Mouse Neutrophils Require JNK2 MAPK for Toxoplasma gondii-Induced IL-12p40 and CCL2/MCP-1 Release

Human neutrophil-like cells demonstrate antimicrobial responses to the chronic cyst form of Toxoplasma gondii

The protozoan parasite Toxoplasma gondii infects approximately 2.5 billion people worldwide. Infection induces a rapid dissemination of parasites throughout the body followed by the formation of lifelong cysts within neurons of the host brain. Both stages require a dynamic immune response comprised of both innate and adaptive cells. Neutrophils are a primary responding cell to acute infection and have been observed in the brain during murine chronic infection. Previous studies investigating human neutrophils found that invasion by Toxoplasma tachyzoites inhibits apoptosis of neutrophils, prolonging their survival under inflammatory conditions. Here, we demonstrate the differentiation of two distinct subsets following exposure of human neutrophil-like-cells (HNLC) to Toxoplasma cysts. In vitro stimulation and imaging studies show cyst-specific induction of cytokines and cyst clearance by HNLCs. Further testing demonstrates that aged HNLCs perform less phagocytosis of cysts compared to non-aged HNLCs. In conclusion, this study identifies a novel response of HNLCs to Toxoplasma cysts and may indicate a role for neutrophils in the clearance of cysts during human infection with Toxoplasma.

A persistent neutrophil-associated immune signature characterizes post-COVID-19 pulmonary sequelae

Interstitial lung disease and associated fibrosis occur in a proportion of individuals who have recovered from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection through unknown mechanisms. We studied individuals with severe coronavirus disease 2019 (COVID-19) after recovery from acute illness. Individuals with evidence of interstitial lung changes at 3 to 6 months after recovery had an up-regulated neutrophil-associated immune signature including increased chemokines, proteases, and markers of neutrophil extracellular traps that were detectable in the blood. Similar pathways were enriched in the upper airway with a concomitant increase in antiviral type I interferon signaling. Interaction analysis of the peripheral phosphoproteome identified enriched kinases critical for neutrophil inflammatory pathways. Evaluation of these individuals at 12 months after recovery indicated that a subset of the individuals had not yet achieved full normalization of radiological and functional changes. These data provide insight into mechanisms driving development of pulmonary sequelae during and after COVID-19 and provide a rational basis for development of targeted approaches to prevent long-term complications.

Activation of Host Cellular Signaling and Mechanism of Enterovirus 71 Viral Proteins Associated with Hand, Foot and Mouth Disease

Enteroviruses are members of the Picornaviridae family consisting of human enterovirus groups A, B, C, and D as well as nonhuman enteroviruses. Human enterovirus type 71 (EV71) has emerged as a major cause of viral encephalitis, known as hand, foot, and mouth disease (HFMD), in children worldwide, especially in the Asia-Pacific region. EV71 and coxsackievirus A16 are the two viruses responsible for HFMD which are members of group A enteroviruses. The identified EV71 receptors provide useful information for understanding viral replication and tissue tropism. Host factors interact with the internal ribosome entry site (IRES) of EV71 to regulate viral translation. However, the specific molecular features of the respective viral genome that determine virulence remain unclear. Although a vaccine is currently approved, there is no effective therapy for treating EV71-infected patients. Therefore, understanding the host-pathogen interaction could provide knowledge in viral pathogenesis and further benefits to anti-viral therapy development. The aim of this study was to investigate the latest findings about the interaction of viral ligands with the host receptors as well as the activation of immunerelated signaling pathways for innate immunity and the involvement of different cytokines and chemokines during host-pathogen interaction. The study also examined the roles of viral proteins, mainly 2A and 3C protease, interferons production and their inhibitory effects.

Adjunctive Immunotherapeutic Efficacy of N-Formylated Internal Peptide of Mycobacterial Glutamine Synthetase in Mouse Model of Tuberculosis

BACKGROUND

Host-directed therapies are a comparatively new and promising method for the treatment of tuberculosis. A variety of host pathways, vaccines and drugs have the potential to provide novel adjunctive therapies for the treatment of tuberculosis. In this connection, we have earlier reported the immunotherapeutic potential of N-formylated N-terminal peptide of glutamine synthetase of Mycobacterim tuberculosis H37Rv (Mir SA and Sharma S, 2014). Now in the present study, we investigated the immunotherapeutic effect of N-terminally formylated internal-peptide 'f- MLLLPD' of mycobacterial glutamine synthetase (Rv2220) in mouse model of tuberculosis.

