Dynamic Structural Differences between Human and Mouse STING Lead to Differing Sensitivity to DMXAA

The stimulator-of-interferon-genes (STING) protein is involved in innate immunity. It has recently been shown that modulation of STING can lead to an aggressive antitumor response. DMXAA is an antitumor agent that had shown great promise in murine models but failed in human clinical trials. The molecular target of DMXAA was subsequently shown to be murine STING (mSTING); however, human STING (hSTING) is insensitive to DMXAA. Molecular dynamics simulations were employed to investigate the differences between hSTING and mSTING that could influence DMXAA binding. An initial set of simulations was performed to investigate a single lid region mutation G230I in hSTING (corresponding residue in mSTING is an Ile), which rendered the protein sensitive to DMXAA. The simulations found that an Ile side chain was enough to form a steric barrier that prevents exit of DMXAA, whereas in WT hSTING, the Gly residue that lacks a side chain formed a porous lid region that allowed DMXAA to exit. A second set of molecular dynamics simulations compared the tendency of STING to be in an open-inactive conformation or a closed-active conformation. The results show that hSTING prefers to be in an open-inactive conformation even with cGAMP, the native ligand, bound. On the other hand, mSTING prefers a closed-active conformation even without a ligand bound. These results highlight the challenges in translating a mouse active STING compound into a human active compound, while also providing avenues to pursue for designing a small-molecule drug targeting human STING.     

The Chemotherapeutic Agent DMXAA as a Unique IRF3-Dependent Type-2 Vaccine Adjuvant

5,6-Dimethylxanthenone-4-acetic acid (DMXAA), a potent type I interferon (IFN) inducer, was evaluated as a chemotherapeutic agent in mouse cancer models and proved to be well tolerated in human cancer clinical trials. Despite its multiple biological functions, DMXAA has not been fully characterized for the potential application as a vaccine adjuvant. In this report, we show that DMXAA does act as an adjuvant due to its unique property as a soluble innate immune activator. Using OVA as a model antigen, DMXAA was demonstrated to improve on the antigen specific immune responses and induce a preferential Th2 (Type-2) response. The adjuvant effect was directly dependent on the IRF3-mediated production of type-I-interferon, but not IL-33. DMXAA could also enhance the immunogenicity of influenza split vaccine which led to significant increase in protective responses against live influenza virus challenge in mice compared to split vaccine alone. We propose that DMXAA can be used as an adjuvant that targets a specific innate immune signaling pathway via IRF3 for potential applications including vaccines against influenza which requires a high safety profile.     

The in vitro bactericidal activity of peritoneal and spleen cells from Listeria-resistant and -susceptible mouse strains

Two days after Listeria-resistant (LrR) C57BL/10 mice were infected intraperitoneally with Listeria, their peritoneal macrophages demonstrated enhanced bactericidal activity beyond that seen in susceptible (LrS) BALB/c or CBA mice. Intravenous infection had no effect on peritoneal cell activity. The induction, but not expression, of the enhanced activity was radiosensitive. There was no significant difference between the strains with respect to the number of cells or cellular composition of the exudates. No difference in the in vitro chemotactic response of cells from the two strains could be demonstrated. Therefore there seems to be recruitment to the infected peritoneal cavity of C57BL/10 mice of young, efficiently bactericidal monocytes/macrophages. On the other hand, spleen cell bactericidal activity was intrinsically superior in C57BL/10 mice compared with BALB/c mice, possibly because, as a haemopoietic organ, the C57BL/10 spleen already contains high numbers of these efficient monocytes.     

