Disparate intracellular processing of human IL-12 preprotein subunits: atypical processing of the P35 signal peptide

The IL-21/IL-21R signaling axis regulates CD4+ T cell responsiveness to IL-12 to promote bacterial-induced colitis

IL-21/IL-21R signaling dysregulation is linked to multiple chronic intestinal inflammatory disorders in humans and animal models of human diseases. In addition to its critical requirement for the generation and development of germinal center B cells, IL-21/IL-21R signaling can also regulate the effector functions of a variety of T cell subsets. The antibody-mediated abrogation of IL-21/IL-21R signaling led to the impaired expression of IFN-γ by mucosal CD4+ T cells from human subjects with colitis, suggesting an IL-21/IL-21R-triggered positive feedback loop of the TH1 immune response in the colon. Despite recent advances in our understanding of the mechanisms underpinning the regulation of pro-inflammatory immune responses by the IL-21/IL-21R signaling axis, it remains unclear how this pathway or its downstream molecules contribute to inflammation during bacterial-induced colitis. This study found that IL-21 enhances the surface expression of IL-12Rβ2, but not IL-12Rβ1, in CD4+ T cells, leading to TH1 differentiation and stability. Consistently, these findings also point to an indispensable role of the IL-12Rβ2 signaling axis in promoting pro-inflammatory immune responses during Citrobacter rodentium-induced colitis. Genetic deletion of the IL-12Rβ2 signaling pathway led to the attenuation of C. rodentium-induced colitis in vivo. The genetic deletion of the IL-12Rβ2 signaling pathway did not alter the host's ability to respond adequately to C. rodentium infection or the ability of Il12rb2-/- mice to express antigen-specific cytokines (IFN-γ, IL-17A). IL-21 is a pleiotropic cytokine exerting a wide range of immunomodulatory functions in multiple tissues, and its direct targeting may result in undesirable off-target consequences. These findings highlight the possibility for targeted manipulations of signaling cascades downstream of main regulators of pro-inflammatory responses to control invading pathogens while preserving the integrity of host immune responses. A better understanding of the novel mechanisms by which IL-21/IL-21R signaling regulates bacterial-induced colitis will provide insights into the development of new therapeutic and preventive strategies to harness IL-21/IL-21R signaling or its downstream molecules to treat infectious colitis.

Assembly-induced folding regulates interleukin 12 biogenesis and secretion

Members of the IL-12 family perform essential functions in immunoregulation by connecting innate and adaptive immunity and are emerging therapeutic targets. They are unique among other interleukins in forming heterodimers that arise from extensive subunit sharing within the family, leading to the production of at least four functionally distinct heterodimers from only five subunits. This raises important questions about how the assembly of IL-12 family members is regulated and controlled in the cell. Here, using cell-biological approaches, we have dissected basic principles that underlie the biogenesis of the founding member of the family, IL-12. Within the native IL-12 heterodimer, composed of IL-12α and IL-12β, IL-12α possesses three intramolecular and one intermolecular disulfide bridges. We show that, in isolation, IL-12α fails to form its native structure but, instead, misfolds, forming incorrect disulfide bonds. Co-expression of its β subunit inhibits misfolding and thus allows secretion of biologically active heterodimeric IL-12. On the basis of these findings, we identified the disulfide bonds in IL-12α that are critical for assembly-induced secretion and biological activity of IL-12 versus misfolding and degradation of IL-12α. Surprisingly, two of the three disulfide bridges in IL-12α are dispensable for IL-12 secretion, stability, and biological activity. Extending our findings, we show that misfolding also occurs for IL-23α, another IL-12 family protein. Our results indicate that assembly-induced folding is key in IL-12 family biogenesis and secretion. The identification of essential disulfide bonds that underlie this process lays the basis for a simplified yet functional IL-12 cytokine.

The SNARE VAMP7 Regulates Exocytic Trafficking of Interleukin-12 in Dendritic Cells

Interleukin-12 (IL-12), produced by dendritic cells in response to activation, is central to pathogen eradication and tumor rejection. The trafficking pathways controlling spatial distribution and intracellular transport of IL-12 vesicles to the cell surface are still unknown. Here, we show that intracellular IL-12 localizes in late endocytic vesicles marked by the SNARE VAMP7. Dendritic cells (DCs) from VAMP7-deficient mice are partially impaired in the multidirectional release of IL-12. Upon encounter with antigen-specific T cells, IL-12-containing vesicles rapidly redistribute at the immune synapse and release IL-12 in a process entirely dependent on VAMP7 expression. Consistently, acquisition of effector functions is reduced in T cells stimulated by VAMP7-null DCs. These results provide insights into IL-12 intracellular trafficking pathways and show that VAMP7-mediated release of IL-12 at the immune synapse is a mechanism to transmit innate signals to T cells.

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Intracellular trafficking of IL-12 in dendritic cells is mediated by the SNARE VAMP7

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VAMP7 is required for optimal secretion of IL-12 in the extracellular space

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IL-12/VAMP7⁺ vesicles gather at the immune synapse

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VAMP7 controls synaptic release of IL-12 and IFN-γ production in T cells

Optimization of canine interleukin-12 production using a baculovirus insect cell expression system

Background

Interleukin-12 is an important cytokine in mediating cellular immune responses.

Results

Recombinant single-chain canine IL-12 was produced in a baculovirus-insect cell system with the aim of conducting further studies on modulation of immune responses in dogs. To optimize the production of recombinant canine IL-12, a classical baculovirus and a modified vector (chitinase A and v-cathepsin knockout) were used containing a native or an optimized insert of canine IL-12. The optimized IL-12 construct contained the GP64 signal peptide and was synthesized with optimized codons for expression in Trichoplusia ni cells. Dot-blot and Western blot analysis showed the highest production levels of recombinant IL-12 protein by the use of the modified baculovirus vector containing the optimized insert, at a multiplicity of infection of five and at 48 h after infection. The recombinant cytokine was successfully purified and showed a good degree of purity, integrity, folding, and yield, with very little endotoxin contamination. Recombinant canine IL-12 induced IFN-γ in canine lymphocytes, indicating that it was biologically active.

Conclusion

Therefore, this study describes an efficient method to produce adequate amounts of biologically active canine IL-12, useful for immunomodulation studies in dogs.