METHODS

The N-terminally formylated peptide, f-MLLLPD was tested for its potential to generate Reactive Oxygen Species (ROS) in murine neutrophils. Further, its therapeutic effect alone or in combination with anti-tubercular drugs was evaluated in mouse model of tuberculosis.

RESULTS

The f-MLLLPD peptide treatment alone and in combination with ATDs reduced the bacterial load (indicated as colony forming units) in lungs of infected mice by 0.58 (p<0.01) and 2.92 (p<0.001) log10 units respectively and in their spleens by 0.46 (p<0.05) and 2.46 (p<0.001) log10 units respectively. In addition, the observed histopathological results correlated well with the CFU data.

CONCLUSION

The results of the current study show that f-MLLLPD peptide confers an additional therapeutic efficacy to the anti-tuberculosis drugs.

Immunotherapeutic potential of an N-formylated peptide of Listeria monocytogenes in experimental tuberculosis

Objective: The current therapeutic regimens for tuberculosis (TB) are complex and involve the prolonged use of multiple antibiotics with diverse side effects that lead to therapeutic failure and bacterial resistance. The standard appliance of immunotherapy may aid as a powerful tool to combat the ensuing threat of TB. We have earlier reported the immunotherapeutic potential of N-formylated peptides of two secretory proteins of Mycobacterium tuberculosis H₃₇Rv. Here, we investigated the immunotherapeutic effect of an N-formylated peptide from Listeria monocytogenes in experimental TB. Methods: The N-terminally formylated listerial peptide with amino acid sequence 'f-MIGWII' was tested for its adjunctive therapeutic efficacy in combination with anti-tuberculosis drugs (ATDs) in the mouse model of TB. In addition, its potential to generate reactive oxygen species (ROS) in murine neutrophils was also evaluated. Results: The LemA peptide (f-MIGWII) induced a significant increase in the intracellular ROS levels of mouse neutrophils (p ≤ .05). The ATD treatment reduced the colony forming units (CFU) in lungs and spleen of infected mice by 2.39 and 1.67 log₁₀ units, respectively (p < .001). Treatment of the infected mice with combination of ATDs and LemA peptide elicited higher therapeutic efficacy over ATDs alone. The histopathological changes in the lungs of infected mice also correlated well with the CFU data. Conclusions: Our results clearly indicate that LemA peptide conferred an additional therapeutic effect when given in combination with the ATDss (p < .01) and hence can be used as adjunct to the conventional chemotherapy against TB.

JNK2 modulates the CD1d-dependent and -independent activation of iNKT cells

Invariant natural killer T (iNKT) cells play critical roles in autoimmune, anti-tumor, and anti-microbial immune responses, and are activated by glycolipids presented by the MHC class I-like molecule, CD1d. How the activation of signaling pathways impacts antigen (Ag)-dependent iNKT cell activation is not well-known. In the current study, we found that the MAPK JNK2 not only negatively regulates CD1d-mediated Ag presentation in APCs, but also contributes to CD1d-independent iNKT cell activation. A deficiency in the JNK2 (but not JNK1) isoform enhanced Ag presentation by CD1d. Using a vaccinia virus (VV) infection model known to cause a loss in iNKT cells in a CD1d-independent, but IL-12-dependent manner, we found the virus-induced loss of iNKT cells in JNK2 KO mice was substantially lower than that observed in JNK1 KO or wild-type (WT) mice. Importantly, compared to WT mice, JNK2 KO mouse iNKT cells were found to express less surface IL-12 receptors. As with a VV infection, an IL-12 injection also resulted in a smaller decrease in JNK2 KO iNKT cells as compared to WT mice. Overall, our work strongly suggests JNK2 is a negative regulator of CD1d-mediated Ag presentation and contributes to IL-12-induced iNKT cell activation and loss during viral infections.

