Differential expression of miRNAs in canine peripheral blood mononuclear cells (PBMC) exposed to Leishmania infantum in vitro

Visceral Leishmaniasis (VL) is a neglected tropical disease, caused by L. infantum in the New World, where dogs are the main reservoir. These parasites can regulate host immune response through miRNA differential expression in the early stages of infection; however such early response has not yet been investigated in the canine model. PBMC from healthy dogs were exposed to L. infantum in vitro and microarray analysis showed an upregulation of miR-206, miR-302d, miR-433, miR-214, miR-493, miR-514, miR-1835, miR-210, miR-539, miR-432, miR-188, miR-345 and downregulation of miR-489 and miR-503 in comparison to non-exposed control cells, at 24 h post-exposure. In silico target prediction showed that the upregulated miRNAs target 1541 genes, which can modulate important pathways involved in the early immune responses, like the "MAPK signaling pathway", one of the most relevant pathways to Leishmania survival inside host cells. These findings shed light on parasite modulation of host immunity following Leishmania infection, which in turn can be explored for drug development.

Interleukin-10 but not transforming growth factor-β1 gene expression is up-regulated by vitamin D treatment in multiple sclerosis patients

Multiple sclerosis (MS) is an inflammatory and autoimmune disease. Variety of different genetics and environmental factors are involved in MS pathology. The epidemiological studies demonstrated that vitamin D has immune and immunomodulating effects on MS disease. Therefore, this study aims to evaluate the effect of vitamin D treatment on the expression of interleukin-10 (IL-10) and transforming growth factor-β1 (TGF-β1) genes in MS patients. We found that, the expression level of IL-10 gene in treated patients was up-regulated 3.84 times more than before treatment, but the expression level of TGF-β1 was not affected by vitamin D treatment. Also, a significant relationship was observed between vitamin D level and EDSS in MS patients. Our results indicated that the increased level of serum vitamin D and IL-10 gene expression may be associated with the reduction of EDSS scores in MS patients.

Enhanced IL-12p40 production in LPS-stimulated macrophages by inhibiting JNK activation by artemisinin

Artemisinin can be isolated from Artemisia annua L. In addition to its well-known anti-malarial activity, artemisinin has antitumor and anti-microbial effects. In this study, we investigated the effect of artemisinin on the production of IL-12p40, which is important in the generation of T helper 1 responses. Artemisinin significantly induced IL-12p40 production in LPS-stimulated RAW264.7 macrophage cells. To elucidate the signaling molecules regulated by artemisinin in induced IL-12p40 production, the DNA-binding activity of several transcription factors and activation of mitogen-activated protein kinase (MAPK)s were investigated. The band intensities of NF-κB, AP-1, and SP1, and the activation of p38 MAPK and ERK were not changed by artemisinin. However, the induced phosphorylation of JNK was significantly decreased by artemisinin, and inhibition of the JNK signaling pathway further increased IL-12p40 production in LPS-stimulated RAW264.7 macrophage cells. Taken together, these data suggest that artemisinin induces the production of IL-12p40 in LPS-stimulated macrophage cells by inhibiting JNK activity.

Glycoinositolphospholipids from Leishmania braziliensis and L. infantum: modulation of innate immune system and variations in carbohydrate structure