Reciprocal Regulation of Substance P and IL-12/IL-23 and the Associated Cytokines, IFNγ/IL-17: A Perspective on the Relevance of This Interaction to Multiple Sclerosis

The neuropeptide substance P (SP) exhibits cytokine-like properties and exerts different effects in autoimmune inflammation. Various immune cells express SP and its neurokinin-1 receptor (NK1R) isoforms. A role for SP has been demonstrated in a number of autoimmune conditions, including multiple sclerosis (MS). In this work, we studied the role of SP and NK1R in human immune cells with a focus on their relationship with IL-12/IL-23 family cytokines and the associated IFN-γ/IL-17. AIMS: (1) To determine the role of SP mediated effects on induction of various inflammatory cytokines in peripheral blood mononuclear cells (PBMC); (2) to investigate the expression of SP and its receptor in T cells and the effects of stimulation with IL-12 and IL-23. Quantitative real-time PCR, flow cytometry, ELISA, promoter studies on PBMC and primary T cells from healthy volunteers, and Jurkat cell line. Treatment with SP significantly increased the expression of IL-12/IL-23 subunit p40, IL-23 p19 and IL-12 p35 mRNA in human PBMC. Expression of NK1R and SP in T cells was upregulated by IL-23 but a trend was observed with IL-12. The IL-23 effect likely involves IL-17 production that additionally mediates IL-23 effects. Mutual interactions exist with SP enhancing the cytokines IL-23 and IL-12, and SP and NK1R expression being differentially but potentially synergistically regulated by these cytokines. These findings suggest a proinflammatory role for SP in autoimmune inflammation. We propose a model whereby immunocyte derived SP stimulates Th1 and Th17 autoreactive cells migrating to the central nervous system (CNS), enhances their crossing the blood brain barrier and perpetuates inflammation in the CNS by being released from damaged nerves and activating both resident glia and infiltrating immune cells. SP may be a therapeutic target in MS.

Cytokine Secretion in Macrophages: SNAREs, Rabs, and Membrane Trafficking

Macrophages have the capacity to rapidly secrete a wide range of inflammatory mediators that influence the development and extent of an inflammatory response. Newly synthesized and/or preformed stored cytokines and other inflammatory mediators are released upon stimulation, the timing, and volume of which is highly regulated. To finely tune this process, secretion is regulated at many levels; at the level of transcription and translation and post-translationally at the endoplasmic reticulum (ER), Golgi, and at or near the cell surface. Here, we discuss recent advances in deciphering these cytokine pathways in macrophages, focusing on recent discoveries regarding the cellular machinery and mechanisms implicated in the synthesis, trafficking, and secretion of cytokines. The specific roles of trafficking machinery including chaperones, GTPases, cytoskeletal proteins, and SNARE membrane fusion proteins will be discussed.

Efficient production and purification of recombinant human interleukin-12 (IL-12) overexpressed in mammalian cells without affinity tag

Interleukin-12 is a heterodimeric, pro-inflammatory cytokine that is a key driver of cell-mediated immunity. Clinical interest in IL-12 is significant due to its potent anti-tumor activity and efficacy in controlling certain infectious diseases such as Leishmaniasis and Listeria infection. For clinical applications, the ease of production and purification of IL-12 and the associated cost continues to be a consideration. In this context, we report a simple and effective heparin-affinity based purification of recombinant human IL-12 (hIL-12) from the serum-free supernatants of stable IL-12-transduced HEK293 cells. Fractionation of culture supernatants on heparin Sepharose columns revealed that hIL-12 elutes as a single peak in 500 mM NaCl. Coomassie staining and Western blot analysis showed that hIL-12 eluted in 500 mM NaCl is homogeneous. Purity of hIL-12 was ascertained by RP-HPLC and ESI-MS analysis, and found to be ∼98%. Western blot analysis, using monoclonal antibodies, demonstrated that the crucial inter-subunit disulfide bond linking the p35 and p40 subunits is intact in the purified hIL-12. Results of far UV circular dichroism, steady-state tryptophan fluorescence, and differential scanning calorimetry experiments suggest that purified hIL-12 is in its stable native conformation. Enzyme linked immunosorbent assays (ELISAs) and bioactivity studies demonstrate that hIL-12 is obtained in high yields (0.31±0.05 mg/mL of the culture medium) and is also fully bioactive. Isothermal titration calorimetry data show that IL-12 exhibits a moderate binding affinity (Kd(app)=69±1 μM) to heparin. The purification method described in this study is expected to provide greater impetus for research on the role of heparin in the regulation of the function of IL-12. In addition, the results of this study provide an avenue to obtain high amounts of IL-12 required for structural studies which are aimed at the development of novel IL-12-based therapeutics.

The p40 subunit of interleukin (IL)-12 promotes stabilization and export of the p35 subunit: implications for improved IL-12 cytokine production

IL-12 is a 70-kDa heterodimeric cytokine composed of the p35 and p40 subunits. To maximize cytokine production from plasmid DNA, molecular steps controlling IL-12p70 biosynthesis at the posttranscriptional and posttranslational levels were investigated. We show that the combination of RNA/codon-optimized gene sequences and fine-tuning of the relative expression levels of the two subunits within a cell resulted in increased production of the IL-12p70 heterodimer. We found that the p40 subunit plays a critical role in enhancing the stability, intracellular trafficking, and export of the p35 subunit. This posttranslational regulation mediated by the p40 subunit is conserved in mammals. Based on these findings, dual gene expression vectors were generated, producing an optimal ratio of the two subunits, resulting in a ∼1 log increase in human, rhesus, and murine IL-12p70 production compared with vectors expressing the wild type sequences. Such optimized DNA plasmids also produced significantly higher levels of systemic bioactive IL-12 upon in vivo DNA delivery in mice compared with plasmids expressing the wild type sequences. A single therapeutic injection of an optimized murine IL-12 DNA plasmid showed significantly more potent control of tumor development in the B16 melanoma cancer model in mice. Therefore, the improved IL-12p70 DNA vectors have promising potential for in vivo use as molecular vaccine adjuvants and in cancer immunotherapy.

Cytokine profiles affecting the pathogenesis of autoimmune hepatitis in Japanese patients

AIM

  Autoimmune hepatitis (AIH) is a chronic hepatitis of unknown etiology, although several cytokines have been implicated in its pathogenesis and severity. This study investigated the relationship between circulating cytokines in the pretreatment phase and remission following corticosteroid therapy phase in Japanese AIH patients.

METHODS

  A total of 28 cytokines were measured simultaneously by multiple bead array technology in the sera of 40 patients with AIH collected during pretreatment and remission phases.

