Inhibition of IL-12 production in human monocyte-derived macrophages by TNF

PK1/EG-VEGF induces monocyte differentiation and activation

Macrophages exist as sentinels in innate immune response and react by expressing proinflammatory cytokines and up-regulating antigen-presenting and costimulatory molecules. We report a novel function for prokineticin-1 (PK1)/endocrine gland-derived vascular endothelial growth factor. Screening of murine tissue sections and cells for specific binding site leads to the identification of macrophages as an in vivo cellular target for PK1. We demonstrate PK1 induces differentiation of murine and human bone marrow cells into the monocyte/macrophage lineage. Human peripheral blood monocytes respond to PK1 by morphological changes and down-regulation of B7-1, CD14, CC chemokine receptor 5, and CXC chemokine receptor 4. Monocytes treated with PK1 have elevated interleukin (IL)-12 and tumor necrosis factor alpha and down-regulated IL-10 production in response to lipopolysaccharide. PK1 induces a distinct monocyte-derived cell population, which is primed for release of proinflammatory cytokines that favor a T helper cell type 1 response.

Recombinant guinea pig tumor necrosis factor alpha stimulates the expression of interleukin-12 and the inhibition of Mycobacterium tuberculosis growth in macrophages

Tumor necrosis factor alpha (TNF-alpha) plays an important role in the host immune response to infection with the intracellular pathogen Mycobacterium tuberculosis. It is essential for the formation of protective tuberculous granulomas and regulates the expression of other cytokines which contribute to a protective immune response. Interleukin-12 (IL-12) is known to promote a Th1 response, which is essential for antimycobacterial resistance. Recombinant guinea pig TNF-alpha (rgpTNF-alpha) protein (17 kDa) was purified, and its bioactivity was confirmed by its cytotoxicity for L929 fibroblasts. High titers of polyclonal anti-gpTNF-alpha antibody were obtained by immunization of rabbits. Resident alveolar and peritoneal macrophages were isolated from guinea pigs and infected with either the H37Ra or H37Rv strain of M. tuberculosis. The mRNA levels for TNF-alpha and IL-12 p40 were measured using real-time PCR. IL-12 p40 mRNA was up-regulated in a dose-dependent manner by rgpTNF-alpha alone. In infected macrophages, a lower dose of rgpTNF-alpha intensified the mRNA levels of TNF-alpha and IL-12 p40. However, higher doses of rgpTNF-alpha suppressed TNF-alpha and IL-12 p40 mRNA. The antimycobacterial activity of macrophages was assessed by metabolic labeling of M. tuberculosis with [3H]uracil. Resident alveolar and peritoneal macrophages treated with anti-gpTNF-alpha antibody to block endogenous TNF-alpha exhibited increased intracellular mycobacterial growth. These data suggest that the dose of TNF-alpha is crucial to the stimulation of optimal expression of protective cytokines and that TNF-alpha contributes to the control of mycobacterial replication to promote host resistance against M. tuberculosis.

Disruption of MAP kinase activation and nuclear factor binding to the IL-12 p40 promoter in HIV-infected myeloid cells

Progressive immunodeficiency in HIV infection is paralleled by a decrease in IL-12 production, a cytokine crucial for cellular immune function. Here we examine the molecular mechanisms by which HIV infection suppresses IL-12 p40 expression. HIV infection of THP-1 myeloid cells resulted in decreased LPS-induced nuclear factor binding to the NF-kappaB, AP-1, and Sp1 sites of the IL-12 p40 promoter. By site-directed mutagenesis we determined that each of these sites was necessary for transcriptional activation of the IL-12 p40 promoter. Binding of NF-kappaB p50, c-Rel, p65, Sp1, Sp3, c-Fos, and c-Jun proteins to their cognate nuclear factor binding sites was somewhat impaired by HV infection, although a role for other as yet unidentified factors cannot be dismissed. The cellular levels of these transcription factors were unaffected by HIV infection, with the exception of a decrease in expression of NF-kappaB p65, consistent with the observed decrease in its binding to the IL-12 p40 promoter following HIV infection. Analysis of regulation of upstream LPS-induced MAP kinases demonstrated impaired phosphorylation of JNK and p38 MAPK, and suppressed phosphorylation and degradation of IkappaBalpha following HIV infection. These results suggest that alterations in nuclear factor binding to numerous sites in the IL-12 p40 promoter, together may contribute to the suppression in IL-12 p40 transcription previously reported. These effects on nuclear factor binding may be a direct effect of HIV infection on the IL-12 p40 promoter, or may occur indirectly as a consequence of altered MAP kinase activation.