The essential role of the lipophosphoglycan (LPG) of Leishmania in innate immune response has been extensively reported. However, information about the role of the LPG-related glycoinositolphospholipids (GIPLs) is limited, especially with respect to the New World species of Leishmania. GIPLs are low molecular weight molecules covering the parasite surface and are similar to LPG in sharing a common lipid backbone and a glycan motif containing up to 7 sugars. Critical aspects of their structure and functions are still obscure in the interaction with the vertebrate host. In this study, we evaluated the role of those molecules in two medically important South American species Leishmania infantum and L. braziliensis, causative agents of visceral (VL) and cutaneous Leishmaniasis (CL), respectively. GIPLs derived from both species did not induce NO or TNF-α production by non-primed murine macrophages. Additionally, primed macrophages from mice (BALB/c, C57BL/6, TLR2-/- and TLR4-/-) exposed to GIPLs from both species, with exception to TNF-α, did not produce any of the cytokines analyzed (IL1-β, IL-2, IL-4, IL-5, IL-10, IL-12p40, IFN-γ) or p38 activation. GIPLs induced the production of TNF-α and NO by C57BL/6 mice, primarily via TLR4. Pre incubation of macrophages with GIPLs reduced significantly the amount of NO and IL-12 in the presence of IFN-γ or lipopolysaccharide (LPS), which was more pronounced with L. braziliensis GIPLs. This inhibition was reversed after PI-specific phospholipase C treatment. A structural analysis of the GIPLs showed that L. infantum has manose rich GIPLs, suggestive of type I and Hybrid GIPLs while L. braziliensis has galactose rich GIPLs, suggestive of Type II GIPLs. In conclusion, there are major differences in the structure and composition of GIPLs from L. braziliensis and L. infantum. Also, GIPLs are important inhibitory molecules during the interaction with macrophages.

The macrophage response towards LPS and its control through the p38(MAPK)-STAT3 axis

In macrophages detection of gram-negative bacteria particularly involves binding of the outer-wall component lipopolysaccharide (LPS) to its cognate receptor complex, comprising Toll like receptor 4 (TLR4), CD14 and MD2. LPS-induced formation of the LPS receptor complex elicits a signaling network, including intra-cellular signal-transduction directly activated by the TLR4 receptor complex as well as successional induction of indirect autocrine and paracrine signaling events. All these different pathways are integrated into the macrophage response towards an inflammatory stimulus by a highly complex cross-talk of the pathways engaged. This also includes a tight control by several intra- and inter-cellular feedback loops warranting an inflammatory response sufficient to battle invading pathogens and to avoid non-essential tissue damage caused by an overwhelming inflammatory response. Several evidences indicate that the reciprocal cross-talk between the p38(MAPK)-pathway and signal transducer and activator of transcription (STAT)3-mediated signal-transduction forms a critical axis successively activated by LPS. The balanced activation of this axis is essential for both induction and propagation of the inflammatory macrophage response as well as for the control of the resolution phase, which is largely driven by IL-10 and sustained STAT3 activation. In this context regulation of suppressor of cytokine signaling (SOCS)3 expression and the recently described divergent regulatory roles of the two p38(MAPK)-activated protein kinases MK2 and MK3 for the regulation of LPS-induced NF-κB- and IRF3-mediated signal-transduction and gene expression, which includes the regulation of IFNβ, IL-10 and DUSP1, appears to play an important role.

Tumor growth and metastasis suppression by Glipr1 gene-modified macrophages in a metastatic prostate cancer model

We previously identified the mouse and human Glipr1 and GLIPR1/RTVP-1 (respectively) genes as direct p53 targets with proapoptotic activities in various cancer cell lines, including prostate cancer. Intratumoral injection of an adenoviral vector capable of efficient transduction and expression of Glipr1 (AdGlipr1) yielded promising therapeutic results in an orthotopic, metastatic mouse model of prostate cancer. AdGlipr1-transduced macrophages (Mϕ/Glipr1) generated greater surface expression of CD40, CD80, and MHC class II molecules and greater production of interleukin (IL)-12 and IL-6 in vitro than control macrophages did. Mechanistic analysis indicated that increased production of IL-12 in Mϕ/Glipr1 depends on activation of the p38 signaling cascade. Mϕ/Glipr1 injected into orthotopic 178-2BMA tumors in vivo resulted in significantly suppressed prostate tumor growth and spontaneous lung metastases and longer survival relative to those observed in control-treated mice. Furthermore, these preclinical data indicate the generation of systemic natural killer-cell activity and tumor-specific cytotoxic T-lymphocyte responses. Trafficking studies confirmed that intratumorally injected Mϕ/Glipr1 could migrate to draining lymph nodes. Overall, our data suggest that this novel gene-modified cell approach is an effective treatment avenue that induces antitumor immune responses in preclinical studies.