Effects of human alveolar macrophages on the induction of lymphokine (IL 2)-activated killer cells

Normal human alveolar macrophages (AM) significantly and reproducibly suppress induction of IL 2-activated killer (LAK) cell activity against allogeneic Burkitt's lymphoma (Daudi) cells. Incubation of purified peripheral blood lymphocytes for 4 days with autologous AM and 1 U/ml of IL 2 resulted in AM-mediated suppression of LAK activity, whereas peripheral blood monocytes isolated freshly by centrifugal elutriation from the same donor potentiated induction of LAK activity by IL 2. The suppression of LAK cell induction by human AM was dependent on the density of AM added to the lymphocyte cultures. Recombinant IFN-gamma did not affect AM-mediated suppression of LAK cell induction by IL 2. Both AM and monocytes stimulated with lipopolysaccharide markedly suppressed LAK cell induction by IL 2. AM-mediated down-regulation was seen only when AM were added immediately after the start of incubation of lymphocytes with IL 2; AM potentiated LAK activity when added 1 day later. Similar AM-mediated suppression of LAK cell induction was observed with four lines of allogeneic lung cancer cells as targets for LAK activity. These results indicate that AM may be important in regulation of in situ induction of LAK activity in the lung.     

Regulation of aminopeptidase-N (CD13) and Fc epsilon RIIb (CD23) expression by IL-4 depends on the stage of maturation of monocytes/macrophages.

IL-4 has multiple biologic activities and it has been shown to have effects on B and T lymphocytes, mast cells, NK cells, and monocytes. We studied the influence of IL-4 on the expression of cell membrane determinants, in particular aminopeptidase-N (CD13) and Fc epsilon RIIb (CD23), on human peripheral blood monocytes. We compared the response of monocytes with the response of human alveolar macrophages and monocytic cell lines (U937 and THP1), as mature and more immature representatives of the mononuclear phagocyte system, respectively. A dose-dependent increase of the expression of CD13 Ag was observed when monocytes were cultured with IL-4. Kinetic analyses revealed that this induction was maximal after 2 to 3 days of culture and resembled the kinetics of IL-4-induced expression of Fc epsilon RIIb on monocytes. This IL-4-induced increase was absent when monocytes were cultured with IL-4 and an anti-IL-4 antiserum. Concomitantly, an IL-4-induced increase in leucine-aminopeptidase activity could be observed. Northern blot analysis showed that incubation of monocytes with IL-4 induced a marked increase in CD13 mRNA. Alveolar macrophages also exhibited an increase in CD13 Ag expression when exposed to IL-4. Surprisingly, IL-4 was unable to induce expression of Fc epsilon RIIb on alveolar macrophages. U937 and THP1 cells did not show an induction of CD13 Ag when cultured in the presence of IL-4. However, IL-4 did induce the expression of Fc epsilon RIIb on both cell lines, suggesting the presence of functional IL-4R. Our data demonstrate that IL-4 increases the expression of CD13 Ag on monocytes. This IL-4-induced increase can also be observed in more mature monocytic cells such as alveolar macrophages, but is absent in immature cells such as U937 or THP1 cells. This is functionally accompanied by an increase in leucine-aminopeptidase activity and may be part of the general activation of monocytes/macrophages by IL-4. In conclusion, the data suggest that IL-4 responsiveness, in particular the induction of CD13 Ag and Fc epsilon RIIb expression, may be dependent on the stage of maturation of monocytes/macrophages.     

Production of a 26,000-dalton interleukin 1 inhibitor by human monocytes is regulated by granulocyte-macrophage colony-stimulating factor

An interleukin 1 (IL 1) inhibitor is secreted into culture medium by a human promyelocytic cell line, H-161, upon stimulation with (PMA) and recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF). Since the morphological characteristics of this cell line were macrophage-like, human monocytes were tested for their ability to produce similar activity using the same induction conditions. Upon induction of adherent peripheral blood monocytes with rhGM-CSF and/or PMA, an IL 1 antagonistic activity was found in the cell supernatants, as determined by IL 1 receptor binding assay, using the murine EL-4.6.1C10 cell line as the cell target. Most of the inhibition of IL 1 binding induced by PMA or by PMA/rhGM-CSF was shown to be caused by IL 1, since it was neutralized by a mixture of anti-IL 1 alpha/beta antibodies and was active in the murine thymocyte proliferation assay (LAF). The activity induced by GM-CSF alone was not neutralized by anti-IL 1 alpha/beta antibodies and showed no LAF activity. The IL 1 inhibitor activity was induced by rhGM-CSF with a D50 around 40 pg/ml. The activity was produced for more than 3 wk in the presence of GM-CSF; removal of GM-CSF was followed by a rapid decrease of IL 1 antagonistic activity. The specific binding of biosynthetically labeled IL 1 inhibitor to target cells (EL-4.6.1C10) showed a protein of 26 kDa as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). This molecule shares biological and physical characteristics with the urinary IL 1 inhibitor and the promyelocytic H-161-derived IL 1 inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)     

