Role of the tumor necrosis factor receptor 2 (TNFR2) in cerebral malaria in mice

Experimental Models to Study the Pathogenesis of Malaria-Associated Acute Respiratory Distress Syndrome

Malaria-associated acute respiratory distress syndrome (MA-ARDS) is increasingly gaining recognition as a severe malaria complication because of poor prognostic outcomes, high lethality rate, and limited therapeutic interventions. Unfortunately, invasive clinical studies are challenging to conduct and yields insufficient mechanistic insights. These limitations have led to the development of suitable MA-ARDS experimental mouse models. In patients and mice, MA-ARDS is characterized by edematous lung, along with marked infiltration of inflammatory cells and damage of the alveolar-capillary barriers. Although, the pathogenic pathways have yet to be fully understood, the use of different experimental mouse models is fundamental in the identification of mediators of pulmonary vascular damage. In this review, we discuss the current knowledge on endothelial activation, leukocyte recruitment, leukocyte induced-endothelial dysfunction, and other important findings, to better understand the pathogenesis pathways leading to endothelial pulmonary barrier lesions and increased vascular permeability. We also discuss how the advances in imaging techniques can contribute to a better understanding of the lung lesions induced during MA-ARDS, and how it could aid to monitor MA-ARDS severity.

Cerebral Malaria: Current Clinical and Immunological Aspects

This review focuses on current clinical and immunological aspects of cerebral malaria induced by Plasmodium falciparum infection. Albeit many issues concerning the inflammatory responses remain unresolved and need further investigations, current knowledge of the underlying molecular mechanisms is highlighted. Furthermore, and in the light of significant limitations in preventative diagnosis and treatment of cerebral malaria, this review mainly discusses our understanding of immune mechanisms in the light of the most recent research findings. Remarkably, the newly proposed CD8+ T cell-driven pathophysiological aspects within the central nervous system are summarized, giving first rational insights into encouraging studies with immune-modulating adjunctive therapies that protect from symptomatic cerebral participation of Plasmodium falciparum infection.

High mobility group box-1 (HMGB-1) and its receptors in the pathogenesis of malaria-associated acute lung injury/acute respiratory distress syndrome in a mouse model

The DNA-binding protein high mobility group box-1 (HMGB-1) mediates proinflammatory cytokines that contribute to acute lung injury (ALI). Although ALI is a frequent complication of malaria infection, the contribution of HMGB-1 and its receptors to the pathogenesis of malaria-associated ALI/acute respiratory distress syndrome (MA-ALI/ARDS) has not been investigated in a mouse model. Here, the malaria-infected mice were divided into two groups according to lung injury score: the ALI/ARDS and non-ALI/ARDS groups. The expression of HMGB-1 and its receptors (RAGE, TLR-2 and TLR-4) in lung tissues was investigated by using immunohistochemical staining and real-time polymerase chain reaction (PCR). Additionally, HMGB-1 and proinflammatory cytokine (TNF-α, IFN-γ, IL-1 and IL-6) levels in plasma and lung tissues were quantified by using enzyme-linked immunosorbent assays. Cellular expression of both HMGB-1 and its receptors (RAGE, TLR-2 and TLR-4) was significantly increased in the lung tissues of the ALI/ARDS group compared with those in the non-ALI/ARDS and control groups. The levels of HMGB-1, TNF-α, IFN-γ, IL-1 and IL-6 were significantly increased in both plasma and lung tissues of the ALI/ARDS group compared with those in the non-ALI/ARDS and control groups, which were similar to the results obtained by real-time PCR. Increased mRNA expression of RAGE, TLR-2 and TLR-4 was found in the lung tissues of the ALI/ARDS group. Furthermore, the plasma HMGB-1 level was positively correlated with TLR-4 mRNA expression in the ALI/ARDS group. HMGB-1 levels were significantly increased in plasma and lung tissues of MA-ALI/ARDS mice and were related to the upregulated expression of HMGB-1 and proinflammatory cytokines. In conclusion, this study demonstrates that HMGB-1 is an important mediator of MA-ALI/ARDS pathogenesis and may represent a target for therapeutic malaria interventions with ALI/ARDS.

The immunological balance between host and parasite in malaria

Coevolution of humans and malaria parasites has generated an intricate balance between the immune system of the host and virulence factors of the parasite, equilibrating maximal parasite transmission with limited host damage. Focusing on the blood stage of the disease, we discuss how the balance between anti-parasite immunity versus immunomodulatory and evasion mechanisms of the parasite may result in parasite clearance or chronic infection without major symptoms, whereas imbalances characterized by excessive parasite growth, exaggerated immune reactions or a combination of both cause severe pathology and death, which is detrimental for both parasite and host. A thorough understanding of the immunological balance of malaria and its relation to other physiological balances in the body is of crucial importance for developing effective interventions to reduce malaria-related morbidity and to diminish fatal outcomes due to severe complications. Therefore, we discuss in this review the detailed mechanisms of anti-malarial immunity, parasite virulence factors including immune evasion mechanisms and pathogenesis. Furthermore, we propose a comprehensive classification of malaria complications according to the different types of imbalances.