Transcriptional suppression of IL-27 production by Mycobacterium tuberculosis-activated p38 MAPK via inhibition of AP-1 binding

Mycobacterium tuberculosis remains a major global challenge to human health care, and the mechanisms of how M. tuberculosis evades host immune surveillance to favor its survival are still largely unknown. In this study, we found that bacillus Calmette-Guérin (BCG) and viable M. tuberculosis as well as M. tuberculosis lysates could activate IL-27 expression in human and mouse macrophages by induction of p28 subunit transcription. However, in parallel with these effects, BCG and M. tuberculosis lysate stimulation of macrophages induced activation of p38 MAPK signaling molecules MLK3/MKK3/MK2 to prevent maximal IL-27 production. M. tuberculosis lysate-induced p28 transcription was dependent on MyD88 signaling pathway. AP-1/c-Fos was shown to bind directly to the p28 promoter and induce p28 expression after M. tuberculosis lysate stimulation. Overexpression of p38α inhibited the binding of c-Fos to the p28 promoter but had no effect on c-Fos protein expression or phosphorylation in response to M. tuberculosis lysate stimulation. Furthermore, blockade of p38 by SB203580 enhanced M. tuberculosis-induced AP-1 binding to the p28 promoter. Importantly, we show that adding exogenous IL-27 to increase the levels produced by PBMCs stimulated with live mycobacteria enhanced the ability of BCG-expanded T cells to inhibit intracellular mycobacterial growth in human macrophages. Taken together, our data demonstrate that mycobacterial stimulation induces both IL-27 production and p38 MAPK activation. Strategies designed to tip the balance toward positive regulation of p28 induction by mycobacteria could lead to enhanced protective tuberculosis immunity.

Secretory mediators regulate Nod2-induced tolerance in human macrophages

BACKGROUND & AIMS

Nucleotide oligomerization domain 2 (Nod2) polymorphisms increase the risk of developing Crohn's disease, which is characterized by chronic intestinal inflammation. Bacterial peptidoglycan products chronically stimulate Nod2 in the intestine. Recent studies found that chronic Nod2 stimulation in human macrophages down-regulates proinflammatory cytokines on Nod2 or Toll-like receptor (TLR) restimulation. Therefore, an emerging hypothesis is that Nod2-mediated cytokine down-regulation is required for intestinal homeostasis, but the mechanisms mediating this down-regulation are incompletely understood.

METHODS

Utilizing primary human macrophages, we examined secretory mediators as a mechanism of Nod2-mediated tolerance by inhibiting their function and assessing tolerance reversal through cytokine secretion. Signaling pathways contributing to secretory mediator induction and Nod2-mediated tolerance were identified through pathway inhibition.

RESULTS

We found that chronic Nod2 stimulation cross-tolerizes not only to TLRs but also to the interleukin (IL)-1 receptor. Moreover, chronic IL-1β stimulation down-regulates Nod2 responses. Accordingly, IL-1β blockade partially reverses Nod2-mediated tolerance. We found that an additional essential mechanism for Nod2-mediated tolerance is the early secretion of the anti-inflammatory mediators IL-10, transforming growth factor β, and IL-1Ra. Importantly, the mammalian target of rapamycin (mTOR) pathway, involved in cell growth, differentiation, and activation, significantly contributes to Nod2-induced anti-inflammatory as opposed to proinflammatory cytokines and to Nod2-mediated tolerance.

CONCLUSIONS

Inflammatory responses through the IL-1R are down-regulated upon chronic Nod2 stimulation, secretory mediators are a critical mechanism for Nod2-mediated cytokine down-regulation, and the mTOR pathway is crucial for Nod2-mediated tolerance. These results further contribute to our understanding of the mechanisms through which Nod2, a protein critical to intestinal homeostasis, down-regulates cytokine responses.