RESULTS

  Interleukin (IL)-12p40, interferon-γ-inducible protein (IP-10), macrophage inflammatory protein (MIP)-1α, MIP-1β, IL-17F and IL-18 were significantly decreased during remission from pretreatment stage levels. The level of IP-10 in the pretreatment phase was correlated with serum levels of alanine aminotransferase.

CONCLUSION

  Our results suggest that a complex interplay of several cytokines, especially pro-inflammatory and T-helper 17 cytokines and regulatory T-cell suppression by IL-12p40 may play a pivotal role in the pathogenesis of AIH.

Mechanisms of cytokine secretion: a portfolio of distinct pathways allows flexibility in cytokine activity

Since cytokines are potent immunoregulators that can determine the fate of an immune response, their expression is tightly regulated at the transcriptional level. Recent research, however, has also revealed complex post-translational mechanisms through which cytokine secretion, and thereby cytokine activity, is regulated. Here, we review the progress in our understanding of the portfolio of pathways that regulate cytokine intracellular storage, transport, and release. Like other secreted proteins, cytokines utilize canonical and non-canonical secretory pathways for extracellular release. Illustrated by IL-1β, IL-2, TNF-α, IL-12 and IL-15 secretion as selected examples, we discuss common and alternative cytokine secretion pathways and relate them to the consequences these distinct pathways have for cytokine function, mode of action and stability.

Semliki Forest virus-mediated gene therapy of the RG2 rat glioma

AIMS

Glioblastoma multiforme is the most common and most malignant adult brain tumour. Despite numerous advances in cancer therapy there has been little change in the prognosis of glioblastoma multiforme, which remains invariably fatal. We examined the Semliki Forest virus virus-like particle (SFV VLP) expression system encoding interleukin-12 (IL-12) as a therapeutic intervention against the syngeneic RG2 rat glioma model.

METHODS

Glioma-bearing rats were treated with IL-12-encoding SFV VLPs via an implanted cannula. Animals were treated with 5 × 10⁷ (low-dose) or 5 × 10⁸ (high-dose) VLPs per treatment and the effect on glioma growth and survival was assessed.

RESULTS

Low-dose treatment produced a 70% reduction in tumour volume, associated with a significant extension (20.45%) in survival that was dependent upon IL-12 expression. High-dose treatment resulted in an 87% reduction in tumour volume, related to the oncolytic capacity of the SFV VLP system. VLP delivery to the central nervous system (CNS) demonstrated the potential of the vector system to induce lethal pathology that was unrelated to replication-competent virus or high-level IL-12 expression. Treatment-related death was pronounced in high dose-treated animals and appeared to be the result of inflammation, necrosis and oedema at the inoculation site.

CONCLUSION

The efficacy of an IL-12 gene therapy approach for the treatment of the RG2 glioma model has been demonstrated in addition to the oncolytic capacity of the VLP vector system. Despite this, the broad tropism of the SFV-based expression vector may limit use as a CNS gene therapy vector unless this inherent limitation can be overcome.

Endoplasmic reticulum stress-induced transcription factor, CHOP, is crucial for dendritic cell IL-23 expression

The endoplasmic reticulum (ER) stress response detects malfunctions in cellular physiology, and microbial pattern recognition receptors recognize external threats posed by infectious agents. This study has investigated whether proinflammatory cytokine expression by monocyte-derived dendritic cells is affected by the induction of ER stress. Activation of ER stress, in combination with Toll-like receptor (TLR) agonists, markedly enhanced expression of mRNA of the unique p19 subunit of IL-23, and also significantly augmented secretion of IL-23 protein. These effects were not seen for IL-12 secretion. The IL-23 gene was found to be a target of the ER stress-induced transcription factor C/EBP homologous protein (CHOP), which exhibited enhanced binding in the context of both ER stress and TLR stimulation. Knockdown of CHOP in U937 cells significantly reduced the synergistic effects of TLR and ER stress on IL-23p19 expression, but did not affect expression of other LPS-responsive genes. The integration of ER stress signals and the requirement for CHOP in the induction of IL-23 responses was also investigated in a physiological setting: infection of myeloid cells with Chlamydia trachomatis resulted in the expression of CHOP mRNA and induced the binding of CHOP to the IL-23 promoter. Furthermore, knockdown of CHOP significantly reduced the expression of IL-23 in response to this intracellular bacterium. Therefore, the effects of pathogens and other environmental factors on ER stress can profoundly affect the nature of innate and adaptive immune responses.

A multiscale systems perspective on cancer, immunotherapy, and Interleukin-12

Monoclonal antibodies represent some of the most promising molecular targeted immunotherapies. However, understanding mechanisms by which tumors evade elimination by the immune system of the host presents a significant challenge for developing effective cancer immunotherapies. The interaction of cancer cells with the host is a complex process that is distributed across a variety of time and length scales. The time scales range from the dynamics of protein refolding (i.e., microseconds) to the dynamics of disease progression (i.e., years). The length scales span the farthest reaches of the human body (i.e., meters) down to the range of molecular interactions (i.e., nanometers). Limited ranges of time and length scales are used experimentally to observe and quantify changes in physiology due to cancer. Translating knowledge obtained from the limited scales observed experimentally to predict patient response is an essential prerequisite for the rational design of cancer immunotherapies that improve clinical outcomes. In studying multiscale systems, engineers use systems analysis and design to identify important components in a complex system and to test conceptual understanding of the integrated system behavior using simulation. The objective of this review is to summarize interactions between the tumor and cell-mediated immunity from a multiscale perspective. Interleukin-12 and its role in coordinating antibody-dependent cell-mediated cytotoxicity is used illustrate the different time and length scale that underpin cancer immunoediting. An underlying theme in this review is the potential role that simulation can play in translating knowledge across scales.

