IL-18 Induces Monocyte Chemotactic Protein-1 Production in Macrophages through the Phosphatidylinositol 3-Kinase/Akt and MEK/ERK1/2 Pathways

Monocyte chemoattractant protein 1 regulates pulmonary host defense via neutrophil recruitment during Escherichia coli infection

Neutrophil accumulation is a critical event to clear bacteria. Since uncontrolled neutrophil recruitment can cause severe lung damage, understanding neutrophil trafficking mechanisms is important to attenuate neutrophil-mediated damage. While monocyte chemoattractant protein 1 (MCP-1) is known to be a monocyte chemoattractant, its role in pulmonary neutrophil-mediated host defense against Gram-negative bacterial infection is not understood. We hypothesized that MCP-1/chemokine (C-C motif) ligand 2 is important for neutrophil-mediated host defense. Reduced bacterial clearance in the lungs was observed in MCP-1(-/-) mice following Escherichia coli infection. Neutrophil influx, along with cytokines/chemokines, leukotriene B(4) (LTB(4)), and vascular cell adhesion molecule 1 levels in the lungs, was reduced in MCP-1(-/-) mice after infection. E. coli-induced activation of NF-κB and mitogen-activated protein kinases in the lung was also reduced in MCP-1(-/-) mice. Administration of intratracheal recombinant MCP-1 (rMCP-1) to MCP-1(-/-) mice induced pulmonary neutrophil influx and cytokine/chemokine responses in the presence or absence of E. coli infection. Our in vitro migration experiment demonstrates MCP-1-mediated neutrophil chemotaxis. Notably, chemokine receptor 2 is expressed on lung and blood neutrophils, which are increased upon E. coli infection. Furthermore, our findings show that neutrophil depletion impairs E. coli clearance and that exogenous rMCP-1 after infection improves bacterial clearance in the lungs. Overall, these new findings demonstrate that E. coli-induced MCP-1 causes neutrophil recruitment directly via chemotaxis as well as indirectly via modulation of keratinocyte cell-derived chemokine, macrophage inflammatory protein 2, and LTB(4).

MCP-1/CCL2 modifies axon properties in a PMP22-overexpressing mouse model for Charcot-Marie-tooth 1A neuropathy

Charcot-Marie-Tooth 1A (CMT1A) neuropathy, the most common inherited peripheral neuropathy, is primarily caused by a gene duplication for the peripheral myelin protein-22 (PMP22). In an accordant mouse model, we investigated the role of monocyte chemoattractant protein-1 (MCP-1/CCL2) as a regulator of nerve macrophages and neural damage including axonopathy and demyelination. By generating PMP22tg mice with reduced levels or lack of MCP-1/CCL2, we found that MCP-1/CCL2 is involved in the increase of macrophages in mutant nerves. PMP22tg mice with wild-type levels of MCP-1/CCL2 showed strong macrophage increase in the diseased nerves, whereas either 50% reduction or total absence of MCP-1/CCL2 led to a moderate or a strong reduction of nerve macrophages, respectively. Interestingly, MCP-1/CCL2 expression level and macrophage numbers were correlated with features indicative of axon damage, such as maldistribution of K+ channels, reduced compound muscle action potentials, and muscle weakness. Demyelinating features, however, were most highly reduced when MCP-1/CCL2 was diminished by 50%, whereas complete lack of MCP-1/CCL2 showed an intermediate demyelinating phenotype. We also identified the MEK1/2-ERK1/2-pathway as being involved in MCP-1/CCL2 expression in the Schwann cells of the CMT1A model. Our data show that, in a CMT1A model, MCP-1/CCL2 activates nerve macrophages, mediates both axon damage and demyelination, and may thus be a promising target for therapeutic approaches.