The regulation of Th1 responses by the p38 MAPK

IL-12 is a dimeric cytokine that is produced primarily by APCs. In this study we examined the role that the p38 MAPKs (MAPK/p38) play in regulating IL-12 production. We show that inhibition of p38 dramatically increased IL-12 production upon stimulation, while decreasing TNF-α. This reciprocal effect on these two cytokines following MAPK/p38 inhibition occurred in many different APCs, following a variety of different stimuli. IL-12 production was also increased in macrophages treated with small interfering RNA to limit p38α expression, and in macrophages deficient in MKK3, a kinase upstream of p38. The increase in IL-12 production following MAPK/p38 inhibition appears to be due to enhanced IL-12 (p40) mRNA stability. We show that MAPK/p38 inhibition can promote Th1 immune responses and thereby enhance vaccine efficacy against leishmaniasis. In a mouse model of Leishmania major infection, vaccination with heat-killed L. major plus CpG and SB203580 elicited complete protection against infection compared with heat-killed L. major plus CpG without SB203580. Thus, this work suggests that MAPK/p38 inhibitors may be applied as adjuvants to bias immune responses and improve vaccinations against intracellular pathogens.

Leishmania interferes with host cell signaling to devise a survival strategy

The protozoan parasite Leishmania spp. exists as extracellular promastigotes in its vector whereas it resides and replicates as amastigotes within the macrophages of its mammalian host. As a survival strategy, Leishmania modulates macrophage functions directly or indirectly. The direct interference includes prevention of oxidative burst and the effector functions that lead to its elimination. The indirect effects include the antigen presentation and modulation of T cell functions in such a way that the effector T cells help the parasite survive by macrophage deactivation. Most of these direct and indirect effects are regulated by host cell receptor signaling that occurs through cycles of phosphorylation and dephosphorylation in cascades of kinases and phosphatases. This review highlights how Leishmania selectively manipulates the different signaling pathways to ensure its survival.

Selective activation of the p38 MAPK pathway by synthetic monophosphoryl lipid A

TLR4 stimulation by lipopolysaccharide can cause both MAL/MyD88- and TRAM/TRIF (Toll IL-1 receptor domain-containing adaptor-inducing IFNbeta)-dependent signaling events. Monophosphoryl lipid A (MPLA), a low toxicity derivative of endotoxic lipopolysaccharide, enhances antibody responses, T cell expansion, and recall responses against antigens without causing excessive inflammatory side effects. Previously, we proposed that TRIF-biased activation of TLR4 by MPLA is responsible for its reduced toxicity while retaining potent adjuvant effects. However, some TRIF-associated genes, such as MCP-1, are only weakly expressed, and some MyD88-associated inflammatory and anti-inflammatory cytokines, such as tumor necrosis factor alpha and interleukin-10, are strongly activated after MPLA stimulation despite weak NF-kappaB but strong IRF3 activation. We now report that synthetic derivatives of MPLA retained TRIF bias as compared with synthetic diphosphoryl lipid A, indicating a change in a single phosphoryl group is sufficient for TRIF-biased TLR4 stimulation. We extend our previous observations by showing that sMLA induces strong p38 MAPK but weak JNK activation, resulting in high IP-10 (interferon-inducible protein 10), tumor necrosis factor alpha, and interleukin-10 but low MCP-1 transcript levels. Results of this study identify a novel biochemical mechanism for regulation of sMLA-induced gene expression.

Vav proteins control MyD88-dependent oxidative burst

The importance of reactive oxygen intermediate (ROI) production in antimicrobial responses is demonstrated in human patients who suffer from chronic granulomatous disease (CGD) due to defective NADPH oxidase function. Exactly how bacterial products activating Toll-like receptors (TLRs) induce oxidative burst is unknown. Here, we identify the Vav family of Rho guanine nucleotide exchange factors (GEFs) as critical mediators of LPS-induced MyD88-dependent activation of Rac2, NADPH oxidase, and ROI production using mice deficient in Vav1, Vav2, and Vav3. Vav proteins are also required for p38 MAPK activation and for normal regulation of proinflammatory cytokine production, but not for other MyD88-controlled effector pathways such as those involving JNK, COX2, or iNOS and the production of reactive nitrogen intermediates (RNIs). Thus, our data indicate that Vav specifically transduces a subset of signals emanating from MyD88.