5,6-Dimethylxanthenone-4-acetic Acid (DMXAA) Activates Stimulator of Interferon Gene (STING)-dependent Innate Immune Pathways and Is Regulated by Mitochondrial Membrane Potential

The chemotherapeutic agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) is a potent inducer of type I IFNs and other cytokines. This ability is essential for its chemotherapeutic benefit in a mouse cancer model and suggests that it might also be useful as an antiviral agent. However, the mechanism underlying DMXAA-induced type I IFNs, including the host proteins involved, remains unclear. Recently, it was reported that the antioxidant N-acetylcysteine (NAC) decreased DMXAA-induced TNF-α and IL-6, suggesting that oxidative stress may play a role. The goal of this study was to identify host proteins involved in DMXAA-dependent signaling and determine how antioxidants modulate this response. We found that expression of IFN-β in response to DMXAA in mouse macrophages requires the mitochondrial and endoplasmic reticulum resident protein STING. Addition of the antioxidant diphenylene iodonium (DPI) diminished DMXAA-induced IFN-β, but this decrease was independent of both the NADPH oxidase, Nox2, and de novo generation of reactive oxygen species. Additionally, IFN-β up-regulation by DMXAA was inhibited by agents that target the mitochondrial electron transport chain and, conversely, loss of mitochondrial membrane potential correlated with diminished innate immune signaling in response to DMXAA. Up-regulation of Ifnb1 gene expression mediated by cyclic dinucleotides was also impaired by DPI, whereas up-regulation of Ifnb1 mRNA due to cytosolic double-stranded DNA was not. Although both stimuli signal through STING, cyclic dinucleotides interact directly with STING, suggesting that recognition of DMXAA by STING may also be mediated by direct interaction.     

Cooperation between an anti-T cell (anti-CD28) monoclonal antibody and monocyte-produced IL-6 in the induction of T cell responsiveness to IL-2

CD28 is an Ag of 44-kDa Mr that is expressed on the membrane of the majority of human T cells and that is recognized by mAb 9.3. The functional effects of mAb 9.3 on peripheral blood T cells were studied. mAb 9.3 was not mitogenic, unless it was combined with PMA. When CD28 was cross-linked after binding of mAb 9.3 to the T cell by immobilized or soluble anti-mouse IgG, T cells proliferated in response to rIL-2, provided that monocytes were also present. The additional signal required for IL-2 responsiveness after cross-linking of CD28 could also be delivered in cultures of purified T cells by a cellfree monocyte culture supernatant. Expression of IL-2R on about 10% of the T cells was demonstrated by staining with an anti-IL-2R mAb, and was found to be largely restricted to CD4+ cells. The active compound responsible for the helper signal in the monocyte culture supernatant was identified as IL-6 because purified IL-6 (but not IL-1 beta) had similar activity and because an antiserum to IL-6 (but not an antiserum to IL-1 beta) neutralized the activity of the monocyte supernatant and blocked T cell proliferation. An anti-IL-2R antibody also completely inhibited T cell proliferation induced by the combination of mAb 9.3, IL-2, and IL-6. Our results provide evidence that cross-linking of CD28 induces functional IL-2R and that this activity is dependent on a helper signal provided by monocytes, more specifically IL-6. Moreover, our results indicate that IL-6 (previously called B cell stimulatory factor-2) is active on T cells. If a natural ligand for CD28 can be identified, the mechanism of induction of IL-2 responsiveness described here might explain how T cells become nonspecifically involved in an ongoing cellular immune reaction.     