Regulation of interleukin-12/interleukin-23 production and the T-helper 17 response in humans

Interleukin-12 (IL-12) and IL-23 share a common chain. Yet, their production in response to pathogens is differentially regulated, and their functions are distinct and often antithetic. IL-12 is involved in the induction or amplification of the T-helper (Th) type 1 response, whereas IL-23 has been associated with the generation of the Th17 response and IL-17 production. Mycobacterium tuberculosis and yeast zymosan induce IL-23, but in the absence of other stimuli, no IL-12 is induced in human dendritic cells (DCs). The stimulation of IL-23 by M. tuberculosis was mostly explained by the triggering of Toll-like receptor (TLR2) and the cytoplasmic receptor nucleotide oligomerization domain (NOD)-containing protein 2, whereas zymosan induces IL-23 primarily by stimulating the beta-glucan receptor dectin-1 alone or in combination with TLR2. IL-23, IL-6, transforming growth factor (TGF-beta1), and IL-1beta in supernatants from activated human DCs induce human naive CD4(+) T cells to produce IL-17. These data are consistent with various recent reports that TGF-beta is an inducer of IL-17 production both in human and in mouse cells. However, IL-1 is necessary in combination with some or all of the other cytokines to induce IL-17 production in human T cells. The ability of various stimuli to induce Th17 cells depends not only on their induction of IL-23, IL-6, and TGF-beta production in DCs but also on their ability to activate directly or indirectly the inflammasome and to induce IL-1beta.

How a cytokine is chaperoned through the secretory pathway by complexing with its own receptor: lessons from interleukin-15 (IL-15)/IL-15 receptor alpha

While it is well appreciated that receptors for secreted cytokines transmit ligand-induced signals, little is known about additional roles for cytokine receptor components in the control of ligand transport and secretion. Here, we show that interleukin-15 (IL-15) translocation into the endoplasmic reticulum occurs independently of the presence of IL-15 receptor alpha (IL-15R alpha). Subsequently, however, IL-15 is transported through the Golgi apparatus only in association with IL-15R alpha and then is secreted. This intracellular IL-15/IL-15R alpha complex already is formed in the endoplasmic reticulum and, thus, enables the further trafficking of complexed IL-15 through the secretory pathway. Just transfecting IL-15R alpha in cells, which transcribe but normally do not secrete IL-15, suffices to induce IL-15 secretion. Thus, we provide the first evidence of how a cytokine is chaperoned through the secretory pathway by complexing with its own high-affinity receptor and show that IL-15/IL-15R alpha offers an excellent model system for the further exploration of this novel mechanism for the control of cytokine secretion.

Differential regulation of interleukin 12 and interleukin 23 production in human dendritic cells

We analyzed interleukin (IL) 12 and IL-23 production by monocyte-derived dendritic cells (mono-DCs). Mycobacterium tuberculosis H37Rv and zymosan preferentially induced IL-23. IL-23 but not IL-12 was efficiently induced by the combination of nucleotide-binding oligodimerization domain and Toll-like receptor (TLR) 2 ligands, which mimics activation by M. tuberculosis, or by the human dectin-1 ligand β-glucan alone or in combination with TLR2 ligands, mimicking induction by zymosan. TLR2 ligands inhibited IL-12 and increased IL-23 production. DC priming with interferon (IFN) γ strongly increased IL-12 production, but was not required for IL-23 production and inhibited IL-23 production induced by β-glucan. The pattern of IL-12 and IL-23 induction was reflected in accumulation of the IL-12p35 and IL-23p19 transcripts, respectively, but not IL-12/23p40. Although IL-23, transforming growth factor β, and IL-6 contained in the supernatants of activated mono-DCs played a role in the induction of IL-17 by human CD4⁺ T cells, IL-1β, in combination with one or more of those factors, was required for IL-17 production, and its production determined the differential ability of the stimuli used to elicit mono-DCs to produce soluble factors directing IL-17 production. Thus, the differential ability of pathogens to induce antigen-presenting cells to produce cytokines regulates the immune response to infection.

Cloning and characterization of an adenoviral vector for highly efficient and doxycycline-suppressible expression of bioactive human single-chain interleukin 12 in colon cancer

BACKGROUND

Interleukin-12 (IL-12) is well characterized to induce cellular antitumoral immunity by activation of NK-cells and T-lymphocytes. However, systemic administration of recombinant human IL-12 resulted in severe toxicity without perceptible therapeutic benefit. Even though intratumoral expression of IL-12 leads to tumor regression and long-term survival in a variety of animal models, clinical trials have not yet shown a significant therapeutic benefit. One major obstacle in the treatment with IL-12 is to overcome the relatively low expression of the therapeutic gene without compromising the safety of such an approach. Our objective was to generate an adenoviral vector system enabling the regulated expression of very high levels of bioactive, human IL-12.

RESULTS

High gene expression was obtained utilizing the VP16 herpes simplex transactivator. Strong regulation of gene expression was realized by fusion of the VP16 to a tetracycline repressor with binding of the fusion protein to a flanking tetracycline operator and further enhanced by auto-regulated expression of its fusion gene within a bicistronic promoter construct. Infection of human colon cancer cells (HT29) at a multiplicity of infection (m.o.i.) of 10 resulted in the production of up to 8000 ng/106 cells in 48 h, thus exceeding any published vector system so far. Doxycycline concentrations as low as 30 ng/ml resulted in up to 5000-fold suppression, enabling significant reduction of gene expression in a possible clinical setting. Bioactivity of the human single-chain IL-12 was similar to purified human heterodimeric IL-12. Frozen sections of human colon cancer showed high expression of the coxsackie adenovirus receptor with significant production of human single chain IL-12 in colon cancer biopsies after infection with 3*107 p.f.u. Ad.3r-scIL12. Doxycycline mediated suppression of gene expression was up to 9000-fold in the infected colon cancer tissue.

CONCLUSION

VP16 transactivator-mediated and doxycycline-regulated expression of the human interleukin-12 gene enables highly efficient and tightly controlled cytokine expression in human cancer. These data illustrate the potential of the described adenoviral vector system for the safe and superior expression of therapeutic genes in the treatment of colorectal cancer and other malignancies.

A Multi-Scale Model of Dendritic Cell Education and Trafficking in the Lung: Implications for T Cell Polarization

Health Sciences face a significant challenge in translating basic science data into improved understanding of innate and adaptive immunity. To improve understanding of the dynamic role of dendritic cells in the lung, a mathematical model was developed using a physiologically structured framework that explicitly accounts for functional heterogeneity. As sentinels of the immune system, dendritic cells play critical roles in coupling innate to adaptive immunity and produce an important immune regulatory cytokine: IL-12. The term IL-12 actually refers to the net bioactivity of three related proteins; IL12p40, IL12p70, and IL12(p40)2; assembled from two independent gene products: p35 and p40. The model for dendritic cell education and trafficking was created by incorporating five dimensions: chronological time, maturational age, p35 signal, p40 signal, and spatial location. The computational framework was calibrated to and validated against appropriate experimental studies. Using this validated model, I explore the impact of dynamic changes in the lung epithelium of IL-4, IFN-gamma, and PGE2 on the dynamic ability of dendritic cells to polarize T cell subsets. In summary, this multi-scale model provides an essential aid in understanding the impact of a dynamically changing lung microenvironment on the ability of dendritic cells to orchestrate adaptive immunity.