Activation and repression of interleukin-12 p40 transcription by erythroid Kruppel-like factor in macrophages

Transcription of interleukin (IL)-12 p40 in myeloid cells is attributed to the recruitment of multiple activated transcription factors such as nuclear factor kappaB (NFkappaB), CCAAT enhancer-binding protein beta, ets-2, PU.1, and so forth. We now provide the first description of the human erythroid Kruppel-like factor (EKLF) in human primary macrophages and identify the role of EKLF in IL-12 p40 expression. EKLF-specific binding to the CACCC element (-224 to -220) on the human IL-12 p40 promoter was observed in resting human primary macrophages. Functional analysis of the CACCC element revealed a dependent role for EKLF binding in activating IL-12 p40 transcription in resting RAW264.7 cells, whereas EKLF overexpression in the presence or absence of this element repressed IL-12 p40 transcription in interferon gamma/lipopolysaccharide-stimulated RAW264.7 cells. Murine endogenous IL-12 p40 mRNA was consistently induced by overexpressed EKLF in resting RAW264.7 cells, whereas EKLF suppressed IL-12 p40 expression in activated RAW264.7 cells. Modulation of nuclear binding activities at the IL-12 p40 NFkappaB half-site was induced by EKLF for down-regulation of IL-12 p40 transcription in activated RAW264.7 cells, but no effect of EKLF on NFkappaB activity was observed in resting RAW264.7 cells. Taken together, we identify EKLF as a transcription factor in macrophages able to regulate IL-12 p40 transcription depending on the cellular activation status. The bifunctional control of IL-12 p40 by EKLF and its modulation of NFkappaB support a potential function for this factor in orchestrating IL-12 p40 production in macrophages.

Differential regulation of interleukin (IL)-12 p35 and p40 gene expression and interferon (IFN)-gamma-primed IL-12 production by IFN regulatory factor 1

Interleukin (IL)-12 is a heterodimeric cytokine consisting of the p40 and p35 chains encoded on separate chromosomes. Coordinated expression of the two constituent genes is crucial for appropriate immune responses in timing, location, and magnitude. Interferon (IFN)-gamma priming of IL-12 production by macrophages represents an important physiological process in vivo for escalated cellular response to microbial infections. We provide evidence that IFN regulatory factor (IRF)-1-deficient macrophages have a selective impairment in mRNA synthesis of IL-12 p35 but not the p40 gene, and a strong deficiency in the production of IL-12 p70 but not p40. We demonstrate that the levels of IL-12 p35 protein stimulated by IFN-gamma and lipopolysaccharide (LPS) correspond to those of its mRNA, and that the nuclear factor kappaB signaling pathway is essential for the induction of IL-12 p35 transcription by LPS. IRF-1 plays a major role in the transcriptional activation of the IL-12 p35 gene, but not of the p40 gene, by physically interacting with an inverted IRF element within the IL-12 p35 promoter upon IFN-gamma activation. Moreover, IRF-1-mediated transcriptional activation of the p35 promoter requires the cooperation of two adjacent Sp1 elements. Thus, IRF-1 acts as a critical component of IFN-gamma signaling in the selective activation of IL-12 p35 transcription in synergy with LPS-mediated events.

Immature macrophages derived from mouse bone marrow produce large amounts of IL-12p40 after LPS stimulation

Production of IL-12 is an important indicator of the macrophage's ability to regulate immune responses. In this study, we investigated the IL-12 production by macrophages in different developmental stages. To this end, macrophages were generated in vitro from precursors stimulated with M-CSF, GM-CSF or IL-3. Density separation yielded populations enriched in different maturation stages. Invariably, only cells banding at the 40-50% Percoll interface produced large amounts of IL-12p40 when stimulated with LPS, whereas only low levels of IL-12p70 were produced. These cells represented immature macrophages, as indicated by the absence of precursor markers CD31/ER-MP12, Ly-6C/ER-MP20 and ER-MP58, and by the low level of expression of mature-cell markers like ER-HR3, scavenger receptor and CD11b/Mac-1. Upon further maturation, the macrophages' ability to produce IL-12p40 decreased, coinciding with increased nitric oxide production upon LPS stimulation. These results show that immature macrophages produce high levels of IL-12p40 and thus may either contribute to IL-12p70 production or regulate it.