Myeloid expression of the AP-1 transcription factor JUNB modulates outcomes of type 1 and type 2 parasitic infections

Activation of macrophages is a key step in the initiation of immune responses, but the transcriptional mechanisms governing macrophage activation during infection are not fully understood. It was recently shown that the AP-1 family transcription factor JUNB positively regulates macrophage activation in response to Toll-like receptor agonists that promote classical or M1 polarization, as well as to the cytokine interleukin-4 (IL-4), which elicits an alternatively activated or M2 phenotype. However, a role for JUNB in macrophage activation has never been demonstrated in vivo. Here, to dissect the role of JUNB in macrophage activation in a physiological setting, mice lacking JUNB specifically in myeloid cells were tested in two infection models: experimental cerebral malaria, which elicits a pathological type 1 immune response, and helminth infection, in which type 2 responses are protective. Myeloid-restricted deletion of Junb reduced type 1 immune activation, which was associated with reduced cerebral pathology and improved survival during infection with Plasmodium berghei. Myeloid JUNB deficiency also compromised type 2 activation during infection with the hookworm Nippostrongylus brasiliensis, leading to diminished cytokine production and eosinophil recruitment and increased parasite burden. These results demonstrate that JUNB in myeloid cells shapes host responses and outcomes during type 1 and type 2 infections.

Platelet interactions with viruses and parasites

While the interactions between Gram-positive bacteria and platelets have been well characterized, there is a paucity of data on the interaction between other pathogens and platelets. However, thrombocytopenia is a common feature with many infections especially viral hemorrhagic fever. The little available data on these interactions indicate a similarity with bacteria-platelet interactions with receptors such as FcγRIIa and Toll-Like Receptors (TLR) playing key roles with many pathogens. This review summarizes the known interactions between platelets and pathogens such as viruses, fungi and parasites.

The systemic pathology of cerebral malaria in African children

Pediatric cerebral malaria carries a high mortality rate in sub-Saharan Africa. We present our systematic analysis of the descriptive and quantitative histopathology of all organs sampled from a series of 103 autopsies performed between 1996 and 2010 in Blantyre, Malawi on pediatric cerebral malaria patients and control patients (without coma, or without malaria infection) who were clinically well characterized prior to death. We found brain swelling in all cerebral malaria patients and the majority of controls. The histopathology in patients with sequestration of parasites in the brain demonstrated two patterns: (a) the “classic” appearance (i.e., ring hemorrhages, dense sequestration, and extra-erythrocytic pigment) which was associated with evidence of systemic activation of coagulation and (b) the “sequestration only” appearance associated with shorter duration of illness and higher total burden of parasites in all organs including the spleen. Sequestration of parasites was most intense in the gastrointestinal tract in all parasitemic patients (those with cerebral malarial and those without).

Transdermal glyceryl trinitrate as an effective adjunctive treatment with artemether for late-stage experimental cerebral malaria

Cerebral malaria (CM) is associated with low nitric oxide (NO) bioavailability, cerebrovascular constriction, occlusion, and hypoperfusion. Administration of exogenous NO partially prevents the neurological syndrome and associated vascular pathology in an experimental CM (ECM) mouse model. In this study, we evaluated the effects of transdermal glyceryl trinitrate in preventing ECM and, in combination with artemether, rescuing late-stage ECM mice from mortality. The glyceryl trinitrate and/or artemether effect on survival and clinical recovery was evaluated in C57BL/6 mice infected with P. berghei ANKA. NO synthase (NOS) expression in mouse brain was determined by Western blots. Mean arterial pressure (MAP) and pial arteriolar diameter were monitored using a tail-cuff blood pressure system and a cranial window preparation, respectively. Preventative administration of glyceryl trinitrate at 0.025 mg/h decreased ECM mortality from 67 to 11% and downregulated inducible NOS expression in the brain. When administered as adjunctive rescue therapy with artemether, glyceryl trinitrate increased survival from 47 to 79%. The adjunctive therapy caused a sustained reversal of pial arteriolar vasoconstriction in ECM mice, an effect not observed with artemether alone. Glyceryl trinitrate induced a 13% decrease in MAP in uninfected mice but did not further affect MAP in hypotensive ECM mice. Glyceryl trinitrate, when combined with artemether, was an effective adjunctive rescue treatment for ECM. This treatment ameliorated pial arteriolar vasospasm and did not significantly affect MAP. These results indicate that transdermal glyceryl trinitrate has potential to be considered as a candidate for adjunctive therapy for CM.