Nitric oxide inhibits interleukin-12 p40 through p38 MAPK-mediated regulation of calmodulin and c-rel

In activated macrophages, the rel/NF-kappaB transcription factors are known to play important roles in interleukin-12 (IL-12) p40 regulation by nitric oxide (NO). However, the relative contributions of these factors are not well understood. Here, we describe a dominant role for c-rel involving p38 mitogen-activated protein kinase (p38 MAPK) and calmodulin (CaM) protein in NO-mediated IL-12 p40 inhibition in activated macrophages. Inhibition of NO production by aminoguanidine increased, whereas sodium nitroprusside (SNP; an exogenous NO generator) reduced, nuclear c-rel levels in LPS + IFN-gamma-activated RAW 264.7 macrophages. Overexpression of c-rel but not p65 NF-kappaB increased IL-12 p40 during NO treatment. The p38 MAPK phosphorylation is increased by NO, and inhibition of p38 MAPK in SNP-treated macrophages by SB203580 or transient expression of a dominant-negative mutant of p38 MAPK upregulated both nuclear c-rel and IL-12 p40 levels, indicating that NO targeted the p38 MAPK pathway to inhibit c-rel and IL-12 p40. Cytoplasmic CaM level was increased by NO, and SB203580 decreased the CaM level in NO-exposed macrophages. Inhibition of CaM activity by trifluoperazine rescued the inhibitory effect of NO on c-rel and IL-12 p40. Our findings indicate that c-rel plays an important role in NO-mediated inhibition of IL-12 p40 and is regulated by p38 MAPK through CaM protein.

Role of mitogen-activated protein kinases and NF-kappaB in the regulation of proinflammatory and anti-inflammatory cytokines by Porphyromonas gingivalis hemagglutinin B

Hemagglutinin B (HagB) is a nonfimbrial adhesin expressed on the surface of Porphyromonas gingivalis and has been implicated as a potential virulence factor involved in mediating the attachment of the bacteria to host cells. However, the molecular mechanisms underlying host responses to HagB and their roles in pathogenesis have yet to be elucidated. Mitogen-activated protein kinases (MAPKs) are activated following engagement of a variety of cell surface receptors via dual tyrosine and threonine phosphorylation and are thought to be involved in various cellular responses. The purpose of this study was to determine the role of intracellular signaling pathways including the MAPKs and NF-kappaB in regulating the production of proinflammatory and anti-inflammatory cytokines following stimulation of murine macrophages with recombinant HagB (rHagB). Stimulation of peritoneal macrophages with rHagB resulted in the production of the proinflammatory cytokines interleukin-12p40 (IL-12p40), gamma interferon (IFN-gamma), and tumor necrosis factor alpha, as well as the anti-inflammatory cytokine IL-10. We also demonstrated the activation of extracellular signal-related kinase (ERK), c-Jun NH2-terminal protein kinase (JNK), and p38 MAPKs by rHagB-stimulated macrophages. Furthermore, blocking of the ERK and p38 signaling pathways by using specific inhibitors revealed differential regulatory roles in the rHagB-mediated production of proinflammatory and anti-inflammatory cytokines. ERK and p38 were important in down-regulation of IL-12p40 and IFN-gamma production and up-regulation of IL-10 production. The enhanced levels of IL-12p40 in rHagB-stimulated macrophages by inhibition of ERK or p38 activity were partially attributable to the inhibition of IL-10 production. Moreover, NF-kappaB was found to be critical for up-regulation of IL-12p40 and down-regulation of IL-10 production in rHagB-stimulated macrophages. Taken together, our results demonstrate a role for the p38 and ERK pathways and the transcription factor NF-kappaB in modulating key immunoregulatory cytokines involved in the development of immune responses to P. gingivalis HagB.