The davDT operon of Pseudomonas putida, involved in lysine catabolism, is induced in response to the pathway intermediate delta-aminovaleric acid

Pseudomonas putida KT2440 is a soil microorganism that attaches to seeds and efficiently colonizes the plant's rhizosphere. Lysine is one of the major compounds in root exudates, and P. putida KT2440 uses this amino acid as a source of carbon, nitrogen, and energy. Lysine is channeled to delta-aminovaleric acid and then further degraded to glutaric acid via the action of the davDT gene products. We show that the davDT genes form an operon transcribed from a single sigma70-dependent promoter. The relatively high level of basal expression from the davD promoter increased about fourfold in response to the addition of exogenous lysine to the culture medium. However, the true inducer of this operon seems to be delta-aminovaleric acid because in a mutant unable to metabolize lysine to delta-aminovaleric acid, this compound, but not lysine, acted as an effector. Effective induction of the P. putida P(davD) promoter by exogenously added lysine requires efficient uptake of this amino acid, which seems to proceed by at least two uptake systems for basic amino acids that belong to the superfamily of ABC transporters. Mutants in these ABC uptake systems retained basal expression from the davD promoter but exhibited lower induction levels in response to exogenous lysine than the wild-type strain.     

Vascular disrupting agent drug classes differ in effects on the cytoskeleton

Vascular disrupting agents (VDAs), anti-cancer drugs that target established tumor blood vessels, fall into two main classes: microtubule targeting drugs, exemplified by combretastatin A4 (CA4), and flavonoids, exemplified by 5,6-dimethylxanthenone-4-acetic acid (DMXAA). Both classes increase permeability of tumor vasculature in mouse models, and DMXAA in particular can cause massive tumor necrosis. The molecular target of CA4 is clearly microtubules. The molecular target(s) of DMXAA remains unclear. It is thought to promote inflammatory signaling in leukocytes, and has been assumed to not target microtubules, though it is not clear from the literature how carefully this assumption has been tested. An earlier flavone analog, flavone acetic acid, was reported to promote mitotic arrest suggesting flavones might possess anti-microtubule activity, and endothelial cells are sensitive to even mild disruption of microtubules. We carefully investigated whether DMXAA directly affects the microtubule or actin cytoskeletons of endothelial cells by comparing effects of CA4 and DMXAA on human umbilical vein endothelial cells (HUVEC) using time-lapse imaging and assays for cytoskeleton integrity. CA4 caused retraction of the cell margin, mitotic arrest and microtubule depolymerization, while DMXAA, up to 500 μM, showed none of these effects. DMXAA also had no effect on pure tubulin nucleation and polymerization, unlike CA4. We conclude that DMXAA exhibits no direct anti-microtubule action and thus cleanly differs from CA4 in its mechanism of action at the molecular level.     

The role of protein tyrosine phosphorylation in integrin-mediated gene induction in monocytes

Integrin-mediated cell adhesion, or cross-linking of integrins using antibodies, often results in the enhanced tyrosine phosphorylation of certain intracellular proteins, suggesting that integrins may play a role in signal transduction processes. In fibroblasts, platelets, and carcinoma cells, a novel tyrosine kinase termed pp125FAK has been implicated in integrin-mediated tyrosine phosphorylation. In some cell types, integrin ligation or cell adhesion has also been shown to result in the increased expression of certain genes. Although it seems reasonable to hypothesize that integrin-mediated tyrosine phosphorylation and integrin-mediated gene induction are related, until now, there has been no direct evidence supporting this hypothesis. In the current report, we explore the relationship between integrin- mediated tyrosine phosphorylation and gene induction in human monocytes. We demonstrate that monocyte adherence to tissue culture dishes or to extracellular matrix proteins is followed by a rapid and profound increase in tyrosine phosphorylation, with the predominant phosphorylated component being a protein of 76 kD (pp76). Tyrosine phosphorylation of pp76 and other monocyte proteins can also be triggered by incubation of monocytes with antibodies to the integrin beta 1 subunit, or by F(ab')2 fragments of such antibodies, but not by F(ab) fragments. The ligation of beta 1 integrins with antibodies or F(ab')2 fragments also induces the expression of immediate-early (IE) genes such as IL-1 beta. When adhering monocytes are treated with the tyrosine kinase inhibitors genistein or herbimycin, both phosphorylation of pp76 and induction of IL-1 beta message are blocked in a dose-dependent fashion. Similarly, treatment with genistein or herbimycin can block tyrosine phosphorylation of pp76 and IL-1 beta message induction mediated by ligation of beta 1 integrin with antibodies. These observations suggest that protein tyrosine phosphorylation is an important aspect of integrin-mediated IE gene induction in monocytes. The cytoplasmic tyrosine kinase pp125FAK, although important in integrin signaling in other cell types, seems not to play a role in monocytes because this protein could not be detected in these cells.     