Regulation of lipopolysaccharide-induced interleukin-12 production by activation of repressor element GA-12 through hyperactivation of the ERK pathway

Interleukin-12 (IL-12) functions as a representative lipopolysaccharide (LPS) mediator in both innate and adaptive immunity. We investigated the regulation of LPS-induced IL-12 production by mouse macrophages. In response to LPS, peritoneal macrophages produced bioactive IL-12 p70, a heterodimer (p40/p35) of subunits, but macrophage lines such as J774.1 and RAW264.7 did not. Induction of the p35 subunit was impaired in both cell lines, and additional impairment of p40 induction was observed in RAW264.7 cells. These results suggest that some negative regulatory mechanisms against LPS-induced IL-12 p40 production are constitutively functioning in RAW264.7 cells but not in the other types of cells. Activation of GA-12 (a repressor element of IL-12 p40), rather than suppression of promoter elements, such as binding sites for NF-kappaB, AP-1, and IRF-1, was detected in LPS-stimulated RAW264.7 cells, accompanying hyperactivation of extracellular signal-related kinase (ERK). When ERK activation was suppressed by an inhibitor (U0126), production of p40 rose from an undetectable to a substantial level and GA-12 activation decreased. In peritoneal macrophages, stimulation with a high dose of LPS reduced p40 production with enhanced activation of ERK. Pretreatment of the cells with phorbol myristate acetate to enhance ERK activation reduced p40 production in response to the optimal LPS stimulation. Taken together, these results demonstrate that hyperactivation of the ERK pathway plays a role in upstream signaling for the activation of GA-12, leading to the repression of IL-12 p40 production in mouse macrophages.

Expression of functional interleukin-12 from mouse in transgenic tomato plants

Transgenic plants have been employed successfully as a low-cost system for the production of therapeutically valuable proteins, including antibodies, antigens and hormones. Here, we report the expression of a cytokine with immunomodulatory function, mouse interleukin-12 (IL-12), in transgenic tomato plants. Single-chain mouse IL-12 driven by the CaMV 35S promoter, accumulates to high levels in leaves and fruits (up to 7.3 and 3.4 microg per gram of fresh weight, respectively). Mouse IL-12 expressed in tomato displays biological activity in vitro, as determined by interferon-gamma (IFN-gamma) secretion by T cells. Possible uses of this plant-based cytokine involving mucosal delivery are discussed.

The ratio of P40 monomer to dimer is an important determinant of IL-12 bioactivity

IL-12 is a 75 kDa heterodimer (IL12p70) comprised of independently regulated disulfide-linked 40 kDa (p40) and 35 kDa (p35) subunits. The p40 subunit exists extracellularly as a monomer (IL12p40) or dimer (IL12(p40)2) and can antagonize the action of IL12p70. Given the disagreement in the literature over the physiologic roles for IL12p70, IL12p40, and IL12(p40)2, we asked whether the bioactivity of IL-12 depended only on the concentration of the IL12p70 subunit alone or whether the relative concentrations of IL12p70, IL12p40, and IL12(p40)2 and their competitive binding with the IL-12 receptor are essential for determining IL-12 bioactivity under simulated human physiologic conditions. A mathematical model for IL-12 bioactivity was created by incorporating the production of IL12p70, IL12p40, and IL12(p40)2 by mature human DC and the interaction of these species with the IL-12 receptor. Using this model, we explored the effects of IFN-gamma, IL-4, and PGE2 concentrations on the bioactivity of IL-12. The simulations suggest that the concentration of IL12p70 alone is not indicative of IL-12 bioactivity; rather, the bioactivity of IL-12 produced by mature DC depends on IL12p70, IL12p40, and IL12(p40)2 production and their competitive interaction with the IL-12 receptor. In addition to the typically measured quantities of total p40 (IL12p40 + IL12(p40)2) and IL12p70, the ratio of IL12p40 to IL12(p40)2 is an equally important, yet underreported, determinant of IL-12 bioactivity.

A new vector for controllable expression of an anti-HER2/neu mini-antibody-barnase fusion protein in HEK 293T cells

Tumor-targeted vectors with controllable expression of therapeutic genes and specific antitumor antibodies are promising tools for the reduction of malignant tumors. Here we describe a new plasmid for the eukaryotic expression of an anti-HER2/neu mini-antibody-barnase fusion protein (4D5 scFv-barnase-His(5)) with an NH(2)-terminal leader peptide. The 4D5 scFv-barnase-His(5) gene was placed downstream of the tetracycline responsive-element minimal promoter in the vector using the Tet-Off gene-expression system. The Bacillus amyloliquefaciens ribonuclease barnase is toxic for the host cells. To overcome this problem, barstar gene under its own minimal cytomegalovirus promoter was used in designed vector. Barstar inhibits the background level of barnase in the cells in the presence of tetracycline in culture medium. The HEK 293T cells were transfected with the designed vector, and the 4D5 scFv-barnase-His(5) fusion protein was identified by anti-barnase antibodies in cell culture medium and after purification from cell lysates using metal-affinity chromatography. The overexpression of the anti-HER2/neu mini-antibody-barnase fusion protein decreased the intensity of fluorescence of HEK 293T cells co-transfected with the generated plasmid and a plasmid containing the gene of enhanced green fluorescent protein (pEGFP-N1), in comparison with the intensity of fluorescence of HEK 293T cells transfected with pEGFP-N1, in the absence of tetracycline in the medium. The effect of the 4D5 scFv-barnase-His(5) on EGFP fluorescence indicates that the introduced barnase functions as a ribonuclease inside the cells. The anti-HER2/neu mini-antibody could be used to deliver barnase to HER2/neu-positive cells and provide its penetration into the target cells, as HER2/neu is a ligand-internalizing receptor. This expression vector has potential applications to both gene and antibody therapies of cancer.