Disparate expression of IL-12 by SJL/J and B10.S macrophages during Theiler's virus infection is associated with activity of TLR7 and mitogen-activated protein kinases

Differences in components of innate anti-viral immune responses may account for the contrast in susceptibility to Theiler's murine encephalomyelitis virus (TMEV) between SJL/J and B10.S mice. Herein, the expression of IL-12, interferon (IFN)-beta, Toll-like receptors 3 (TLR3), TLR7, and mitogen-activated protein (MAP)-kinases was evaluated in SJL/J and B10.S macrophages infected with TMEV. Twenty-four hours after infection, SJL/J macrophages exhibited higher levels of TMEV RNA, IL-12 p40, and TLR3 but lower levels of IL-12 p70 and the IL-12 p35 subunit compared with B10.S macrophages. Addition of exogenous IL-12 p70 or IFN-beta increased the resistance of SJL/J macrophages to TMEV infection. To assess MAP-kinases, macrophages were pretreated with the p38 MAP-kinase inhibitor SB203580 or extracellular signal-regulated kinases (ERK) MAP-kinase inhibitor U0126 before TMEV infection. U0126 reduced SJL/J but increased B10.S macrophage expression of IL-12 p40 and p70 in response to TMEV. U0126 decreased the IL-12 p35 response of SJL/J macrophages. To assess TLR7, SJL/J and B10.S macrophages were stimulated with loxoribine, a TLR7 ligand. Loxoribine induced more IL-12 p70 production and p35 expression in B10.S than SJL/J macrophages. U0126 increased loxoribine-induced expression of IL-12 p40 and IL-12 p70 in B10.S but not SJL/J macrophages. Thus, differences in production of IL-12 p70 due to expression of the p35 subunit and in activity of TLR7, as well as activation of factors downstream of ERK MAP-kinases likely underlie the disparity in innate immunity between SJL/J and B10.S macrophages to TMEV.

ERK-MAP-kinases differentially regulate expression of IL-23 p19 compared with p40 and IFN-beta in Theiler's virus-infected RAW264.7 cells

Theiler's murine encephalomyelitis virus (TMEV) infection of macrophages induces a demyelinating disease (DD) in certain strains of mice that is similar to human multiple sclerosis. In contrast to IFN-beta, expression of IL-23 p19 and p40 subunits by macrophages in response to TMEV may contribute to DD. TMEV infection of macrophages likely induces IL-23 and IFN-beta by activating p38 or ERK MAP-kinases (MAPK) and the p38 substrate ATF-2 within 30 min. To determine the role of MAPKs in TMEV-induced IL-23 and IFN-beta expression, RAW264.7 cells were pretreated with SB203580 or U0126, inhibitors of p38 and ERK MAPKs, respectively. SB203580 significantly increased TMEV-induced p19 but decreased p40 expression. In contrast, U0126 decreased p19 and increased TMEV-induced p40 and IFN-beta expression. Interestingly, U0126 prolonged TMEV-induced ATF-2 activation to at least 3h. Thus ERK MAPKs regulate expression of TMEV-induced p19 differently than p40 and IFN-beta suggesting the benefits of U0126 in treatment of DD.

Regulation and Phenotype of an Innate Th1 Cell: Role of Cytokines and the p38 Kinase Pathway

We have explored the phenotype and regulation of Th1 cell activation by the cytokines IL-12 and IL-18. We demonstrate that these two cytokines selectively induce IFN-gamma in a differentiated Th1 cell population through the previously described p38 mitogen-activated protein (MAP) kinase pathway. Using a highly selective p38 MAP kinase inhibitor, we demonstrate that it is possible to block IFN-gamma induction from activated, differentiated Th1 cells via p38 MAP kinase without disrupting the activation and differentiation of naive T cells or the proliferation of naive or differentiated T cells. In addition, IL-12 and IL-18 provide an Ag and IL-2-independent survival signal to this uniquely differentiated Th1 cell population. We hypothesize that this Ag-independent survival of Th1 cells may participate in an innate inflammatory loop with monocytes at the sites of chronic inflammation. In addition, p38 MAP kinase inhibition of this cytokine-regulated pathway may be a unique mechanism to inhibit chronic inflammation without disruption of Ag-driven activation and function of naive T cells.