Subcellular localization of human monocyte interleukin 1: evidence for an inactive precursor molecule and a possible mechanism for IL 1 release

IL 1 activity, as assayed by the proliferation of responsive mouse thymocytes and a human astrocytoma cell line, was detected on the membrane of 1% paraformaldehyde-fixed activated human monocytes. Resting, unactivated monocytes did not display IL 1 activity. Maximum induction of membrane IL 1 was obtained from monocytes treated with polyclonal activators, such as LPS or Staphylococcus aureus, whereas adherence was a weak inducer of membrane IL 1. Isolated cell compartments as plasma membranes, crude lysosomes, and crude cytosol from activated human monocytes expressed significant IL 1 activity, whereas the endoplasmic reticulum showed no IL 1 activity. Exposure to trypsin of either fixed, activated human monocytes or cell compartments from unfixed monocytes, revealed biologically active IL 1 in the membrane, crude lysosome, and crude cytosol, but not in the endoplasmic reticulum. The IL 1 activity in the purified cytosol, prepared by extraction with digitonin, was considerably increased by the trypsin treatment, whereas the increase in IL 1 activity within crude lysosomes and plasma membranes was less. The cell compartments from nonactivated monocytes did not express active IL 1 and trypsin treatment revealed no active IL 1, suggesting the absence of a pool of the trypsin-sensitive form of IL 1. The data confirm the presence of membrane-bound IL 1 in activated human monocytes and indicate that an inactive precursor molecule can be found in the cytosol of such cells. Furthermore, the absence of IL 1 activity either in its active form or as the inactive precursor in the endoplasmic reticulum suggests that IL 1 is not a conventionally secreted protein. Because IL 1 was found in the cytosol as a precursor and in the lysosomal fractions in an active form, these data suggest that after the synthesis and processing of the cytosolic precursor, the 17-kda IL 1, is released via lysosomal vesicles.     

Acid phosphatase and non-specific alpha-naphthol acetate esterase activities of monocytes in patients with cancer of the digestive tract during surgical treatment

In 22 patients with cancer of the alimentary tract the activities of acid phosphatase and non-specific alpha-naphthol acetate esterase in monocytes were tested. The enzyme activity was tested in the peripheral blood before surgical intervention, in blood from vessels draining the tumour before its excision and in the peripheral blood before surgical intervention, in blood from vessels draining the tumour before its excision and in the peripheral blood 2--3 weeks after tumour excision. In parallel tests the enzyme activity was estimated in the peripheral blood of 22 healthy individuals. The study indicates that the non-specific alpha-naphthol acetate esterase activity of monocytes derived from patients with cancer and control group did not show a marked difference. The acid phosphatase activity in monocytes derived from a tumour efferent vessel was found to be higher in majority of the cases than the activity of this enzyme in monocytes derived from the peripheral blood. After removing the tumour the acid phosphatase activity of monocytes was elevated in half of the cases. It seems possible that the increase of acid phosphatase activity in monocytes derived from cancer patients may be due to the activation of monocytes in contact with cancer antigens or antigen-antibody complexes.     

Induction of IFN-alpha in peripheral blood mononuclear cells by HIV-infected monocytes. Restricted antiviral activity of the HIV-induced IFN.