Synergistic Activation of Interleukin-12 p35 Gene Transcription by Interferon Regulatory Factor-1 and Interferon Consensus Sequence-binding Protein

Interferon regulatory factor-1 (IRF-1) and interferon consensus sequence-binding protein (ICSBP or IRF-8) are two members of the IRF family of transcription factors that play critical roles in interferon signaling in a wide range of host responses to infection and malignancy. Interleukin-12 (IL-12) is a key factor in the induction of innate resistance and generation of T helper type 1 cells and cytotoxic T lymphocytes. In this work, we find that ICSBP-deficient macrophages are highly defective in the production of IL-12. The defect is also observed at the level of IL-12 p40 and p35 mRNA expression. Transcriptional analyses revealed that ICSBP is a potent activator of the IL-12 p35 gene. It acts through a site localized to -226 to -219, named ICSBP-response element (ICSBP-RE), in the human IL-12 p35 promoter through physical association with IRF-1 both in vitro and in vivo. Co-expression of ICSBP and IRF-1 synergistically stimulates the IL-12 p35 promoter activity. Mutations at the ICSBP-RE results in the loss of protein binding as well as transcriptional activation by ICSBP alone or together with IRF-1. This study provides novel mechanistic information on how signals initiated during innate and adaptive immune responses synergize to yield greater IL-12 production and sustained cellular immunity.

Expression of a single-chain human interleukin-12 gene in transgenic tobacco plants and functional studies

Interleukin 12 (IL-12) is a key heterodimeric cytokine produced by a variety of antigen-presenting cells, including dendritic cells, macrophages, and B cells. It displays a potent array of biological activities affecting natural killer (NK) and T cells. These activities include promotion of cell-mediated or type 1 T helper cell responses (Th1). Due to that property, IL-12 has been employed in cancer immunotherapy, in mouse models of infectious diseases and in airway inflammation, and it may also have utility as a vaccine adjuvant. Transgenic plants are being used in many laboratories around the world for the production of therapeutically valuable proteins and as vehicles for oral vaccines. Here we present the expression of a single-chain human interleukin-12 in transgenic tobacco plants. The biological activity of plant-produced IL-12 was determined by interferon gamma (IFN-gamma) production by natural killer (NK) cells, and the level of production was comparable to that obtained with commercially available recombinant IL-12. The potential use of this recombinant protein is discussed.

Timing of IFN-beta exposure during human dendritic cell maturation and naive Th cell stimulation has contrasting effects on Th1 subset generation: a role for IFN-beta-mediated regulation of IL-12 family cytokines and IL-18 in naive Th cell differentiation

Type I IFNs, IFN-alpha and IFN-beta, are early effectors of innate immune responses against microbes that can also regulate subsequent adaptive immunity by promoting antimicrobial Th1-type responses. In contrast, the ability of IFN-beta to inhibit autoimmune Th1 responses is thought to account for some of the beneficial effects of IFN-beta therapy in the treatment of relapsing remitting multiple sclerosis. To understand the basis of the paradoxical effects of IFN-beta on the expression of Th1-type immune responses, we developed an in vitro model of monocyte-derived dendritic cell (DC)-dependent, human naive Th cell differentiation, in which one can observe both positive and negative effects of IFN-beta on the generation of Th1 cells. In this model we found that the timing of IFN-beta exposure determines whether IFN-beta will have a positive or a negative effect on naive Th cell differentiation into Th1 cells. Specifically, the presence of IFN-beta during TNF-alpha-induced DC maturation strongly augments the capacity of DC to promote the generation of IFN-gamma-secreting Th1 cells. In contrast, exposure to IFN-beta during mature DC-mediated primary stimulation of naive Th cells has the opposite effect, in that it inhibits Th1 cell polarization and promotes the generation of an IL-10-secreting T cell subset. Studies with blocking mAbs and recombinant cytokines indicate that the mechanism by which IFN-beta mediates these contrasting effects on Th1 cell generation is at least in part by differentially regulating DC expression of IL-12 family cytokines (IL-12 and/or IL-23, and IL-27) and IL-18.

The power of combinatorial immunology: IL-12 and IL-12-related dimeric cytokines in infectious diseases

Appropriate induction of a Th1 immune response is required for effective antimicrobial immunity. However, dysregulated Th1 immune responses after infection may also lead to immunopathology. Thus, cell-mediated immune responses have to be tightly regulated. Upon infection, the production of interleukin (IL)-12, a heterodimeric cytokine composed of a p35 and a p40 subunit, is the dominant factor in Th1 cell development. The recent discovery of novel dimeric cytokines closely related to IL-12 add now to our understanding of cellular immunity and the fine tuning of T cell responses. At the onset of infection, IL-27, a heterodimer composed of the IL-12p40-related protein EBI-3 (Epstein-Barr virus-induced gene 3) and the IL-12p35-related protein p28 induces the expression of a functional IL-12 receptor in naive CD4+ T cells, making these cells sensitive to IL-12-mediated Th cell development. Later during infection, IL-23, a heterodimer composed of the IL-12p40 subunit and the IL-12p35-related molecule p19, preferentially acts on Th1 effector/memory CD4+ T cells. The IL-12p40 subunit can also form a homodimer, IL-12p80, which act as an IL-12 and IL-23 antagonist by competing at their receptors. This review focuses on these IL-12-related cytokines contributing to fine tuning of T cell responses after infection with intracellular pathogens.

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.

Differential regulation of interleukin-12 p40 and p35 induction via Erk mitogen-activated protein kinase-dependent and -independent mechanisms and the implications for bioactive IL-12 and IL-23 responses

Bioactive interleukin (IL)-12 is a 70 000-molecular weight (MW) heterodimeric cytokine comprising p40 and p35 chains. However, p40 can also form homodimers that antagonize bioactive IL-12 or heterodimerize with p19 to form IL-23, which exhibits overlapping yet distinct functions to that of IL-12. We now define distinct signalling mechanisms that regulate lipopolysaccharide (LPS)-mediated induction of IL-12 p40 and p35 in macrophages and which may therefore provide therapeutic targets for precise and specific fine-tuning of cytokine responses. Thus, whilst LPS-induced p38 mitogen-activated protein kinase (MAPkinase) activation is required for the induction of both p40 and p35 subunits, Erk MAPkinase signalling mediates negative feedback regulation of p40, but not p35, production. Such Erk MAPkinase activation is downstream of calcium influx and targets LPS-induced IL-12 p40 transcription by suppressing the synthesis of the transcription factor, interferon regulatory factor-1 (IRF-1). In contrast, negative regulation of the p35 subunit of IL-12 occurs via a calcium-dependent, but Erk-independent, mechanism, which is likely to involve nuclear factor (NF)-kappa B signalling. Finally, the importance of both Erk and p38 MAPkinases in differentially regulating IL-12 p40 and p35 production is underscored by each being targeted by ES-62, a product secreted by parasitic filarial nematodes to polarize the immune system towards an anti-inflammatory phenotype conducive to their survival.