Role of moesin in HMGB1-stimulated severe inflammatory responses

Sepsis is a life-threatening condition that arises when the body’s response to infection causes systemic inflammation. High-mobility group box 1 (HMGB1), as a late mediator of sepsis, enhances hyper-permeability, and it is therefore a therapeutic target. Despite extensive research into the underlying mechanisms of sepsis, the target molecules controlling vascular leakage remain largely unknown. Moesin is a cytoskeletal protein involved in cytoskeletal changes and para-cellular gap formation. The objectives of this study were to determine the roles of moesin in HMGB1-mediated vascular hyperpermeability and inflammatory responses and to investigate the mechanisms of action underlying these responses. Using siRNA knockdown of moesin expression in primary human umbilical vein endothelial cells (HUVECs), moesin was found to be required in HMGB1-induced F-actin rearrangement, hyperpermeability, and inflammatory responses. The mechanisms involved in moesin phosphorylation were analysed by blocking the binding of the HMGB1 receptor (RAGE) and inhibiting the Rho and MAPK pathways. HMGB1-treated HUVECs exhibited an increase in Thr558 phosphorylation of moesin. Circulating levels of moesin were measured in patients admitted to the intensive care unit with sepsis, severe sepsis, and septic shock; these patients showed significantly higher levels of moesin than healthy controls, which was strongly correlated with disease severity. High blood moesin levels were also observed in cecal ligation and puncture (CLP)-induced sepsis in mice. Administration of blocking moesin antibodies attenuated CLP-induced septic death. Collectively, our findings demonstrate that the HMGB1-RAGE-moesin axis can elicit severe inflammatory responses, suggesting it to be a potential target for the development of diagnostics and therapeutics for sepsis.

Hsa-let-7c-5p augments enterovirus 71 replication through viral subversion of cell signaling in rhabdomyosarcoma cells

Background

Human enterovirus 71 (EV71) causes severe hand, foot and mouse disease, accompanied by neurological complications. During the interaction between EV71 and the host, the virus subverts host cell machinery for its own replication. However, the roles of microRNAs (miRNAs) in this process remain obscure.

Results

In this study, we found that the miRNA hsa-let-7c-5p was significantly upregulated in EV71-infected rhabdomyosarcoma cells. The overexpression of hsa-let-7c-5p promoted replication of the virus, and the hsa-let-7c-5p inhibitor suppressed viral replication. Furthermore, hsa-let-7c-5p targeted mitogen-activated protein kinase kinase kinase kinase 4 (MAP4K4) and inhibited its expression. Interestingly, downregulation of MAP4K4 expression led to an increase in EV71 replication. In addition, MAP4K4 knockdown or transfection with the hsa-let-7c-5p mimic led to activation of the c-Jun NH2-terminal kinase (JNK) signaling pathway, whereas the hsa-let-7c-5p inhibitor inhibited activation of this pathway. Moreover, EV71 infection promoted JNK pathway activation to facilitate viral replication.

Conclusions

Our data suggested that hsa-let-7c-5p facilitated EV71 replication by inhibiting MAP4K4 expression, which might be related to subversion of the JNK pathway by the virus. These results may shed light on a novel mechanism underlying the defense of EV71 against cellular responses. In addition, these findings may facilitate the development of new antiviral strategies for use in future therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13578-017-0135-9) contains supplementary material, which is available to authorized users.

In silico identification of an aryl hydrocarbon receptor antagonist with biological activity in vitro and in vivo