Interleukin-18 exacerbates pulmonary injury after hepatic ischemia/reperfusion in mice

BACKGROUND

Hepatic ischemia/reperfusion has been shown to cause both local hepatic and distant organ (such as lung) injury caused by accumulation of neutrophils in the local and distant organs, leading to neutrophil-dependent organ injury. Interleukin (IL) -18 is required for facilitating neutrophil-dependent local hepatic injury by suppressing anti-inflammatory cytokine expression, but less is known about the involvement of this cytokine in distant organ injury. The objective of this study was to determine whether IL-18 contributes to pulmonary injury induced by hepatic ischemia/reperfusion.

METHODS

C57BL/6 mice and IL-18 knockout mice (C57BL/6 background) were subjected to 90 min of partial hepatic ischemia and subsequent reperfusion. Neutrophil accumulation in the lung was assessed by pulmonary myeloperoxidase contents. Pulmonary expressions of keratinocyte derived chemokine (KC, CXCL1), macrophage chemoattractant protein-1 (MCP-1, CCL2), tumor necrosis factor-alpha, interferon-gamma, IL-4, and IL-10 were measured by tissue enzyme-linked immunosorbent assay (ELISA). Lung edema was quantified by the pulmonary wet to dry weight ratios.

RESULTS

Hepatic ischemia/reperfusion caused significant increases in pulmonary neutrophil recruitment and lung edema. Also, pulmonary expression of KC and MCP-1 were up-regulated. In the IL-18 knockout mice, hepatic ischemia/reperfusion-induced increases in pulmonary neutrophil recruitment, lung injury defined by lung edema, and pulmonary chemokine expression were attenuated. Furthermore, pulmonary expression of an anti-inflammatory cytokine IL-4 and systemic IL-10 expression were significantly up-regulated in the IL-18 knockout mice.

CONCLUSIONS

The data suggested that IL-18 plays an important role in the development of pulmonary injury after hepatic ischemia/reperfusion by up-regulating proinflammatory mediators and possibly suppressing anti-inflammatory cytokine expression.

The macrophage: the intersection between HIV infection and atherosclerosis

HIV-infected individuals are at increased risk of coronary artery disease (CAD) with underlying mechanisms including chronic immune activation and inflammation secondary to HIV-induced microbial translocation and low-grade endotoxemia; direct effects of HIV and viral proteins on macrophage cholesterol metabolism; and dyslipidemia related to HIV infection and specific antiretroviral therapies. Monocytes are the precursors of the lipid-laden foam cells within the atherosclerotic plaque and produce high levels of proinflammatory cytokines such as IL-6. The minor CD14+/CD16+ "proinflammatory" monocyte subpopulation is preferentially susceptible to HIV infection and may play a critical role in the pathogenesis of HIV-related CAD. In this review, the central role of monocytes/macrophages in HIV-related CAD and the importance of inflammation and cholesterol metabolism are discussed.

Etanercept reduces the serum levels of macrophage chemotactic protein-1 in patients with rheumatoid arthritis

This study was performed to analyze the effect of etanercept, the soluble tumor necrosis factor-alpha (TNF-alpha) receptor, on the serum levels of several chemokines including monocyte chemotactic protein-1 (MCP-1), regulated upon activation normal T expressed and presumably secreted (RANTES), and granzyme B in rheumatoid arthritis (RA) patients. Twenty-eight patients with RA were administered etanercept once or twice a week for more than 6 months. Clinical and laboratory parameters were measured and serum levels of MCP-1, RANTES, and granzyme B were determined using enzyme-linked immunosorbent assay (ELISA) kits at baseline and at 3 and 6 months after the initial treatment. In addition, the levels of MCP-1, RANTES, and granzyme B produced by cultured synovial cells stimulated with TNF-alpha were measured. A significant decrease in serum MCP-1 levels was observed at 3 and 6 months after initial treatment with etanercept. Serum RANTES and granzyme B levels did not show significant changes. TNF-alpha induced MCP-1, RANTES, and granzyme B production in cultured synovial cells from RA patients. Serum MCP-1 levels were significantly correlated with the disease activity scores of 28 joints combined with CRP (DAS28-CRP), indicating the role of MCP-1 in the pathogenesis of rheumatoid inflammation. This study demonstrated that a reduction of MCP-1 production in RA patients was a newly determined effect of etanercept. Another cascade not associated with TNF-alpha may induce granzyme B and RANTES production in RA patients.

