time-dependent manner, although inhibition was incomplete even at high concentrations. Effects of steroid treatment on expression of membrane-bound LPS receptor antigen (mCD14) and intercellular adhesion molecule-1 (ICAM-1) in PBMCs were studied by flow cytometric analysis. Steroid treatment up-regulated mCD14 expression in a concentration-dependent manner, with no effect on ICAM-1 expression. These results suggest that the incomplete counteraction of steroids in the LPS/IL-2-initiating cytokine cascade is due, at least partly, to the up-regulation of mCD14 by steroid preparations, which increases susceptibility to bacterial endotoxins.

Regulation of T cell cytokine production by dendritic cells generated in vitro from hematopoietic progenitor cells

When dendritic cells (DC) present antigens to T cells, reciprocal cellular interactions occur that lead to cytokine production. This cytokine response is regulated by specific properties of DC, notably their maturation/activation status and perhaps their origin. The latter possibility prompted us to determine if DC produced along distinct developmental pathways induced distinct T cell responses. Hematopoietic progenitor cells with the potential to differentiate into multiple lineages of cells were induced to differentiate into DC along two pathways. One leads to the formation of lymphoid-related DC but not of monocyte-derived DC and is induced by culture of CD34(+) cells with flt-3 ligand (F), c-kit ligand (K), GM-CSF (Gm), IL-1beta ("1"), and IL-7 ("7") (FKGm17). Another pathway with distinct molecular requirements supports in part monocyte-derived DC and is induced by the cytokines F, K, Gm, TNF-alpha (T), and IL-4 ("4") (FKGmT4). DC produced along these two pathways were isolated by flow cytometry and compared. They differed only slightly in phenotype and morphology and both induced Th1-type cytokine production in MLR (mixed lymphocyte reactions). However, on a cell-per-cell basis, FKGm17-DC produced more IL-18 or IL-12 and induced more IFN-gamma by T cells in MLR. Such superior properties were not intrinsically determined by the origin of the DC but were induced by FKGm17 cytokines. We conclude that lymphoid-related DC have the potential to induce Th1 T cell responses but that environmental signals strongly influence T-cell-stimulating properties of DC.