The aryl hydrocarbon receptor (AHR) is critically involved in several physiologic processes, including cancer progression and multiple immune system activities. We, and others, have hypothesized that AHR modulators represent an important new class of targeted therapeutics. Here, ligand shape-based virtual modeling techniques were used to identify novel AHR ligands on the basis of previously identified chemotypes. Four structurally unique compounds were identified. One lead compound, 2-((2-(5-bromofuran-2-yl)-4-oxo-4H-chromen-3-yl)oxy)acetamide (CB7993113), was further tested for its ability to block three AHR-dependent biologic activities: triple-negative breast cancer cell invasion or migration in vitro and AHR ligand-induced bone marrow toxicity in vivo. CB7993113 directly bound both murine and human AHR and inhibited polycyclic aromatic hydrocarbon (PAH)- and TCDD-induced reporter activity by 75% and 90% respectively. A novel homology model, comprehensive agonist and inhibitor titration experiments, and AHR localization studies were consistent with competitive antagonism and blockade of nuclear translocation as the primary mechanism of action. CB7993113 (IC50 3.3 × 10(-7) M) effectively reduced invasion of human breast cancer cells in three-dimensional cultures and blocked tumor cell migration in two-dimensional cultures without significantly affecting cell viability or proliferation. Finally, CB7993113 effectively inhibited the bone marrow ablative effects of 7,12-dimethylbenz[a]anthracene in vivo, demonstrating drug absorption and tissue distribution leading to pharmacological efficacy. These experiments suggest that AHR antagonists such as CB7993113 may represent a new class of targeted therapeutics for immunomodulation and/or cancer therapy.

Activation of JNK1/2 and p38 MAPK signaling pathways promotes enterovirus 71 infection in immature dendritic cells

Background

c-Jun NH₂-terminal kinase/stress-activated kinase (JNK/SAPK) and the p38 mitogen-activated protein kinase (p38 MAPK) are important components of cellular signal transduction pathways, which have been reported to be involved in viral replication. However, little is known about JNK1/2 and p38 MAPK signaling pathways in enterovirus 71 (EV71)-infected immature dendritic cells (iDCs). Thus, iDCs were induced from peripheral blood mononuclear cells (PBMC) and performed to explore the expressions and phosphorylation of molecules in the two signaling pathways as well as secretions of inflammatory cytokines and interferons during EV71 replication.

Results

We showed that EV71 infection could activate both JNK1/2 and p38 MAPK in iDCs and phosphorylate their downstream transcription factors c-Fos and c-Jun, which further promoted the production of IL-2, IL-6, IL-10, and TNF-α. Moreover, EV71 infection also increased the release of IFN-β and IL-12 p40. Pretreatment of iDCs with SP600125 and SB203580 (20 μM) could severely impair viral replication and its induced phosphorylation of JNK1/2,p38 MAPK, c-Fos and c-Jun. In addition, treatment of EV71-infected iDCs with SP600125 and SB203580 could inhibit secretions of IL-6, IL-10 and TNF-α.

Conclusion

JNK1/2 and p38 MAPK signaling pathways are beneficial to EV71 infection and positively regulate secretions of inflammatory cytokines in iDCs.

MLK3 regulates fMLP-stimulated neutrophil motility

INTRODUCTION

Mixed lineage kinase 3 (MLK3) is part of the intracellular regulatory system that connects extracellular cytokine or mitogen signals received through G-protein coupled receptors to changes in gene expression. MLK3 activation stimulates motility of epithelial cells and epithelial-derived tumor cells, but its role in mediating the migration of other cell types remains unknown. Since neutrophils play a crucial role in innate immunity and contribute to the pathogenesis of several diseases, we therefore examined whether MLK3 might regulate the motility of mouse neutrophils responding to a chemotactic stimulus, the model bacterial chemoattractant fMLP.

METHODS

The expression of Mlk3 in mouse neutrophils was determined by immunocytochemistry and by RT-PCR. In vitro chemotaxis in a gradient of fMLP, fMLP-stimulated random motility, fMLP-stimulated F-actin formation were measured by direct microscopic observation using neutrophils pre-treated with a novel small molecule inhibitor of MLK3 (URMC099) or neutrophils obtained from Mlk3-/- mice. In vivo effects of MLK3 inhibition were measured by counting the fMLP-induced accumulation of neutrophils in the peritoneum following pre-treatment with URMC099 in wild-type C57Bl/6 or mutant Mlk3-/- mice.