Highly suppressible expression of single-chain interleukin-12 by doxycycline following adenoviral infection with a single-vector Tet-regulatory system

BACKGROUND

Adenoviral vectors have been shown to efficiently transfer DNA into a wide variety of eukaryotic cells in vitro and in vivo. However, the therapeutic benefit of this approach is limited by severe side effects as a result of uncontrolled transgene expression.

METHODS

A bi-directional promoter that controls the desired transgene as well as a tetracycline-suppressible transactivator (tTA) was cloned into the E1-region of E1-deleted recombinant adenoviral vectors. Autoregulation within this construct was obtained by tTA expression under control of the operator, to which tTA binds in the absence of tetracycline. Consequently, binding of tetracycline to tTA results in downregulation of tTA as well as the co-expressed transgene in the infected cell.

RESULTS

We were able to suppress luciferase-reporter gene expression by up to 16 000-fold in the presence of doxycycline (dox, 2 micro g/ml). Under control of this tetracycline-regulated system, single-chain interleukin-12 (scIL12) was expressed. Adenovirally mediated expression of this potentially lethal cytokine with strong activation of antitumoral immune response was downregulated by up to 6000-fold in the presence of dox. Subsequently, this downregulation also resulted in a highly significant reduction of interferon-gamma secretion by stimulated splenocytes. These mainly contribute to the toxicity of this immunotherapeutic approach.

CONCLUSIONS

With expression levels exceeding those of the cytomegalovirus (CMV) promoter in almost all cell lines tested, these new vectors will also contribute to the safety of adenoviral approaches by controlled expression without compromising on maximum expression levels.

Interleukin-12 and the regulation of innate resistance and adaptive immunity

Interleukin-12 (IL-12) is a heterodimeric pro-inflammatory cytokine that induces the production of interferon-gamma (IFN-gamma), favours the differentiation of T helper 1 (T(H)1) cells and forms a link between innate resistance and adaptive immunity. Dendritic cells (DCs) and phagocytes produce IL-12 in response to pathogens during infection. Production of IL-12 is dependent on differential mechanisms of regulation of expression of the genes encoding IL-12, patterns of Toll-like receptor (TLR) expression and cross-regulation between the different DC subsets, involving cytokines such as IL-10 and type I IFN. Recent data, however, argue against an absolute requirement for IL-12 for T(H)1 responses. Our understanding of the relative roles of IL-12 and other factors in T(H)1-type maturation of both CD4+ and CD8+ T cells is discussed here, including the participation in this process of IL-23 and IL-27, two recently discovered members of the new family of heterodimeric cytokines.

IL-12: the role of p40 versus p75

Interleukin (IL)-12p75 is a heterodimeric cytokine composed of the product of two different genes that specify p35 and p40 subunits. The prevailing view is that IL-12 acts as a proinflammatory cytokine that bridges the innate and adaptive immune responses and skews T-cell reactivity toward a TH1 cytokine pattern. Though the terms IL-12 and IL-12p40 are often used interchangeably, and measurements of the p40 chain are often interpreted as measurements of the intact p75 heterodimer, such interchangeable usage may be incorrect. In the following discussion, I will delineate an alternative hypothesis for the roles of the p40 and p75 proteins, suggesting specifically, that: (1) in vivo, secretion of free p40 precedes that of p75 in response to pathogens; (2) induction of p40 is a T-independent response by antigen presenting cells (APCs) to early host-pathogen interactions; and (3) IL-12p75 is a late product, whose induction requires T-dependent signals. It is made as a result, rather than as a cause, of TH1 differentiation. Thus, it is the p40 protein, either alone or paired with other polypeptides, rather than p75, that acts as an interface between the innate and adaptive immune responses.

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.

Thiol antioxidants inhibit the formation of the interleukin-12 heterodimer: a novel mechanism for the inhibition of IL-12 production

IL-12 is a 75 kDa heterodimeric cytokine composed of two disulfide-linked subunits, p35 and p40, which plays an important role in the regulation of the immune response. We tested the hypothesis that thiol antioxidants might interfere with dimerization of the two IL-12 subunits. We thus studied the effect of reduced glutathione (GSH) and N-acetyl-cysteine (NAC) on IL-12 p75 production by human THP-1 cell stimulated with IFN-gamma and Staphylococcus aureus Cowan strain I (SAC), using ELISAs specific for IL-12 p75 or the p40 subunit. NAC and GSH, but not cystine, at concentrations of 5-10 mM inhibited production of IL-12 p75 but not of the p40 subunit. NAC did not inhibit p40 or p35 mRNA expression in dendritic cells or THP-1 cells, or NF-kappa B activation in THP-1 cells. The effect of NAC was specific for IL-12 p75, as NAC did not affect induction of MHC class II expression by IFN-gamma-stimulated THP-1 cells. IL-12 dimer formation appears to be reduced by NAC also in vivo, because pretreatment with NAC (1 g/kg, orally), before LPS injection in mice, inhibited peak IL-12 p75 serum levels without affecting those of p40. We conclude that thiol levels regulate IL-12 p75 production and that assembly of the heterodimer is a step that might represent a target for pharmacological intervention.

Deletional analysis of the murine IL-12 p35 promoter comparing IFN-gamma and lipopolysaccharide stimulation

IL-12, pivotal to the development of Th1 cells and formed by association of p35 and p40 subunits, is made by macrophages and the macrophage cell line RAW264.7. In this study, the promoter for p35 was cloned and analyzed. The murine IL-12 p35 gene has promoters upstream from each of the first two exons. The exon 1 and exon 2 promoters, cloned into a reporter vector, were responsive to LPS or IFN-gamma/CD40 ligation in transfected RAW264.7 cells. The exon 2 promoter containing bp -809 to +1 has significant homology to the human p35 promoter. Thus, deletion analysis was performed to determine the regions required for responsiveness to LPS, CD40, and/or IFN-gamma. Base pairs -809 to -740 influenced responsiveness to LPS. In contrast, bp -740to -444 and bp -122 to -100 were required for responses to IFN-gamma, IFN-gamma/LPS, or IFN-gamma/CD40 ligation. Removal of bp -444 to -392 increased the response of the exon 2 promoter to each stimulant. IFN regulatory factor (IRF)-1 is involved in the activity of this promoter at bp -108 to -103 because levels of nuclear IRF-1 correlated with exon 2 promoter activity in response to IFN-gamma and IRF-1 overexpression stimulated and enhanced exon 2 promoter activity. Also, site or deletion mutation of the IRF-1 element at bp -108 to -103 reduced the responsiveness of the promoter and IRF-1 bound to an oligonucleotide containing bp -108 to -103. The data suggest that the response of the p35 promoter to IFN-gamma requires a distinct IRF-1 positive regulatory element at bp -108 to -103.