PBMC cocultured with HIV-infected monocytes for 12 to 48 h released high levels of IFN activity. IFN titers were directly dependent upon time after virus infection and level of HIV replication in infected cells. IFN induction in PBMC was evident with HIV-infected monocytes and PBMC and with myeloid and lymphoblastoid cell lines with at least three different HIV strains. In HIV-infected cell line pairs in which virus infection occurs in both productive and restricted forms, IFN induction in PBMC occurred only with productive infection. IFN activity was acid stable and completely neutralized by antibodies against IFN-alpha. Induction of IFN required cell-cell contact between HIV-infected cells and PBMC, but was independent of MHC compatibility. With PBMC co-cultured with autologous HIV-infected monocytes, IFN induction was highly selective: IL-1 beta, IL-6, or TNF-alpha activity and mRNA were not detected. Cell surface determinants on HIV-infected monocytes that induced IFN in PBMC remained active after fixation in 4% paraformaldehyde. Both adherent and nonadherent PBMC produced IFN after coculture with HIV-infected monocytes. Ability to produce IFN by PBMC was not affected by depletion of T cell, NK cell, B cell, or monocyte subpopulations. The IFN activity produced by PBMC cocultured with HIV-infected cells was about 20-fold less active than equal quantities of rIFN-alpha 2b for inhibition of HIV replication in monocytes and at low concentrations enhanced virus growth. Clinical studies with HIV-infected patients and parallel findings in animal lentivirus disease suggest an adverse role for IFN in disease progression. Conditions for induction of IFN in the culture system described in this report may mimic those in the HIV-infected patient. Defining the molecular basis for IFN induction, the cells that produce IFN, and the altered biologic activity of this important cytokine may provide insight into the pathogenesis of HIV disease.     

Response of nitric oxide production to CpG oligodeoxynucleotides in turkey and chicken peripheral blood monocytes

We evaluated the innate immune response to various synthetic CpG-containing oligodeoxynucleotides (CpG ODNs) by measuring nitric oxide production in the peripheral blood monocytes from turkey poults. The results indicate that the presence of the CpG dinucleotide in ODNs was a prerequisite for activation of turkey monocytes and induction of nitric oxide (NO) synthesis. CpG motifs and sequence structure of the ODNs were also found to influence stimulatory activity greatly. The most potent CpG ODN to induce NO synthesis in turkey monocytes was human-specific CpG ODN M362, followed by CpG ODN 2006 (human), CpG ODN#17 (chicken) and CpG ODN 1826 (mouse). The optimal CpG motif for NO induction was GTCGTT. Phosphorothioate modification of CpG ODNs also significantly increased stimulatory activity. Compared with chicken monocytes, turkey monocytes appeared to be less sensitive to CpG motif variation, whereas chicken monocytes were found to respond more strictly to human-specific CpG ODNs or ODNs that contain GTCGTT motifs.     

Refractoriness of interferon-beta signaling through NOD1 pathway in mouse respiratory epithelial cells using the anticancer xanthone compound

AIM:To explore the possibility that nucleotide oligomerization domain 1(NOD1) pathway involved in refractoriness of interferon-β signaling in mouse respiratory epithelial cells induced by the anticancer xanthone compound,5,6-dimethylxanthenone-4-acetic acid(DMXAA).METHODS:C10 mouse bronchial epithelial cells were grown in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum,2 mmol/L glutamine,100 units/mL penicillin,100 g/mL streptomycin.Pathogen-free female BALB/c mice were used to explore the mechanisms of refractoriness of interferon-signaling.Mouse thioglycollate-elicited peritoneal macrophages,bone marrow derived macrophages and bone marrow derived dendritic cells were collected and cultured.The amount of interferon(IFN)-inducible protein-10(IP10/CXCL10),macrophage chemotactic protein(MCP1/CCL2) and interleukin(IL)-6 secreted by cells activated by DMXAA was quantified using enzyme-linked immunosorbent assay kits according to the instructions of the manufacturers.Total RNA was isolated from cells or nasal epithelium with RNeasy Plus Mini Kit,and cDNA was synthesized.Gene expression was checked using Applied Biosystems StepOne Real-Time Polymerase Chain Reaction System.Transfection of small interfering RNA(siRNA) control,NOD1 duplexed RNA oligonucleotides,and high-mobility group box 1/2/3(HMGB1/2/3) siRNA was performed using siRNA transfection reagent.RESULTS:DMXAA activates IFN-β pathway with high level of IFN-β dependent antiviral genes including 2',5'-oligoadenylate synthetase 1 and myxovirus resistance 1 in mouse thioglycollate-elicited peritoneal macrophages,bone marrow derived macrophages and bone marrow derived dendritic cells.Activation of IFN-β by DMXAA involved in NOD1,but not HMGB1/2/3 signal pathway demonstrated by siRNA.NOD1 pathway plays an important role in refractoriness of IFN-β signaling induced by DMXAA in mouse C10 respiratory epithelial cells and BALB/c mice nasal epithelia.These data indicate that DMXAA is not well adapted to the intrinsic properties of IFN-β signaling.Approaches to restore sensitivity of IFN-β signaling by find other xanthone compounds may function similarly,could enhance the efficacy of protection from influenza pneumonia and potentially in other respiratory viral infections.CONCLUSION:NOD1 pathway may play an important role in refractoriness of IFN-β signaling in mouse respiratory epithelial cells induced by DMXAA.     