Pathogenesis of malaria-associated acute respiratory distress syndrome

Malaria-associated acute respiratory distress syndrome (MA-ARDS) is an increasingly reported, often lethal, and incompletely understood complication of malaria. We discuss and compare the pathogenesis of MA-ARDS in patients and in different murine models, including recent models without cerebral involvement, and summarize the roles of different leukocyte subclasses, adhesion molecules, cytokines, and chemokines. In patients as well as in mice, severe edema and impaired gas exchange are associated with abundant inflammatory infiltrates consisting of mainly mononuclear cells and parasite sequestration, and the pathogenesis appears different from cerebral malaria (CM). Experimental anti-inflammatory interventions are successful in mice and remain to be validated in patients.

Peroxisome proliferator activating receptor (PPAR) in cerebral malaria (CM): a novel target for an additional therapy

Cerebral malaria (CM) is a global life-threatening complication of Plasmodium infection and represents a major cause of morbidity and mortality among severe forms of malaria. Despite developing knowledge in understanding mechanisms of pathogenesis, the current anti-malarial agents are not sufficient due to drug resistance and various adverse effects. Therefore, there is an urgent need for the novel target and additional therapy. Recently, peroxisome proliferator-activated receptor (PPAR) a nuclear receptors (NR) and agonists of its isoforms (PPARγ, PPARα and PPARβ/δ) have been demonstrated to exhibit anti-inflammatory and immunomodulatory properties, which are driven to a new approach of research on inflammatory diseases. Although many studies on PPARs have confirmed their diverse biological role, there is a lack of knowledge of its therapeutic use in CM. The major objective of this review is to explore the possible experimental studies to link these two areas of research. We focus on the data describing the beneficial effects of this receptor in inflammation, which is observed as a basic pathology in CM. In conclusion, PPARs could be a novel target in treating inflammatory diseases, and continued work with the available and additional agonists screened from various sources may result in a potential new treatment for CM.

Mice lacking both TNF and IL-1 receptors exhibit reduced lung inflammation and delay in onset of death following infection with a highly virulent H5N1 virus

BACKGROUND

Highly pathogenic avian influenza viruses of the H5N1 subtype continue to cross the species barrier to infect humans and cause severe disease. It has been suggested that an exaggerated immune response contributes to the pathogenesis of H5N1 virus infection in mammals. In particular, H5N1 virus infections are associated with a high expression of the proinflammatory cytokines, including interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-α).

METHODS

We investigated the compounding affects of both cytokines on the outcome of H5N1 virus disease by using triple mutant mice deficient in 3 signaling receptors, TNF-R1, TNF-R2, and IL-1-RI.

RESULTS

Triple mutant mice exhibited reduced morbidity and a significant delay in mortality following lethal challenge with a lethal H5N1 virus, whereas no such differences were observed with the less virulent A/PR/8/34 (H1N1) virus. H5N1-infected triple mutant mice displayed diminished cytokine production in lung tissue and a quantifiable decrease of macrophages and neutrophils in the lungs postinfection. Moreover, morphometric analysis of airway sections revealed less extensive inflammation in H5N1-infected triple mutant mice, compared with infected wild-type mice.

CONCLUSIONS

The combined signaling from the TNF or IL-1 receptors promotes maximal lung inflammation that may contribute to the severity of disease caused by H5N1 virus infection.

Microbial induction of vascular pathology in the CNS

The central nervous system (CNS) is a finely tuned organ that participates in nearly every aspect of our day-to-day function. Neurons lie at the core of this functional unit and maintain an active dialogue with one another as well as their fellow CNS residents (e.g. astrocytes, oligodendrocytes, microglia). Because of this complex dialogue, it is essential that the CNS milieu be tightly regulated in order to permit uninterrupted and efficient neural chemistry. This is accomplished in part by anatomical barriers that segregate vascular components from the cerebral spinal fluid (CSF) and brain parenchyma. These barriers impede entry of noxious materials and enable the CNS to maintain requisite protein and ionic balances for constant electrochemical signaling. Under homeostatic conditions, the CNS is protected by the presence of specialized endothelium/epithelium, the blood brain barrier (BBB), and the blood-CSF barrier. However, following CNS infection these protective barriers can be comprised, sometimes resulting in severe neurological complications triggered by an imbalance or blockage of neural chemistry. In some instances, these disruptions are severe enough to be fatal. This review focuses on a selection of microbes (both viruses and parasites) that compromise vascular barriers and induce neurological complications upon gaining access to the CNS. Emphasis is placed on CNS diseases that result from a pathogenic interplay between host immune defenses and the invading microbe.