Increased brain injury and vascular leakage after pretreatment with p38-inhibitor SB203580 in transient ischemia

OBJECTIVES

Focal cerebral ischemia activates intracellular signaling pathways including the mitogen-activated protein kinase p38, which may be involved in the process of ischemic brain injury. In this study, the effect of pretreatment with the p38-inhibitor SB203580 on infarct size and blood-brain barrier (BBB) breakdown was investigated with magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Rats were given SB203580 (n = 6) or vehicle (n = 6) in the right lateral ventricle prior to transient (90 min) middle cerebral artery occlusion (MCAO) on the left side. The rats were examined with serial MRI during MCAO, at reperfusion and after 1 and 4 days.

RESULTS

The mean infarct size on T2-weighted images after 1 day was significantly higher in the SB203580-treated group than in controls (300 +/- 95 mm3 vs 126 +/- 75 mm3; P < 0.01). Vascular gadolinium leakage, indicating BBB breakdown, was significantly larger in the SB203580-treated group than in controls after 1 day (median leakage score 18.5; range 15-21 vs 6.5; 4-17; P < 0.05) and 4 days (11; 6-15 vs 3.5; 1-9; P < 0.05), although no significant difference was seen initially.

CONCLUSION

Pretreatment with SB203580 may aggravate ischemic brain injury and cerebral vascular leakage in the present model of transient ischemia.

Mechanisms of immune resolution

Initially after injury, the innate/proinflammatory and some aspects of the acquired immune response are up-regulated to maintain a defense against foreign pathogens, clear tissue debris present at the wound site, and orchestrate aspects of tissue remodeling, cell proliferation and angiogenic process, associated with the wound response. However, for proper wound healing to progress, this initial inflammatory response has to be regulated or shut down so as to allow for the reestablishment of matrix, recellularization, and tissue remodeling. Inability to properly resolve the extent of innate/acquired response at a site of injury can lead to poor wound healing, immune suppression, and recurrent infectious episodes. This review attempts to summarize information on regulatory mechanisms that are thought to be involved in controlling/resolving innate or acquired immune responses so as to provide a framework for use in thinking about the impact these processes and their manipulation may have on wound healing and its potential management.

Role of the phosphatidylinositol 3 kinase-Akt pathway in the regulation of IL-10 and IL-12 by Porphyromonas gingivalis lipopolysaccharide

Stimulation of the APC by Porphyromonas gingivalis LPS has been shown to result in the production of certain pro- and anti-inflammatory cytokines. However, the signaling pathways that regulate these processes are currently unknown. In the present study, the role of the phosphatidylinositol 3 kinase (PI3K)-Akt pathway in regulating P. gingivalis LPS-induced production of IL-10, IL-12 p40, and IL-12 p70 by human monocytes was investigated. P. gingivalis LPS selectively activates the PI3K-Akt pathway via Toll-like receptor 2, and inhibition of this pathway results in an abrogation of extracellular signal-regulated kinase 1/2 phosphorylation, whereas the activation of p38 and c-Jun N-terminal kinase 1/2 kinases were unaffected. Analysis of cytokine production following stimulation of monocytes with P. gingivalis LPS revealed that inhibition of the PI3K pathway differentially regulated IL-10 and IL-12 synthesis. IL-10 production was suppressed, whereas IL-12 levels were enhanced. Inhibition of P. gingivalis LPS-mediated activation of the PI3K-Akt pathway resulted in a pronounced augmentation of NF-kappaB p65 that was independent of IkappaB-alpha degradation. Furthermore, the ability of the PI3K-Akt pathway to modulate IL-10 and IL-12 production appears to be mediated by the selective suppression of extracellular signal-regulated kinase 1/2 activity, as the MEK1 inhibitor PD98059 closely mimicked the effects of wortmannin and LY294002 to differentially regulate IL-10 and IL-12 production by P. gingivalis LPS-stimulated monocytes. These studies provide new insight into how engagement of the PI3K-Akt pathway by P. gingivalis LPS affects the induction of key immunoregulatory cytokines that control both qualitative and quantitative aspects of innate and adaptive immunity.