A role for IL-18 in human neutrophil apoptosis

Decreased neutrophil apoptosis is associated with persistent inflammation, the severity of which correlates with serum IL-18 levels. IL-18 receptors as well as Toll-like receptors, including Toll-like receptor 4, a receptor for LPS, possess a highly conserved intracellular domain called "Toll-IL-1R domain" and activate overlapping signaling pathways. Here, we show that IL-18 modulates neutrophil apoptosis and compare its mechanism of action with LPS. We found that both IL-18 and LPS decreased neutrophil apoptosis in a similar dose- and time-dependent fashion. However, pretreatment with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 increased apoptosis more effectively in IL-18- than in LPS-stimulated cells, whereas the ERK inhibitor PD98059 had the same effect in both. In contrast, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 had no influence on apoptosis at all. Neutrophils constitutively expressed mRNA for IL-18 receptor beta, but little or no receptor alpha, both of which increased during coculture with either IL-18 or LPS in a time- and dose-dependent manner. Of the Bcl-2 family, antiapoptotic A1/Bfl-1 tended to increase on IL-18 and LPS stimulation, but was further increased despite increased apoptosis in the presence of MAPK inhibitors. Thus, human neutrophils can express mRNA for IL-18 receptors alpha and beta, and IL-18, like LPS, inhibits neutrophil apoptosis by activating PI3K and ERK pathways but not p38MAPK. However, PI3K may play more important role(s) in IL-18- than in LPS-induced inhibition of apoptosis. Mitogen-activated protein kinases seem to mediate antiapoptotic signals through factors other than Bcl-2 gene family expression.

Role of protein kinase C and phosphoinositide 3-kinase-Akt in substance P-induced proinflammatory pathways in mouse macrophages

Neuropeptide modulation of immune cell function is an important mechanism of neuro-immune intersystem crosstalk. Substance P (SP) is one such key neuropeptide involved. In this study, we investigated the yet unexplored cellular mechanisms of SP-mediated inflammatory responses in macrophages using a mouse macrophage-like cell line RAW 264.7 and isolated peritoneal macrophages. We found that the conventional PKCalpha and novel PKCdelta and epsilon were selectively activated by SP via its primary neurokinin-1 receptor (NK-1R) on the cells. Activation of these PKC isoforms mediated the activation of downstream extracellular signal-regulated kinase-1/2 (ERK1/2) and the transcription factor NF-kappaB, which drove the transcription of inducible chemokines in macrophages. Additionally, phosphoinositide 3-kinase (PI3K)-Akt was also activated by SP/NK-1R in macrophages. Inhibition of PI3K-Akt pathway attenuated ERK1/2 and NF-kappaB activation, suggesting it also played a part in SP-induced cellular inflammatory response. Kinetic analysis indicated that PKC isoforms induced early ERK1/2 activation, while PI3K-Akt contributed to the pathway at later time points. It was further demonstrated that PKC and PI3K-Akt were activated independent of each other. Collectively, our results suggest that SP/NK-1R activates two convergent proinflammatory signaling pathways, PKCs and PI3K-Akt, resulting in ERK1/2 and NF-kappaB activation and chemokine production in mouse macrophages.

Different inflammatory responses are associated with Ureaplasma parvum-induced UTI and urolith formation

Background

Epidemiologic studies show a strong association between Ureaplasmas and urogenital tract disease in humans. Since healthy humans can be colonized with Ureaplasmas, its role as a pathogen remains controversial. In order to begin to define the role of the host in disease, we developed a rodent model of urinary tract infection (UTI) using Fischer 344 (F344) rats. Animals were inoculated with sterile broth, 10¹, 10³, 10⁵, 10⁷, or 10⁹ log CFU of a rat-adapted strain of Ureaplasma parvum.