IL-12p40-dependent agonistic effects on the development of protective innate and adaptive immunity against Salmonella enteritidis

To study a potential IL-12p40-dependent but IL-12p75-independent agonistic activity regulating the immune response against Salmonella Enteritidis, the course of infection in IL-12p35-deficient mice (IL-12p35(-/-), capable of producing IL-12p40) was compared with that of IL-12p40(-/-) mice. Mice lacking IL-12p40 revealed a higher mortality rate and higher bacterial organ burden than mice capable of producing IL-12p40. This phenotype was found in both genetically susceptible (BALB/c, Ity(s)) and resistant mice (129Sv/Ev, Ity(r)) indicating Ity-independent mechanisms. The more effective control of bacteria in the IL-12p35(-/-) mice was associated with elevated serum IFN-gamma and TNF-alpha levels. In contrast, IL-12p40(-/-) mice showed reduced IFN-gamma production, which was associated with significantly elevated serum IgE levels. Early during infection (days 3 and 4 postinfection), as well as late (day 20 postinfection), the number of infected phagocytes was strongly increased in the absence of IL-12p40 indicating impaired bactericidal activity when IL-12p40 was missing. Liver histopathology revealed a decreased number of mononuclear granulomas in IL-12p40(-/-) mice. Depletion of CD4(+) or CD8(+) T lymphocytes in vivo suggested that both T cell subpopulations contribute to the IL-12p40-dependent protective functions. Analysis of IL-12p40 vs IL-23p19 mRNA expression revealed an up-regulation of only IL-12p40 mRNA during Salmonella infection. Together these data indicate that IL-12p40 can induce protective mechanisms during both the innate and the adaptive type 1 immune response in Salmonella infection. This novel activity of IL-12p40 complements the well described dominant and essential role of IL-12p75 in protective immunity to Salmonella infection.

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.

Molecular cloning and functional characterization of guinea pig IL-12

IL-12 is a heterodimeric cytokine that plays a central role in cell-mediated immunity. We cloned complete cDNAs of guinea pig homologues of IL-12 p35 and p40 subunits, and compared their functional properties with human IL-12. Both p35 and p40 mRNA were constitutively expressed in the testis and peritoneal macrophages. On immunoblotting, anti-guinea pig p40 antibody detected the constitutive expression of p40 protein in the testis, while in macrophages it was induced in response to lipopolysaccharide. An unidentified 200-kDa macromolecule was also expressed in the testis. All recombinant hybrid heterodimer p70 (guinea pig p70, human p70 and two interspecies heterodimers) exerted proliferative activity toward concanavalin A-primed guinea pig and human lymphoblasts in a dose-dependent manner. A similar tendency was observed in IFN-gamma production in IL-2-treated human lymphocytes. All hybrid heterodimers also induced IFN-gamma mRNA from IL-2-treated guinea pig splenocytes. Thus, unlike the current concept that the p35 subunit determines the species incompatibility of IL-12 in humans and mice, p35 has marginal ability to define its species-specific functional expression between humans and guinea pigs. In addition, constitutive expression of IL-12 or related molecules in the testis indicated a potential role of this molecule in regulation of physiological or pathophysiological conditions in the reproductive system.

IL-1 beta induces dendritic cells to produce IL-12

The cytokine IL-12, a product of dendritic cells (DC), plays a major role in cellular immunity, notably by inducing lymphocytes to produce IFN-gamma. Microbial products, T cell signals and cytokines induce the production of IL-12. Here, IL-1 beta is identified as a new IL-12-inducing agent, acting conjointly with CD40 ligand (CD40L) on human monocyte-derived DC in vitro. The effects of IL-1 beta were dose dependent, specifically blocked by neutralizing antibodies, and were observed both in immature and mature DC. Immature DC secreted more IL-12 than mature DC, but the effects of IL-1 beta were not due to a block of DC maturation as determined by analysis of DC surface markers. The mechanisms of action of IL-1 beta could be contrasted to that of other inducers of IL-12 such as IFN-gamma and lipopolysaccharide (LPS). Either IL-1 beta or IFN-gamma co-induced IL-12 with CD40L but conjointly, IL-1 beta, CD40L and IFN-gamma synergized, inducing very high levels of IL-12. The effects of IL-1 beta differed from those of LPS in that IL-1 beta, unlike LPS, could not induce IL-12 solely after IFN-gamma priming; and when combined with CD40L, IL-1 beta, unlike LPS, induced little IL-10. The mechanism of action of IL-1 beta involves IL-12 alpha mRNA up-regulation, and we show that the combination of CD40L and IL-1 beta induces high levels of IL-12 alpha and IL-12 beta mRNA in DC. Altogether, these results delineate a new mechanism linking adaptive and innate immune responses for the regulation of IL-12 production in DC and for the role of IL-1 beta in the development of cellular immunity.

Suppression of Il-12 transcription in macrophages following Fc gamma receptor ligation

Ligating Fc gamma R on macrophages results in suppression of IL-12 production. We show that Fc gamma R ligation selectively down-regulates IL-12 p40 and p35 gene expression at the level of transcription. The region responsive to this inhibition maps to the Ets site of the p40 promoter. PU.1, IFN consensus sequence binding protein, and c-REL: form a complex on this element upon macrophage activation. Receptor ligation abolishes the binding of this PU.1-containing activation complex, and abrogates p40 transcription. A dominant-negative construct of PU.1 diminishes IL-12 p40 promoter activity and endogenous IL-12 p40 protein secretion. Thus, the specificity of IL-12 down-regulation following receptor ligation lies in the inhibition of binding of a PU.1-containing complex to the Ets site of the IL-12 promoter. These findings provide evidence demonstrating for the first time the importance of PU.1 in the transcriptional regulation of IL-12 gene expression.

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.