Selective suppression of IL-12 production by human herpesvirus 6

Human herpesvirus 6 (HHV-6) is a potentially immunosuppressive agent that has been suggested to act as a cofactor in the progression of HIV disease. Exposure of human macrophages to HHV-6A or HHV-6B profoundly impaired their ability to produce interleukin 12 (IL-12) upon stimulation with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS). By contrast, the production of tumor necrosis factor-alpha (TNF-alpha); regulated on activation, normal T-cell expressed and secreted (RANTES); and macrophage inflammatory protein 1 beta (MIP-1 beta) was not negatively affected. To exclude the involvement of IL-12-suppressive cytokines, such as IL-10 and TNF-alpha, the viral stocks were fractionated by ultra-centrifugation. The bulk of the suppressive activity was recovered within the virion-rich pelleted fraction that was virtually devoid of such cytokines. IL-12 suppression was independent of viral replication, and the effect was not abrogated upon ultraviolet-light inactivation of the viral inoculum. The mechanism of HHV-6-mediated IL-12 suppression was investigated by RNase protection assays, which demonstrated unaltered levels of IL-12 p35 mRNA and only a modest reduction in p40 mRNA, which was insufficient to account for the near-complete loss of both extracellular and intracellular IL-12 protein. Moreover, both the IFN-gamma and the LPS signaling pathways were intact in HHV-6-treated cells. These data suggest that HHV-6 can dramatically affect the generation of effective cellular immune responses, providing a novel potential mechanism of HHV-6-mediated immunosuppression.

Airway epithelia regulate expression of human beta-defensin 2 through Toll-like receptor 2

The goal of this study is to investigate whether TLR2 mediates hBD2 induction through NF-kappaB in response to bacterial components in the human airway epithelia. We showed that hTLR2 is expressed in the airway epithelial cells by immunohistochemical staining and RT-PCR. The biology of hTLR2 in this context was studied initially in 293 cells transfected with a plasmid expressing hTLR2 together with an hBD2 promoter-driven luciferase reporter (hBD2-promoter-LUC). Upon incubation with lipoteichoic acid (LTA), the major cell wall component of gram-positive bacteria, luciferase activity was greatly increased compared with mock stimulation. Analysis of mutation constructs of the hBD2 promoter revealed that NF-kappaB sites are important for hTLR2-mediated hBD2 up-regulation upon LTA stimulation. When hBD2-promoter-LUC was transfected into primary human airway epithelia cells (EC), the luciferase activity was greatly increased upon LTA stimulation compared with mock stimulation. The hBD2 promoter mutation constructs were also tested in EC, which confirmed the studies in 293 cells. When a plasmid expressing a dominant-negative mutant of hTLR2 was co-transfected with hBD2-promoter-LUC into EC, LTA could not stimulate hBD2 expression. These data provide convincing evidence that up-regulation of hBD2 can be induced through hTLR2-mediated NFkappaB/IkappaB pathway in the human airway epithelial cells.

Cumulative Toll-like receptor activation in human macrophages treated with whole bacteria

Purified components from bacteria selectively activate Toll-like receptors (TLR), leading to shared and unique responses in innate immune cells. Whole bacteria contain agonists for multiple TLR and induce a common macrophage activation program of transcription. It is not known, however, whether the stimulation of specific TLR by whole bacteria results in differential activation of the innate immune system. We evaluated gene expression data from human macrophages and found a unique gene expression profile induced by Gram-negative bacteria. In contrast, Gram-positive bacteria evoked few specific alterations in gene expression. LPS, a TLR4-specific ligand, was sufficient to elicit the distinct expression profile observed with Gram-negative bacteria. TLR4 activation regulated gene expression by both an IFN-dependent and an IFN-independent mechanism, illustrated by I-TAC and IL-12 p70, respectively. IL-12 p70 was produced by cells in whole blood exposed to Gram-negative bacteria, demonstrating faithful reproduction of the macrophage response in mixed populations of cells and identifying a potential diagnostic marker of infection. Our results show that the macrophage response to bacteria is dominated by the accumulated input from multiple TLR. For macrophages exposed to Gram-negative bacteria, gene expression changes encompass those induced by Gram-positive bacteria plus a distinct TLR4 response. This distinct TLR4 response may provide the basis to diagnose clinical Gram-negative infections.

Fever-like thermal conditions regulate the activation of maturing dendritic cells

Fever is one of the most frequent clinical signs encountered in pathology, especially with respect to infectious diseases. It is currently thought that the role of fever on immunity is limited to activation of innate immunity; however, its relevance to activation of adaptive immunity remains unclear. Dendritic cells (DCs) that behave as sentinels of the immune system provide an important bridge between innate and adaptive immunity. To highlight the role of fever on adaptive immunity, we exposed murine bone marrow-derived lipopolysaccharide (LPS)- or live bacteria-maturing DCs over a 3-h period to 37 degrees C or to fever-like thermal conditions (39 degrees C or 40 degrees C). At these three temperatures, we measured the kinetics of cytokine production and the ability of DCs to induce an allogeneic mixed lymphocyte reaction. Our results show that short exposure of DCs to temperatures of 39 degrees C or 40 degrees C differentially increased the secretion of interleukin (IL)-12p70 and decreased the secretion of IL-10 and tumor necrosis factor alpha by maturing DCs. These fever-like conditions induced a regulation of cytokine production at the single-cell level. In addition, short-term exposed LPS-maturing DCs to 39 degrees C induced a stronger reaction with allogeneic CD4(+) T cells than maturing DCs incubated at 37 degrees C. These results provide evidence that temperature regulates cytokine secretion and DC functions, both of which are of particular importance in bacterial diseases.