Results

Infected animals exhibited two distinct profiles, asymptomatic UTI and UTI complicated with struvite urolithiasis. Inoculum dose of U. parvum affected the incidence of UTI, and 50% to 57% of animals inoculated with ≥ 10⁷ CFU of U. parvum remained infected (p < 0.04). However, inoculum dose did not influence immune response to U. parvum. Asymptomatic UTI was characterized by a minimal immune response that was predominantly monocytic and lymphocytic, with limited lesions, and elevated urinary levels of IFN-γ, IL-18 and MCP-1 (P ≤ 0.02). UTI complicated with struvite formation was characterized by an exaggerated immune response that was mostly neutrophilic (P ≤ 0.0001), with lesions that showed extensive uroepithelial hyperplasia (P ≤ 0.0001), and a predominance of IL-1α, IL-1β, and GRO/KC in the urine (P ≤ 0.02). Animals with asymptomatic UTI also had a significantly high rate of kidney infection (P ≤ 0.0005).

Conclusion

Complications associated with U. parvum infection are primarily dependent upon host-specific factors rather than Ureaplasma microbial load. The immune response in F344 rats is similar to that which occurs in humans with ureaplasmal associated disease. Therefore, this model of infection is a useful tool for elucidating U. parvum-host interactions that confer UTI and disease.

Interleukin 18 in the heart

IL-18, originally termed as interferon gamma (IFN-gamma) inducing factor, is a proinflammatory cytokine that belongs to the IL-1 cytokine superfamily. IL-18 plays an important role in immune, infectious, and inflammatory diseases due to its induction of IFN-gamma. However, accumulated evidence has demonstrated that other effects of IL-18 are independent of IFN-gamma. Here, we reviewed the current literatures regarding the role of IL-18 in the heart and cardiovascular system. Infiltrated neutrophils, resident macrophages, endothelial cells, smooth muscle cells, and cardiomyocytes in the heart are able to produce IL-18 in response to injury. IL-18 is produced as a biologically inactive precursor (pro-IL-18) that is activated by caspase 1 (the IL-1beta converting enzyme). Elevated IL-18 levels have been observed in cardiac tissue and circulation after myocardial I/R and sepsis. The possible cellular and molecular mechanisms concerning IL-18-induced myocardial injury include induction of inflammation, increased apoptosis, a cardiac hypertrophy effect, modulation of mitogen activated protein kinase activation, and changes in intracellular calcium. Finally, we briefly reviewed the therapeutic strategies for inhibiting IL-18's biological activity to protect cardiac tissue from injury.

Interleukin-18 binding protein transgenic mice are protected against ischemic acute kidney injury

IL-18 function is neutralized in IL-18 binding protein transgenic (IL-18BP Tg) mice. First, we determined whether IL-18BP Tg mice are protected against ischemic acute kidney injury (AKI). Ischemic AKI was induced by bilateral renal pedicle clamping. IL-18BP Tg mice were functionally and histologically protected against ischemic AKI as determined by blood urea nitrogen, serum creatinine, and acute tubular necrosis score. We have demonstrated that the injurious effect of IL-18 in the kidney is independent of neutrophils and lymphocytes. Thus the effect of IL-18 inhibition on renal macrophage infiltration was determined. The number of macrophages was significantly reduced in IL-18BP Tg compared with wild-type kidneys. To determine the cytokines and chemokines that are dependent on IL-18, we performed flow cytometry based assays. Multiple chemokines/cytokines, IL-3, IL-6, IL-15, IL-18, leukemia inhibitory factor, macrophage colony-stimulating factor, macrophage inflammatory protein-2, granulocyte-macrophage colony-stimulating factor, and monocyte chemotactic protein-1 were significantly increased in AKI vs. sham kidneys. Only CXCL1 (also known as KC or IL-8) was significantly increased in AKI vs. sham kidneys and significantly reduced in IL-18BP Tg AKI vs. wild-type AKI kidneys. To determine whether macrophages are the source of CXCL1 in the kidney, we depleted macrophages with liposomal encapsulated clodronate. CXCL1 was significantly decreased in macrophage-depleted vs. control AKI mice. In summary, in ischemic AKI in mice, 1) IL-18BP Tg mice are functionally and histologically protected, 2) macrophage infiltration in the kidney and CXCL1 are significantly reduced in IL-18BP Tg mice, and 3) macrophage depletion significantly reduces CXCL1 in the kidney. In conclusion, protection against ischemic AKI in IL-18BP Tg mice is associated with less macrophage infiltration and less production of CXCL1 in the kidney.