RESULTS

The expression of Mlk3 mRNA and protein was observed in neutrophils purified from wild-type C57Bl/6 mice but not in neutrophils from mutant Mlk3-/- mice. Chemotaxis by wild-type neutrophils induced by a gradient of fMLP was reduced by pre-treatment with URMC099. Neutrophils from C57Bl/6 mice pretreated with URMC099 and neutrophils from Mlk3-/- mice moved far less upon fMLP-stimulation and did not form F-actin as readily as untreated neutrophils from C57Bl/6 controls. In vivo recruitment of neutrophils into the peritoneum by fMLP was significantly reduced in wild-type mice treated with URMC099, as well as in untreated Mlk3-/- mice-thereby confirming the role of MLK3 in neutrophil migration.

CONCLUSIONS

Mlk3 mRNA is expressed in murine neutrophils. Genetic or pharmacologic inhibition of MLK3 blocks fMLP-mediated motility of neutrophils both in vitro and in vivo, suggesting that MLK3 may be a therapeutic target in human diseases characterized by exuberant neutrophil migration.

Mechanism of interleukin-1β-induced proliferation in rat hepatic stellate cells from different levels of signal transduction

Hepatic stellate cells (HSCs) are the major producers of collagen in the liver. Their conversion from resting cells to proliferative, contractile, and activated cells is a critical step leading to liver fibrosis that is characterized by the deposition of excessive extracellular matrix. Interleukin-1 (IL-1) may play a role in maintaining HSC in a proliferative state that is responsible for hepatic fibrogenesis. The aim of this study was to study the roles of the IL-1 type I receptor (IL-1R1), c-Jun N-terminal kinase (JNK), and activation protein-1 (AP-1) in IL-1β-mediated proliferation in rat HSCs. We showed that IL-1β can upregulate proliferation in rat HSCs; however, inhibition of the JNK pathway could inhibit HSCs proliferation. Furthermore, IL-1β activated IL-1R1 expression, the JNK signaling pathway, and AP-1 activity in a time-dependent manner in rat HSCs. These data demonstrate that IL-1β could promote the proliferation of rat HSCs and that the IL-1R1, JNK, and AP-1 pathways were involved in this process. In summary, IL-1β-induced proliferation is possibly mediated by the IL-1R1, JNK, and AP-1 pathways in rat HSCs. Therefore, drugs that block these pathways may inhibit the proliferation of HSCs and suppress liver fibrosis.

The tobacco smoke component, acrolein, suppresses innate macrophage responses by direct alkylation of c-Jun N-terminal kinase

The respiratory innate immune system is often compromised by tobacco smoke exposure, and previous studies have indicated that acrolein, a reactive electrophile in tobacco smoke, may contribute to the immunosuppressive effects of smoking. Exposure of mice to acrolein at concentrations similar to those in cigarette smoke (5 ppm, 4 h) significantly suppressed alveolar macrophage responses to bacterial LPS, indicated by reduced induction of nitric oxide synthase 2, TNF-α, and IL-12p40. Mechanistic studies with bone marrow-derived macrophages or MH-S macrophages demonstrated that acrolein (1-30 μM) attenuated these LPS-mediated innate responses in association with depletion of cellular glutathione, although glutathione depletion itself was not fully responsible for these immunosuppressive effects. Inhibitory actions of acrolein were most prominent after acute exposure (<2 h), indicating the involvement of direct and reversible interactions of acrolein with critical signaling pathways. Among the key signaling pathways involved in innate macrophage responses, acrolein marginally affected LPS-mediated activation of nuclear factor (NF)-κB, and significantly suppressed phosphorylation of c-Jun N-terminal kinase (JNK) and activation of c-Jun. Using biotin hydrazide labeling, NF-κB RelA and p50, as well as JNK2, a critical mediator of innate macrophage responses, were revealed as direct targets for alkylation by acrolein. Mass spectrometry analysis of acrolein-modified recombinant JNK2 indicated adduction to Cys(41) and Cys(177), putative important sites involved in mitogen-activated protein kinase (MAPK) kinase (MEK) binding and JNK2 phosphorylation. Our findings indicate that direct alkylation of JNK2 by electrophiles, such as acrolein, may be a prominent and hitherto unrecognized mechanism in their immunosuppressive effects, and may be a major factor in smoking-induced effects on the immune system.