Activation of terminally differentiated human monocytes/macrophages by dengue virus: productive infection, hierarchical production of innate cytokines and chemokines, and the synergistic effect of lipopolysaccharide

Dengue virus (DV) primarily infects blood monocytes (MO) and tissue macrophages (M phi). We have shown in the present study that DV can productively infect primary human MO/M phi regardless of the stage of cell differentiation. After DV infection, the in vitro-differentiated MO/M phi secreted multiple innate cytokines and chemokines, including tumor necrosis factor alpha, alpha interferon (IFN-alpha), interleukin-1 beta (IL-1 beta), IL-8, IL-12, MIP-1 alpha, and RANTES but not IL-6, IL-15, or nitric oxide. Secretion of these mediators was highlighted by distinct magnitude, onset, kinetics, duration, and induction potential. A chemokine-to-cytokine hierarchy was noted in the magnitude and induction potential of secretion, and a chemokine-to-cytokine-to-chemokine/Th1 cytokine cascade could be seen in the production kinetics. Furthermore, we found that terminally differentiated MO/M phi cultured for more than 45 days could support productive DV infection and produce innate cytokines and chemokines, indicating that these mature cells were functionally competent in the context of a viral infection. In addition, DV replication in primary differentiated human MO/M phi was enhanced and prolonged in the presence of lipopolysaccharide (LPS), and LPS-mediated synergistic production of IFN-alpha could be seen in DV-infected MO/M phi. The secretion of innate cytokines and chemokines by differentiated MO/M phi suggests that regional accumulation of these mediators may occur in various tissues to which DV has disseminated and may thus result in local inflammation. The LPS-mediated enhancement of virus replication and synergistic IFN-alpha production suggests that concurrent bacterial infection may modulate cytokine-mediated disease progression during DV infection.

Selective interleukin-12 synthesis defect in 12/15-lipoxygenase-deficient macrophages associated with reduced atherosclerosis in a mouse model of familial hypercholesterolemia

Targeted gene disruption or overexpression of 12/15-lipoxygenase in mice on the genetic background of apolipoprotein E or low density lipoprotein-receptor (LDL-R) deficiency has implicated 12/15-lipoxygenase in atherogenesis. The data support indirectly a role for 12/15-lipoxygenase in the oxidative modification of low density lipoprotein. In this study we set out to explore other potential mechanisms for 12/15-lipoxygenase in atherosclerosis using apolipoprotein B mRNA editing catalytic polypeptide-1/LDL-R double-deficient mice, a model highly related to the human condition of familial hypercholesterolemia. 12/15-Lipoxygenase deficiency in this strain led to approximately 50% decrease in aortic lesions in male and female mice at 8 months on a chow diet in the absence of cholesterol differences. While studying 12/15-lipoxygenase-deficient macrophages in culture, we discovered a remarkable selective defect (75-90% decrease) in interleukin-12 production but not in tumor necrosis factor-alpha or nitric oxide release, in response to lipopolysaccharide in the presence or absence of interferon-gamma priming. The lipopolysaccharide/interferon-gamma response was associated with a 33-50% decrease in nuclear interferon consensus sequence-binding protein, which is consistent with interferon consensus sequence-binding protein containing protein complex-dependent regulation of the interleukin-12 p40 gene. The decrease in interleukin-12 production was recapitulated in vivo in mouse aortas of the triple knockout group and was reflected in a marked decrease in interferon-gamma expression. The data provide support for a novel mechanism linking the 12/15-lipoxygenase pathway to a known immunomodulatory Th1 cytokine in atherogenesis.

Regulation of interleukin-12 production in antigen-presenting cells

Interleukin-12 is a cytokine produced by antigen-presenting cells that is essential for host defense against intracellular microbial infection and control of malignancy by virtue of its ability to stimulate both innate and adaptive immune effector cells. The immune potentiating capacity of IL-12 and its mandatory requirement in host defense predispose it to rigorous regulation. The time, localization, and magnitude of IL-12 production during an immune response strongly influence the type, extent, and, ultimately, the fate of the response. Disturbance of this evolutionarily maintained "balance of power" frequently leads to immunologic disorders. This article reviews the intricate pathways that have been uncovered in which IL-12 production is modulated by numerous pathogens and immunological regulators. The understanding of IL-12 regulation in physiological settings will undoubtedly lend valuable support to the design of therapeutic applications of IL-12.