Monocyte chemotaxis and activating factor production by keratinocytes in response to IFN-gamma

Monocytes accumulate in the epidermis and along the dermo-epidermal junction in several different inflammatory skin diseases. To determine whether human epidermal keratinocytes elaborate a specific chemotaxin responsible for the accumulation of monocytes at these anatomic sites, monocyte chemotactic activity in conditioned 16-h cultured keratinocyte supernatants were assayed using human peripheral blood monocytes as the target cell. Dilutional analysis revealed directed monocyte migration in IFN-gamma-treated (100 U/ml) keratinocyte supernatants (80% maximal FMLP response) which was 10-fold more than IFN-gamma itself or untreated keratinocyte activity alone. Gel filtration chromatography revealed that this activity eluted just ahead of a 12.5-kDa molecular mass marker. Blocking studies demonstrated that a rabbit polyclonal antibody to monocyte chemotaxis and activating factor (MCAF) inhibited all monocyte chemotaxis by greater than 80%. Keratinocytes were metabolically labeled with 35S-cysteine/methionine, and after 16 h incubation the supernatants immunoprecipitated with the same anti-MCAF antibody. MCAF was detected as a protein doublet of 12 and 9 kDa only in IFN-gamma-treated (100 U/ml) keratinocyte supernatants. Incubation with IFN-gamma and TNF-alpha (250 U/ml) in combination resulted in increased production of MCAF protein. By Northern blot analysis, MCAF mRNA was constitutively expressed in keratinocytes and upregulated only in the presence of IFN-gamma. TNF-alpha, IL-1 beta, transforming growth factor-beta and phorbol esters had no positive or negative influence on MCAF mRNA. These studies demonstrate that biologically active MCAF is elaborated by human epidermal keratinocytes upon activation by IFN-gamma, a cytokine also required for the induction of adherence between monocytes and keratinocytes. Keratinocyte-derived MCAF is likely to be important in the regulation of cutaneous monocyte trafficking and may also be responsible for the recruitment of Langerhans cells and dermal dendrocytes, which share many phenotypic features with monocytes/macrophages, to their anatomic locations in skin.     

Comparative analysis of CD137 and LPS effects on monocyte activation, survival, and proliferation

CD137 (ILA/4-1BB), a member of the TNF receptor family, regulates activation, survival and proliferation of primary human monocytes. Here we compare the activities of lipopolysaccharide (LPS), a classical and potent monocyte activator to that of CD137. LPS is a more potent activator of monocytes, as evidenced by a stronger induction of the proinflammatory cytokine IL-8. However, CD137 could further increase maximal cytokine induction by LPS, which points to separate signaling pathways for LPS and CD137. Also, expression of myc was only induced by the combination of CD137 and LPS. Expression of macrophage colony-stimulating factor is induced more potently by CD137, but an additive effect is obtained by the combination of CD137 and LPS. Monocyte/macrophage survival and proliferation is only induced by CD137. LPS counteracts both activities of CD137 via activation induced cell death. While LPS has a role in activation of monocytes in innate immunity, the CD137 receptor/ligand system seems to deliver an activating signal to monocyte in acquired immunity.