Defining the involvement of p38alpha MAPK in the production of anti- and proinflammatory cytokines using an SB 203580-resistant form of the kinase

Despite its lack of specificity, the inhibitor SB 203580 has been widely used to implicate p38 mitogen-activated protein kinase (MAPK) in the synthesis of many cytokines. Here we show unequivocally that the production of interleukin (IL)-1beta, IL-6, IL-10, and tumor necrosis factor alpha (TNFalpha) requires p38 MAPK activity by demonstrating that the inhibitory effects of SB 203580 were reversed by expression of an SB 203580-resistant form of p38alpha (SBR-p38alpha) that fails to bind to SB 203580. This strategy established the requirement for p38 activity for the lipopolysaccharide-stimulated production of IL-10, IL-1beta, and IL-6 by the monocytic cell WEHI 274 and the production of IL-6 and TNFalpha stimulated by ligation of the Fc-gamma receptor of the mast cell MC/9. Expression of SBR-p38alpha in primary macrophages abrogated the ability of SB 203580 to inhibit the lipopolysaccharide-stimulated production of TNFalpha but not of IL-10. Expression of SBR-p38alpha in primary T lymphocytes abrogated the ability of SB 203580 to inhibit the production of interferon-gamma induced by co-ligation of CD3 and CD28 but not the production of interferon-gamma or IL-10 induced by IL-12. These results suggest that the levels of p38 MAPK activity required for maximal cytokine production vary with different cytokines and stimuli.

Role of innate immune factors in the adjuvant activity of monophosphoryl lipid A

Monophosphoryl lipid A (MPL) is a nontoxic derivative of lipopolysaccharide (LPS) that exhibits adjuvant properties similar to those of the parent LPS molecule. However, the mechanism by which MPL initiates its immunostimulatory properties remains unclear. Due to the involvement of Toll-like receptors in recognizing and transducing intracellular signals in response to LPS, the aim of the present study was to determine the ability of MPL to utilize the Toll-like receptor 2 (TLR2) and TLR4. We provide evidence that MPL differentially utilizes TLR2 and TLR4 for the induction of tumor necrosis factor alpha, interleukin 10 (IL-10), and IL-12 by purified human monocytes as well as by human peripheral blood mononuclear cells. Assessment of NF-kappa B activity demonstrated that MPL utilized TLR2 and especially TLR4 for the activation of NF-kappa B p65 by human monocytes. In addition, stimulation of human monocytes by MPL led to an up-regulation of the costimulatory molecules CD80 and CD86, an effect that could be reduced by pretreatment of cells with a monoclonal antibody to TLR2 or TLR4. Analysis of MPL-induced activation of the extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein (MAP) kinases revealed that MPL utilized both TLR2 and TLR4 for the phosphorylation of ERK1/2, while TLR4 was the predominant receptor involved in the ability of MPL to phosphorylate p38. Moreover, using selective inhibitors for MAP kinase kinase (PD98059) and p38 (SB203580), we show that ERK1/2 exhibited differential effects on production of TNF-alpha and IL-12 p40 by human monocytes, whereas MPL-induced activation of p38 appeared to be predominantly involved in production of IL-10 and IL-12 p40 by MPL-stimulated monocytes. Taken together, these findings aid in understanding the cellular mechanisms by which MPL induces host cell activation and subsequent adjuvant properties.