Tuberculosis unleashed: the impact of human immunodeficiency virus infection on the host granulomatous response to Mycobacterium tuberculosis

The granuloma plays a critical role in the host immune response to Mycobacterium tuberculosis, containing the organism and confining it in a latent state in most infected individuals. Indeed, approximately one-third of the world's population has latent M. tuberculosis infection. However, over the past decade, the human immunodeficiency virus type 1 (HIV-1) pandemic has profoundly affected the incidence and clinicopathological features of tuberculosis. This review examines the immunological mechanisms whereby HIV-1 impairs the establishment, maintenance and function of the tuberculous granuloma.

Suppression of IL-12 production by soluble CD40 ligand: evidence for involvement of the p44/42 mitogen-activated protein kinase pathway

IL-12 is a key cytokine in skewing immune responses toward Th1-like reactions. Human monocytes/macrophages produce high amounts of bioactive IL-12 when a priming signal (IFN-gamma or GM-CSF) precedes a second signal (e.g., LPS). We and others have previously shown that preincubation with LPS before this stimulation procedure can efficiently and selectively suppress the production of IL-12 by human monocytes. In this study, we show that an almost complete suppression of IL-12 production can also be observed after preincubation of monocytes with costimulatory cell surface molecules that bind to members of the TNFR superfamily (CD40 ligand, TNF-related activation-induced cytokine (TRANCE)). The suppression of IL-12 was observable on the mRNA and protein levels and was not due to endogenous production of known IL-12 antagonists (i.e., IL-10, IL-4, and PGE(2)), to an increased number of cells undergoing apoptosis, nor to down-regulation of the IFN-gamma or CD40 receptor. Cell surface expression of the costimulatory molecules CD80 and CD86 was not reduced by the preincubation procedure, and only a moderate reduction of IL-6 production was observed. Several studies have identified signal transduction pathways that are activated by CD40 signaling, including activation of mitogen-activated protein kinases. The presence of the extracellular signal-related kinase-specific mitogen-activated protein kinase kinase 1/2-specific inhibitors PD98059 and U0126 abrogated suppression induced by sCD40 ligand or other second signals. This indicates that activation of extracellular signal-regulated kinase 1/2 contributes to the underlying mechanism of IL-12 suppression. This mechanism may be relevant in other inflammatory responses and may help to develop therapeutic strategies in Th1-mediated diseases.

Regulation of CD154-induced interleukin-12 production in synovial fluid macrophages

Interleukin (IL)-12, being a major cytokine that induces T helper (Th) 1 differentiation and inflammatory response, has been postulated to be an important mediator of synovial inflammation in rheumatoid arthritis (RA). However, the regulation of IL-12 production in RA has not been elucidated. Our knowledge is mainly based on studies of the production of IL-12p40 and not the functional IL-12p70 heterodimer. We have studied the CD154-induced IL-12p40 and IL-12p70 production by synovial fluid (SF) macrophages from patients with RA. CD40 ligation induced the secretion of IL-12p40 but not IL-12p70. The observed increase in IL-10 and tumor necrosis factor (TNF)-alpha production indicated that SF macrophages responded to CD40 ligation. The expression of p40 mRNA was increased significantly and remained upregulated after CD40 ligation, whereas the increase of p35 transcript expression was observed only transiently and at a lower level. We further observed that dendritic cells (DCs) derived in vitro from SF macrophages produced IL-12p70. Most importantly, IL-4 and IL-13 primed SF macrophages to produce IL-12p70, whereas IFN-gamma was not observed to activate IL-12p70 production in these cells, in contrast with normal peripheral blood monocytes. These results provide novel information about the regulation of IL-12p70 production and the function of the cytokine network in RA.

Critical role for tumor necrosis factor alpha in controlling the number of lumenal pathogenic bacteria and immunopathology in infectious colitis

Infection of mice with the intestinal bacterial pathogen Citrobacter rodentium results in colonic mucosal hyperplasia and a local Th1 inflammatory response similar to that seen in mouse models of inflammatory bowel disease. In these latter models, and in patients with Crohn's disease, neutralization of tumor necrosis factor alpha (TNF-alpha) is of therapeutic benefit. Since there is no information on the role of TNF-alpha in either immunity to noninvasive bacterial pathogens or on the role of TNF-alpha in the immunopathology of infectious colitis, we investigated C. rodentium infection in TNFRp55(-/-) mice. In TNFRp55(-/-) mice, there were higher colonic bacterial burdens, but the organisms were cleared at the same rate as C57BL/6 mice, showing that TNF-alpha is not needed for protective antibacterial immunity. The most striking feature of infection in TNFRp55(-/-) mice, however, was the markedly enhanced pathology, with increased mucosal weight and thickness, increased T-cell infiltrate, and a markedly greater mucosal Th1 response. Interleukin-12 p40 transcripts were markedly elevated in C. rodentium-infected TNFRp55(-/-) mice, and this was associated with enhanced mucosal STAT4 phosphorylation. TNF-alpha is not obligatory for protective immunity to C. rodentium in mice; however, it appears to play some role in downregulating mucosal pathology and Th1 immune responses.