Toxoplasma gondii triggers release of human and mouse neutrophil extracellular traps

Neutrophils have recently been shown to release DNA-based extracellular traps that contribute to microbicidal killing and have also been implicated in autoimmunity. The role of neutrophil extracellular trap (NET) formation in the host response to nonbacterial pathogens has received much less attention. Here, we show that the protozoan pathogen Toxoplasma gondii elicits the production of NETs from human and mouse neutrophils. Tachyzoites of each of the three major parasite strain types were efficiently entrapped within NETs, resulting in decreased parasite viability. We also show that Toxoplasma activates a MEK-extracellular signal-regulated kinase (ERK) pathway in neutrophils and that the inhibition of this pathway leads to decreased NET formation. To determine if Toxoplasma induced NET formation in vivo, we employed a mouse intranasal infection model. We found that the administration of tachyzoites by this route induced a rapid tissue recruitment of neutrophils with evidence of extracellular DNA release. Taken together, these data indicate a role for NETs in the host innate response to protozoan infection. We propose that NET formation limits infection by direct microbicidal effects on Toxoplasma as well as by interfering with the ability of the parasite to invade target host cells.

Toxoplasma gondii induces B7-2 expression through activation of JNK signal transduction

Toxoplasma gondii is a globally distributed parasite pathogen that infects virtually all warm-blooded animals. A hallmark of immunity to acute infection is the production of gamma interferon (IFN-γ) and interleukin-12 (IL-12), followed by a protective T cell response that is critical for parasite control. Naïve T cell activation requires both T-cell receptor (TCR) stimulation and the engagement of costimulatory receptors. Because of their important function in activating T cells, the expression of costimulatory ligands is believed to be under tight control. The molecular mechanisms governing their induction during microbial stimulation, however, are not well understood. We found that all three strains of T. gondii (types I, II, and III) upregulated the expression of B7-2, but not B7-1, on the surface of mouse bone marrow-derived macrophages. Additionally, intraperitoneal infection of mice with green fluorescent protein (GFP)-expressing parasites resulted in enhanced B7-2 levels specifically on infected, GFP(+) CD11b(+) cells. B7-2 induction occurred at the transcript level, required active parasite invasion, and was not dependent on MyD88 or TRIF. Functional assays demonstrated that T. gondii-infected macrophages stimulated naïve T cell proliferation in a B7-2-dependent manner. Genome-wide transcriptional analysis comparing infected and uninfected macrophages revealed the activation of mitogen-activated protein kinase (MAPK) signaling in infected cells. Using specific inhibitors against MAPKs, we determined that parasite-induced B7-2 is dependent on Jun N-terminal protein kinase (JNK) but not extracellular signal-regulated kinase (ERK) or p38 signaling. We also observed that T. gondii-induced B7-2 expression on human peripheral blood monocytes is dependent on JNK signaling, indicating that a common mechanism of B7-2 regulation by T. gondii may exist in both humans and mice.

JNK-1 deficiency limits macrophage-mediated antigen-induced arthritis

OBJECTIVE

To elucidate the nonredundant roles of JNK-1 and JNK-2 in antigen-induced arthritis (AIA).

METHODS

Mice that were genetically disrupted in Jnk1 or Jnk2 were primed by injection of methylated bovine serum albumin (mBSA) in Freund's complete adjuvant and then challenged on day 21 by intraarticular injection of mBSA into the right knee. Bone marrow chimeras were generated and similarly treated. Joints were harvested and prepared for histologic assessment. T cell responses were verified by cytokine and proliferation responses, and relative immunoglobulin responses were measured by enzyme-linked immunosorbent assay. Cytokine messenger RNA expression levels were measured by quantitative polymerase chain reaction analysis. Thioglycollate-elicited and zymosan A-elicited macrophage recruitment was tested in vivo, and cell migration was tested in vitro. The peptide inhibitor D-JNKi was injected daily starting 4 days after intraarticular injection of mBSA into wild-type (WT) mice, and inflammation was scored histologically.

RESULTS

JNK-1-deficient, but not JNK-2-deficient, mice had a reduction in inflammatory cell infiltration and joint damage. This effect was primarily restricted to hematopoietic cells, but B and T cell responses were preserved in mBSA-injected mice. JNK-1-deficient macrophages produced cytokines and chemokines at a level comparable to that in their WT counterparts. However, macrophage migration was impaired in vivo and in vitro. Targeting JNK with the peptide inhibitor D-JNKi dramatically reduced inflammation and joint destruction in WT mice.