FTY720 rescue therapy in the dark agouti rat model of experimental autoimmune encephalomyelitis: expression of central nervous system genes and reversal of blood-brain-barrier damage

FTY720 (fingolimod) is an oral sphingosine-1 phosphate (S1P) receptor modulator in phase III development for the treatment of multiple sclerosis. To further investigate its mode of action, we analyzed gene expression in the central nervous system (CNS) during experimental autoimmune encephalomyelitis (EAE). FTY720 downregulated inflammatory genes in addition to vascular adhesion molecules. It decreased the matrix metalloproteinase gene MMP-9 and increased its counterregulator--tissue inhibitor of metalloproteinase, TIMP-1--resulting in a proteolytic balance that favors preservation of blood-brain-barrier (BBB) integrity. Furthermore, FTY720 reduced S1P lyase that increases the S1P concentration in the brain, in line with a marked reversal of neurological deficits and raising the possibility for enhanced triggering of S1P receptors on resident brain cells. This is accompanied by an increase in S1P(1) and S1P(5) in contrast with the attenuation of S1P(3) and S1P(4). Late-stage rescue therapy with FTY720, even up to 1 month after EAE onset, reversed BBB leakiness and reduced demyelination, along with normalization of neurologic function. Our results indicate rapid blockade of ongoing disease processes by FTY720, and structural restoration of the CNS parenchyma, which is likely caused by the inhibition of autoimmune T cell infiltration and direct modulation of microvascular and/or glial cells.

Human cytomegalovirus latent infection of myeloid cells directs monocyte migration by up-regulating monocyte chemotactic protein-1

Following primary infection, human cytomegalovirus (HCMV) establishes a latent infection in hematopoietic cells from which it reactivates to cause serious disease in immunosuppressed patients such as allograft recipients. HCMV is a common cause of disease in newborns and transplant patients and has also been linked with vascular diseases such as primary and post-transplant arteriosclerosis. A major factor in the pathogenesis of vascular disease is the CC chemokine MCP-1. In this study, we demonstrate that granulocyte macrophage progenitors (GMPs) latently infected with HCMV significantly increased expression of MCP-1 and that this phenotype was dependent on infection with viable virus. Inhibitors of a subset of G(alpha) proteins and PI3K inhibited the up-regulation of MCP-1 in latently infected cultures, suggesting that the mechanism underlying this phenotype involves signaling through a G-protein coupled receptor. In GMPs infected with the low passage viral strain Toledo, up-regulated MCP-1 was restricted to a subset of myeloid progenitor cells expressing CD33, HLA-DR, and CD14 but not CD1a, CD15, or CD16, and the increase in MCP-1 was sufficient to enhance migration of CD14(+) monocytes to latently infected cells. Latent HCMV-mediated up-regulation of MCP-1 provides a mechanism by which HCMV may contribute to vascular disease during the latent phase of infection or facilitate dissemination of virus upon reactivation from latency.

Transcriptome analysis of NF-kappaB- and phosphatidylinositol 3-kinase-regulated genes in human cytomegalovirus-infected monocytes

Human cytomegalovirus induces a proinflammatory monocyte following infection, and we have evidence that NF-kappaB and phosphatidylinositol 3-kinase [PI(3)K] are key mediators in this early activation. To begin to address how these signaling pathways are responsible for the rapid activation of infected monocytes, we examined the role that these pathways played in the transcriptome of infected monocytes. Global transcriptional profiling using cDNA microarrays revealed that a significant number of genes, including inflammatory genes, were regulated in an NF-kappaB- and/or PI(3)K-dependent manner, identifying the NF-kappaB and PI(3)K pathways as key cellular control points in the conversion of monocytes to an activated proinflammatory state following HCMV infection.