Differential response of the murine IL-12 p35 gene to lipopolysaccharide compared with interferon-gamma and CD40 ligation

Expression of the heterodimeric cytokine interleukin-(IL-)12 is induced by pattern recognition receptors responding to microbial stimuli such as lipopolysaccharide (LPS) and products of the immune system such as interferon-gamma (IFN-gamma) and CD40L. The formation of bioactive IL-12 requires equimolar synthesis of p35 and p40 subunits. However, p35 expression limits the amount of IL-12 formed. Transcription of the gene for the p35 subunit of IL-12 initiates within the first exon, an alternate first exon (exon 1a), or second exon. Here we show that LPS and IFN-gamma/CD40 ligation increase the amount of total p35 mRNA in splenic adherent cells (SAC) to a similar extent. However, the exon 1 transcript was a smaller fraction of total p35 mRNA in IFN-gamma/CD40-stimulated cells than in unstimulated or LPS-stimulated cells. Despite comparable levels of total p35 mRNA, LPS-induced p35 exon 1 transcripts led to significantly more bioactive IL-12 from SAC than IFN-gamma/CD40-induced exon 1a/exon 2 transcripts as measured by ELISA. The data suggest that LPS-inducible p35 synthesis from exon 1 p35 transcripts leads to greater amount of bioactive IL-12 than IFN-gamma/CD40-induced p35 expression from alternate p35 exon 1a/exon 2 transcripts.

Immunotherapy of multiple sclerosis: the end of the beginning

Currently available medicines approved for use in Europe and North America reduce the relapse rate in relapsing/remitting multiple sclerosis by about 30%. These medications may be no more efficacious than intermittent use of corticosteroids at the time of relapse. New directions for therapy of multiple sclerosis include blockade of alpha4 integrin, the use of altered peptide ligands, inhibition of Th1 cytokines, and DNA vaccination.

Down-regulation of CD28 expression by TNF-alpha

Aging and chronic inflammatory syndromes, such as rheumatoid arthritis, are associated with high frequencies of CD4(+)CD28(null) T cells, which are rarely seen in healthy individuals younger than 40 years. Inasmuch as rheumatoid arthritis and aging are also associated with elevated levels of TNF-alpha, we examined whether this proinflammatory cytokine influences CD28 expression. Incubation of T cell lines and clones as well as Jurkat cells with TNF-alpha induced a reduction in the levels of cell surface expression of CD28. This effect of TNF-alpha was reversible; however, continuous culture of CD4(+)CD28(+) T cell clones in TNF-alpha resulted in the appearance of a CD28(null) subset. In reporter gene bioassays, TNF-alpha was found to inhibit the activity of the CD28 minimal promoter. Inactivation of the promoter was accompanied by a marked reduction in DNA-protein complex formation by two DNA sequence motifs corresponding to the transcriptional initiator of the CD28 gene. Indeed, in vitro transcription assays showed that nuclear extracts from TNF-alpha-treated cells failed to activate transcription of DNA templates under the control of a consensus TATA box and the CD28 initiator sequences. In contrast, similar extracts from unstimulated T cells supported transcription. These results demonstrate that TNF-alpha directly influences CD28 gene transcription. We propose that the emergence of CD4(+)CD28(null) T cells in vivo is facilitated by increased production of TNF-alpha.

Acute cytokine response to systemic adenoviral vectors in mice is mediated by dendritic cells and macrophages