CONCLUSION

AIA is dependent on JNK-1, but not JNK-2. JNK-1 is a promising molecular target for reducing autoimmune inflammation, since its inhibition impairs macrophage migration.

Mouse neutrophils are professional antigen-presenting cells programmed to instruct Th1 and Th17 T-cell differentiation

Neutrophils play a major role in the innate immune system and are normally considered to be short-lived effector cells that exert anti-microbial activity and sometimes immunopathology. Here, we show that these cells possess an additional function as professional antigen-presenting cells capable of priming a T(h)1- and T(h)17-acquired immune response. Using flow cytometry, fluorescence microscopy and western blotting, we show that mouse neutrophils express MHC class II and co-stimulatory molecules CD80 and CD86 after T-cell co-incubation. Neutrophils pulsed with ovalbumin (OVA) process and present peptide antigen to OVA-specific T cells in an MHC class II-dependent manner. Importantly, we demonstrate that neutrophils can prime antigen-specific T(h)1 and T(h)17 immune responses even without the addition of exogenous cytokines to cell cultures.

Chemokine transcripts as targets of the RNA-binding protein HuR in human airway epithelium

HuR is a regulator of mRNA turnover or translation of inflammatory genes through binding to adenylate-uridylate-rich elements and related motifs present in the 3'untranslated region (UTR) of mRNAs. We postulate that HuR critically regulates the epithelial response by associating with multiple ARE-bearing, functionally related inflammatory transcripts. We aimed to identify HuR targets in the human airway epithelial cell line BEAS-2B challenged with TNF-α plus IFN-γ, a strong stimulus for inflammatory epithelial responses. Ribonucleoprotein complexes from resting and cytokine-treated cells were immunoprecipitated using anti-HuR and isotype-control Ab, and eluted mRNAs were reverse-transcribed and hybridized to an inflammatory-focused gene array. The chemokines CCL2, CCL8, CXCL1, and CXCL2 ranked highest among 27 signaling and inflammatory genes significantly enriched in the HuR RNP-IP from stimulated cells over the control immunoprecipitation. Among these, 20 displayed published HuR binding motifs. Association of HuR with the four endogenous chemokine mRNAs was validated by single-gene ribonucleoprotein-immunoprecipitation and shown to be 3'UTR-dependent by biotin pull-down assay. Cytokine treatment increased mRNA stability only for CCL2 and CCL8, and transient silencing and overexpression of HuR affected only CCL2 and CCL8 expression in primary and transformed epithelial cells. Cytokine-induced CCL2 mRNA was predominantly cytoplasmic. Conversely, CXCL1 mRNA remained mostly nuclear and unaffected, as CXCL2, by changes in HuR levels. Increase in cytoplasmic HuR and HuR target expression partially relied on the inhibition of AMP-dependent kinase, a negative regulator of HuR nucleocytoplasmic shuttling. HuR-mediated regulation in airway epithelium appears broader than previously appreciated, coordinating numerous inflammatory genes through multiple posttranscriptional mechanisms.

JNK1 controls mast cell degranulation and IL-1{beta} production in inflammatory arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease marked by bone and cartilage destruction. Current biologic therapies are beneficial in only a portion of patients; hence small molecules targeting key pathogenic signaling cascades represent alternative therapeutic strategies. Here we show that c-Jun N-terminal kinase (JNK) 1, but not JNK2, is critical for joint swelling and destruction in a serum transfer model of arthritis. The proinflammatory function of JNK1 requires bone marrow-derived cells, particularly mast cells. Without JNK1, mast cells fail to degranulate efficiently and release less IL-1β after stimulation via Fcγ receptors (FcγRs). Pharmacologic JNK inhibition effectively prevents arthritis onset and abrogates joint swelling in established disease. Hence, JNK1 controls mast cell degranulation and FcγR-triggered IL-1β production, in addition to regulating cytokine and matrix metalloproteinase biosynthesis, and is an attractive therapeutic target in inflammatory arthritis.