Yaba monkey tumor virus encodes a functional inhibitor of interleukin-18

Interleukin-18 (IL-18) is a critical proinflammatory cytokine whose extracellular bioactivity is regulated by a cellular IL-18 binding protein (IL-18BP). Many poxviruses have acquired variants of this IL-18BP gene, some of which have been shown to act as viral virulence factors. Yaba monkey tumor virus (YMTV) encodes a related family member, 14L, which is similar to the orthopoxvirus IL-18BPs. YMTV 14L was expressed from a baculovirus system and tested for its ability to bind and inhibit IL-18. We found that YMTV 14L bound both human IL-18 (hIL-18) and murine IL-18 with high affinity, at 4.1 nM and 6.5 nM, respectively. YMTV 14L was able to fully sequester hIL-18 but could only partially inhibit the biological activity of hIL-18 as measured by gamma interferon secretion from KG-1 cells. Additionally, 17 hIL-18 point mutants were tested by surface plasmon resonance for their ability to bind to YMTV 14L. Two clusters of hIL-18 surface residues were found to be important for the hIL-18-YMTV 14L interaction, in contrast to results for the Variola virus IL-18BP, which has been shown to primarily interact with a single cluster of three amino acids. The altered binding specificity of YMTV 14L most likely represents an adaptation resulting in increased fitness of the virus and affirms the plasticity of poxviral inhibitor domains that target cytokines like IL-18.

Interleukin-18 induces angiogenic factors in rheumatoid arthritis synovial tissue fibroblasts via distinct signaling pathways

OBJECTIVE

Interleukin-18 (IL-18) is a proinflammatory cytokine implicated in the pathogenesis of rheumatoid arthritis (RA). This study was undertaken to examine the role of IL-18 in up-regulating secretion of the angiogenic factors stromal cell-derived factor 1alpha (SDF-1alpha)/CXCL12, monocyte chemoattractant protein 1 (MCP-1)/CCL2, and vascular endothelial growth factor (VEGF) in RA synovial tissue (ST) fibroblasts, and the underlying signaling mechanisms involved.

METHODS

We used enzyme-linked immunosorbent assays, Western blotting, and chemical inhibitors/antisense oligodeoxynucleotides to signaling intermediates to assess the role of IL-18.

RESULTS

IL-18 significantly enhanced the production of SDF-1alpha/CXCL12, MCP-1/CCL2, and VEGF in RA ST fibroblasts, in a time- and concentration-dependent manner. IL-18-induced SDF-1alpha/CXCL12 up-regulation was dependent on JNK, p38 MAPK, phosphatidylinositol 3-kinase (PI3K), and NFkappaB. While IL-18-induced production of SDF-1alpha/CXCL12 was also dependent on protein kinase Cdelta (PKCdelta), production of MCP-1/CCL2 was dependent on PKCalpha, not PKCdelta. Additionally, RA ST fibroblast IL-18-induced MCP-1/CCL2 production was mediated by JNK, PI3K, and NFkappaB. In contrast, IL-18 did not induce secretion of RA ST fibroblast MCP-1/CCL2 or VEGF via p38 MAPK. IL-18-induced RA ST fibroblast production of VEGF was mediated mainly by JNK-2, PKCalpha, and NFkappaB. IL-18 induced phosphorylation of JNK, PKCdelta, p38 MAPK, and activating transcription factor 2 (ATF-2) in RA ST fibroblasts in a time-dependent manner, with JNK-2 being upstream of PKCdelta, ATF-2, and NFkappaB.