We investigated the cellular basis for secretion of inflammatory cytokines in mice following intravenous administration of adenoviral vectors (Ad). Serum inflammatory cytokines including interleukin-6 (IL-6), IL-12, and tumor necrosis factor-alpha (TNF-alpha) were detected as early as 6 h following intravenous injection of Ad-expressing Escherichia coli beta-galactosidase (Ad-lacZ). Ad-lacZ readily accumulated in the splenic marginal zone 1 h after intravenous infusion, where both dendritic cells (DCs) and macrophages were transduced and activated within 6 h. Flow cytometric analyses showed that the expression of Ia and CD86 antigens was markedly enhanced on splenic DCs indicating their activation in vivo by Ad-lacZ. Upon ex vivo culture, these early-activated splenic DCs spontaneously produced high levels of IL-6 and IL-12. By contrast, activated splenic macrophages spontaneously secreted only IL-6. Elimination of tissue macrophages and splenic DCs in vivo considerably reduced the early release of IL-12, IL-6, and TNF-alpha and significantly blocked the specific cellular immune response to Ad and the transgene product in vivo. Our findings indicate that preferential activation of DCs and macrophages may account for Ad-triggered acute inflammatory response in vivo in mice. Moreover, DCs and macrophages may play different roles in this process in terms of their abilities to produce distinct patterns of inflammatory cytokines.

The Th1 versus Th2 cytokine profile in cerebrospinal fluid after severe traumatic brain injury in infants and children

OBJECTIVE: To further characterize the Th1 (proinflammatory) vs. the Th2 (antiinflammatory) cytokine profile after severe traumatic brain injury (TBI) by quantifying the ventricular cerebrospinal fluid concentrations of Th1 cytokines (interleukin [IL]-2 and IL-12) and Th2 cytokines (IL-6 and IL-12) in infants and children. DESIGN: Retrospective study. SETTING: University children's hospital. PATIENTS: Twenty-four children hospitalized with severe TBI (admission Glasgow Coma Scale score, <13) and 12 controls with negative diagnostic lumbar punctures. INTERVENTIONS: All TBI patients received standard neurointensive care, including the placement of an intraventricular catheter for continuous drainage of cerebrospinal fluid. MEASUREMENTS AND MAIN RESULTS: Ventricular cerebrospinal fluid samples (n = 105) were collected for as long as the catheters were in place (between 4 hrs and 222 hrs after TBI). Cerebrospinal fluid samples were analyzed for IL-2, IL-4, IL-6, and IL-12 concentrations by enzyme-linked immunoassay. Peak and mean IL-6 (335.7 +/- 41.4 pg/mL and 259.5 +/- 37.6 pg/mL, respectively) and IL-12 (11.4 +/- 2.2 pg/mL and 4.3 +/- 0.8 pg/mL, respectively) concentrations were increased (p <.05) in children after TBI vs. controls (2.3 +/- 0.7 pg/mL and 1.0 +/- 0.5 pg/mL) for IL-6 and IL-12, respectively. In contrast, peak and mean IL-2 and IL-4 concentrations were not increased in TBI children vs. controls. Increases in the cerebrospinal fluid concentration of IL-6 were significantly associated with admission Glasgow Coma Scale score of </=4 and age of </=4 yrs. Increases in cerebrospinal fluid IL-4 and IL-12 were associated with child abuse as an injury mechanism (both p </=.05 vs. accidental TBI). CONCLUSIONS: This study confirms that IL-6 levels are increased in cerebrospinal fluid after TBI in infants and children. It is the first report of increased IL-12 levels in cerebrospinal fluid after TBI in infants and children. Further, it is the first to report on IL-2 and IL-4 levels in pediatric or adult TBI. These data suggest that selected members of both the Th1 and Th2 cytokine families are increased as part of the endogenous inflammatory response to TBI. Finally, in that both IL-6 and IL-12 (but neither IL-2 nor IL-4) can be produced by astrocytes and/or neurons, a parenchymal source for cytokines in the brain after TBI may be critical to their production in the acute phase after TBI.

Down-regulation of IL-12 p40 gene in Plasmodium berghei-infected mice

We analyzed the mechanism that causes suppression of IL-12 p40 gene induction during Plasmodium berghei infection. Although IL-12 together with IFN-gamma plays an important role in protection against pathogenic infection, the IL-12 p70 protein production of infected macrophages is lower than that by the uninfected macrophages. We showed in the present study that the induction of IL-12 p40 gene but not IL-12 p35 gene in macrophages of P. berghei-infected mice was profoundly inhibited. The inhibition was induced by interaction with macrophages that had contacted with P. berghei-infected erythrocytes and was mediated by a soluble factor, IL-10. There was comparable activation of NF-kappaB in uninfected and infected cells. The induction of IFN-regulatory factor-1 gene was comparable in transcription level in uninfected and infected cells, while the unidentified complex formation of IFN-regulatory factor-1 was observed in infected cells. Therefore, the inhibition of the IL-12 p40 gene induction appeared to be regulated at transcriptional regulation level of the gene.