Absence of mitogen-activated protein kinase family member c-Jun N-terminal kinase-2 enhances resistance to Toxoplasma gondii

The function of mitogen-activated protein kinase (MAPK) family member c-Jun N-terminal kinase (JNK)-2 in resistance and pathology during infection has not been greatly studied. Here, we employed Jnk2(-/-) mice to investigate the role of JNK2 in resistance and immunity during oral infection with the protozoan pathogen Toxoplasma gondii. We found increased host resistance in the absence of JNK2 as determined by lower parasite burden and increased host survival. Lack of JNK2 also correlated with decreased neutrophil recruitment to the intestinal mucosa and less pathology in the small intestine. In the absence of JNK2, IL-12 production was slightly but significantly increased in restimulated splenocyte populations as well as in purified splenic dendritic cell cultures. These results provide evidence that expression of JNK2 plays a role in T. gondii-induced immunopathology, at the same time in promoting susceptibility to this parasitic pathogen.

Regulation of the immune response by stress-activated protein kinases

Activation of immune cells to mediate an immune response is often triggered by potential 'danger' or 'stress' stimuli that the organism receives. Within the mitogen-activated protein kinases (MAPKs) family, the stress-activated protein kinase (SAPK) group was defined as group of kinases that activated by stimuli that cause cell stress. In the immune cells, SAPKs are activated by antigen receptors (B- or T-cell receptors), Toll-like receptors, cytokine receptors, and physical-chemical changes in the environment among other stimuli. The SAPKs are established to be important mediators of intracellular signaling during adaptive and innate immune responses. Here we summarize what is currently known about the role of two sub-groups of SAPKs - c-Jun NH(2)-terminal kinase and p38 MAPK-in the function of specific components of the immune system and the overall contribution to the immune response.

TLR adaptor MyD88 is essential for pathogen control during oral toxoplasma gondii infection but not adaptive immunity induced by a vaccine strain of the parasite

TLR adaptor MyD88 activation is important in host resistance to Toxoplasma gondii during i.p. infection, but the function of this signaling pathway during oral infection, in which mucosal immunity assumes a predominant role, has not been examined. In this study, we show that MyD88(-/-) mice fail to control the parasite and succumb within 2 wk of oral infection. Early during infection, T cell IFN-gamma production, recruitment of neutrophils and induction of p47 GTPase IGTP (Irgm3) in the intestinal mucosa were dependent upon functional MyD88. Unexpectedly, these responses were MyD88-independent later during acute infection. In particular, CD4(+) T cell IFN-gamma reached normal levels independently of MyD88, despite continued absence of IL-12 in these animals. The i.p. vaccination of MyD88(-/-) mice with an avirulent T. gondii uracil auxotroph elicited robust IFN-gamma responses and protective immunity to challenge with a high virulence T. gondii strain. Our results demonstrate that MyD88 is required to control Toxoplasma infection, but that the parasite can trigger adaptive immunity without the need for this TLR adaptor molecule.

The immunobiology of the innate response to Toxoplasma gondii

Toxoplasma gondii is a unique intracellular parasite. It can infect a variety of cells in virtually all warm-blooded animals. It has a worldwide distribution and, overall, around one-third of people are seropositive for the parasite, with essentially the entire human population being at risk of infection. For most people, T. gondii causes asymptomatic infection but the parasite can cause serious disease in the immunocompromised and, if contracted for the first time during pregnancy, can cause spontaneous abortion or congenital defects, which have a substantial emotional, social and economic impact. Toxoplasma gondii provokes one of the most potent innate, pro-inflammatory responses of all infectious disease agents. It is also a supreme manipulator of the immune response so that innate immunity to T. gondii is a delicate balance between the parasite and its host involving a coordinated series of cellular interactions involving enterocytes, neutrophils, dendritic cells, macrophages and natural killer cells. Underpinning these interactions is the regulation of complex molecular reactions involving Toll-like receptors, activation of signalling pathways, cytokine production and activation of anti-microbial effector mechanisms including generation of reactive nitrogen and oxygen intermediates.