CONCLUSION

These data support the notion that IL-18 has a unique role in inducing the secretion of angiogenic SDF-1alpha/CXCL12, MCP-1/CCL2, and VEGF in RA ST fibroblasts, via distinct signaling intermediates.

Macrophages and their products in rheumatoid arthritis

PURPOSE OF REVIEW

Macrophages differentiate from peripheral-blood monocytes. Both monocytes and synovial macrophages are key players in rheumatoid arthritis. These cells are involved in the initiation and perpetuation of inflammation, leukocyte adhesion and migration, matrix degradation and angiogenesis. Macrophages express adhesion molecules, chemokine receptors and other surface antigens. They also secrete a number of chemokines, cytokines, growth factors, proteases and other mediators.

RECENT FINDINGS

Macrophage migration-inhibitory factor has drawn significant attention recently. This cytokine is involved in macrophage activation and cytokine production. Migration-inhibitory factor also regulates glucocorticoid sensitivity and may be a pathogenic link between rheumatoid arthritis and atherosclerosis. Novel macrophage-derived chemokines and chemokine receptors have been identified. Interleukin-10 may have several proinflammatory effects that may influence its action in rheumatoid arthritis. Several proteinases including cathepsin G are produced by macrophages during rheumatoid arthritis-associated inflammatory and angiogenic events. Antirheumatic drugs, imatinib, chemokine receptor inhibitors and other specific strategies may become included in the therapy of rheumatoid arthritis.

SUMMARY

Macrophages and their products are key players in the pathogenesis of rheumatoid arthritis and may be good therapeutic targets.

Mechanism of adjuvant activity of cationic liposome: phosphorylation of a MAP kinase, ERK and induction of chemokines

Cationic liposome has been effectively used as a delivery system for DNA and protein vaccines. Recently, we discovered that strong anti-tumor immunity could be generated when a peptide antigen (E7) was incorporated into 1,2-dioleoyl-3-trimethylammonium-propane (chloride salt) (DOTAP) cationic liposome. Therefore, DOTAP liposome exhibits not only efficient delivery capacity, but also a potent adjuvant activity. In this report, the molecular mechanism of the adjuvanticity was studied both in vitro and in vivo. Microarray of mRNA analysis demonstrated that several chemokine genes are up-regulated by DOTAP liposome, including CCL2, CCL3 and CCL4, upon treatment of dendritic cells (DC) with DOTAP liposomes. CCL2 induction was mediated through extracellular-signal-regulated kinase (ERK) pathway, demonstrated by specific inhibitors of ERK pathway and siRNA approaches. Furthermore, DOTAP-induced CCL2 expression is negatively regulated by the p38 pathway. Consistently, ERK activation by DOTAP is also negatively regulated by p38. Moreover, PI-3 kinase was shown to be involved in both activation of ERK and induction of CCL2 by DOTAP. DOTAP- induced CCL2 release was also confirmed in the draining lymph nodes. More importantly, inhibition of ERK pathway completely abolishes the CCL2 accumulation in the draining lymph nodes and attenuates anti-tumor activity of DOTAP/E7. In conclusion, DOTAP is an active lipid stimulator for DC resulting in ERK activation and CC chemokine induction. Our data elucidated one important mechanism of adjuvant activity of cationic liposome and could facilitate rational design of synthetic lipid based adjuvants.

Cellular targets of interleukin-18 in rheumatoid arthritis

Recent data are presented which indicate a critical role for interleukin (IL)-18 in rheumatoid arthritis (RA). The T cells and macrophages invading the synovium or in the synovial fluid are the chief cellular targets of IL-18 in RA. Neutrophils, dendritic cells and endothelial cells may also be cellular mediators of IL-18. The direct effect of IL-18 on fibroblast-like synoviocytes or chondrocytes may not be essential or important. In RA, IL-18, which is mainly produced by macrophages, activates T cells and macrophages to produce proinflammatory cytokines, chemokines, adhesion molecules and RANKL which, in turn, perpetuate chronic inflammation and induce bone and cartilage destruction.