IL-12 suppression during experimental endotoxin tolerance: dendritic cell loss and macrophage hyporesponsiveness

Endotoxin tolerance, the transient, secondary down-regulation of a subset of endotoxin-driven responses after exposure to bacterial products, is thought to be an adaptive response providing protection from pathological hyperactivation of the innate immune system during bacterial infection. However, although protecting from the development of sepsis, endotoxin tolerance also can lead to fatal blunting of immunological responses to subsequent infections in survivors of septic shock. Despite considerable experimental effort aimed at characterizing the molecular mechanisms responsible for a variety of endotoxin tolerance-related phenomena, no consensus has been achieved yet. IL-12 is a macrophage- and dendritic cell (DC)-derived cytokine that plays a key role in pathological responses to endotoxin as well as in the induction of protective responses to pathogens. It recently has been shown that IL-12 production is suppressed in endotoxin tolerance, providing a likely partial mechanism for the increased risk of secondary infections in sepsis survivors. We examined the development of IL-12 suppression during endotoxin tolerance in mice. Decreased IL-12 production in vivo is clearly multifactorial, involving both loss of CD11c(high) DCs as well as alterations in the responsiveness of macrophages and remaining splenic DCs. We find no demonstrable mechanistic role for B or T lymphocytes, the soluble mediators IL-10, TNF-alpha, IFN-alphabeta, or nitric oxide, or the NF-kappaB family members p50, p52, or RelB.

Interleukin 12 p40 production by barrier epithelial cells during airway inflammation

Human airway epithelial cells appear specially programmed for expression of immune response genes implicated in immunity and inflammation. To better determine how this epithelial system operates in vivo, we analyzed its behavior in mouse models that allow for in vitro versus in vivo comparison and genetic modification. Initial comparisons indicated that tumor necrosis factor alpha induction of epithelial intercellular adhesion molecule 1 required sequential induction of interleukin (IL)-12 (p70) and interferon gamma, and unexpectedly localized IL-12 production to airway epithelial cells. Epithelial IL-12 was also inducible during paramyxoviral bronchitis, but in this case, initial IL-12 p70 expression was followed by 75-fold greater expression of IL-12 p40 (as monomer and homodimer). Induction of IL-12 p40 was even further increased in IL-12 p35-deficient mice, and in this case, was associated with increased mortality and epithelial macrophage accumulation. The results placed epithelial cell overgeneration of IL-12 p40 as a key intermediate for virus-inducible inflammation and a candidate for epithelial immune response genes that are abnormally programmed in inflammatory disease. This possibility was further supported when we observed IL-12 p40 overexpression selectively in airway epithelial cells in subjects with asthma and concomitant increases in airway levels of IL-12 p40 (as homodimer) and airway macrophages. Taken together, these results suggest a novel role for epithelial-derived IL-12 p40 in modifying the level of airway inflammation during mucosal defense and disease.

TNF-alpha and IL-12: a balancing act in macrophage functioning

Tumor necrosis factor alpha (TNF-alpha) and interleukin 12 (IL-12) are two major macrophage-derived mediators of inflammatory responses in mammals. Increasing evidence suggests that TNF-alpha is a double-edged sword with both proinflammatory and anti-inflammatory propensities. This article discusses the inter-regulation of TNF-alpha and IL-12 and the impact on the function of macrophages in innate and adaptive immunity.

Kinetics of dendritic cell activation: impact on priming of TH1, TH2 and nonpolarized T cells

To prime immune responses, dendritic cells (DCs) need to be activated to acquire T cell stimulatory capacity. Although some stimuli trigger interleukin 12 (IL-12) production that leads to T helper cell type I (TH1) polarization, others fail to do so and favor TH2 polarization. We show that after activation by lipopolysaccharide, DCs produced IL-12 only transiently and became refractory to further stimulation. The exhaustion of cytokine production impacted the T cell polarizing process. Soon after stimulation DCs primed strong TH1 responses, whereas at later time points the same cells preferentially primed TH2 and nonpolarized T cells. These findings indicate that during an immune response, T cell priming conditions may change in the lymph nodes, suggesting another mechanism for the regulation of effector and memory T cells.

Density-dependent induction of TNF-alpha release from human monocytes by immobilized P-selectin

P-selectin purified from human platelets, when immobilized on a solid surface, induced monocytes to release tumor necrosis factor-alpha (TNF-alpha). The induction of TNF-alpha release was dependent on the concentration of P-selectin used for the immobilization, and the maximal stimulation was observed when the plate was coated with 0.3 microgram/ml of P-selectin. Use of either a higher or a lower concentration of P-selectin for the plate-coating was found to elicit less TNF-alpha release, although the higher concentration of P-selectin caused a stronger adhesion of HL-60 leukemic cells. The expression of mRNA for TNF-alpha roughly paralleled the TNF-alpha secretion, as assessed by RT-PCR. These results indicate that monocytes are activated by immobilized P-selectin in a density-dependent manner.