The role of platelets in the pathogenesis of cerebral malaria

Malaria is a major cause of morbidity and mortality in the developing world and cerebral malaria is responsible for the majority of malaria-associated deaths. There is a strong association between thrombocytopenia and outcome in malaria, suggesting a role for platelets in the pathogenesis of malaria. This thrombocytopenia is likely due to platelet activation possibly through an interaction between PfEMP1 on plasmodium and CD36 on platelets. Platelet activation by plasmodium has two potential consequences. It can lead to the formation of micro-aggregates of infected red blood cells and platelets which can occlude blood vessels and it also leads to binding to and activation of the endothelium.

Plasma IP-10, apoptotic and angiogenic factors associated with fatal cerebral malaria in India

Background

Plasmodium falciparum in a subset of patients can lead to cerebral malaria (CM), a major contributor to malaria-associated mortality. Despite treatment, CM mortality can be as high as 30%, while 10% of survivors of the disease may experience short- and long-term neurological complications. The pathogenesis of CM is mediated by alterations in cytokine and chemokine homeostasis, inflammation as well as vascular injury and repair processes although their roles are not fully understood. The hypothesis for this study is that CM-induced changes in inflammatory, apoptotic and angiogenic factors mediate severity of CM and that their identification will enable development of new prognostic markers and adjunctive therapies for preventing CM mortalities.

Methods

Plasma samples (133) were obtained from healthy controls (HC, 25), mild malaria (MM, 48), cerebral malaria survivors (CMS, 48), and cerebral malaria non-survivors (CMNS, 12) at admission to the hospital in Jabalpur, India. Plasma levels of 30 biomarkers ((IL-1β, IL-1ra, IL-2, IL-4, IL-5, IL-6, IL-8, IL-9, IL-10, IL-12 (p70), IL-13, IL-15, IL-17, Eotaxin, FGF basic protein, G-CSF, GM-CSF, IFN-γ, IP-10, MCP-1 (MCAF), MIP-1α, MIP-1β, RANTES, TNF-α, Fas-ligand (Fas-L), soluble Fas (sFas), soluble TNF receptor 1 (sTNF-R1) and soluble TNF receptor 2 (sTNFR-2), PDGF bb and VEGF)) were simultaneously measured in an initial subset of ten samples from each group. Only those biomarkers which showed significant differences in the pilot analysis were chosen for testing on all remaining samples. The results were then compared between the four groups to determine their role in CM severity.

Results

IP-10, sTNF-R2 and sFas were independently associated with increased risk of CM associated mortality. CMNS patients had a significantly lower level of the neuroprotective factor VEGF when compared to other groups (P < 0.0045). The ratios of VEGF to IP-10, sTNF-R2, and sFas distinguished CM survivors from non survivors (P < 0.0001).

Conclusion

The results suggest that plasma levels of IP-10, sTNF-R2 and sFas may be potential biomarkers of CM severity and mortality. VEGF was found to be protective against CM associated mortality and may be considered for adjunctive therapy to improve the treatment outcome in CM patients.

CXCR3 determines strain susceptibility to murine cerebral malaria by mediating T lymphocyte migration toward IFN-gamma-induced chemokines

Cerebral malaria (CM) results from the binding of infected erythrocytes and leukocytes to brain endothelia. The precise mechanisms underlying lymphocyte recruitment and activation in CM remain unclear. Therefore, the expression of various chemokines was quantified in brains of mice infected with Plasmodium berghei ANKA (PbA). Several chemokines attracting monocytes and activated T-lymphocytes were expressed at high levels. Their expression was almost completely abrogated in IFN-gamma ligand and receptor KO mice, indicating that IFN-gamma is an essential chemokine inducer in vivo. Surprisingly, the expression levels of chemokines, IFN-gamma and also adhesion molecules in the brain were not lower in CM-resistant Balb/c and DBA/2 mice compared to CM-sensitive C57BL/6 and DBA/1 mice, although T lymphocyte sequestration in the brain was significantly less in CM-resistant than in CM-sensitive mice. This difference correlated with a higher up-regulation of the CXC chemokine receptor (CXCR)-3 on splenic T cells and a higher chemotactic response to IFN-gamma-inducible protein-10 (IP-10) in C57BL/6 compared to Balb/c mice. In conclusion, parasite-induced IFN-gamma in the brain results in high local expression levels of specific chemokines for monocytes and lymphocytes. The strain-dependent susceptibility to develop CM is more related to the expression of CXCR3 in circulating leukocytes than to the chemokine expression levels in the brain.

Cerebrospinal fluid and serum biomarkers of cerebral malaria mortality in Ghanaian children

Background

Plasmodium falciparum can cause a diffuse encephalopathy known as cerebral malaria (CM), a major contributor to malaria associated mortality. Despite treatment, mortality due to CM can be as high as 30% while 10% of survivors of the disease may experience short- and long-term neurological complications. The pathogenesis of CM and other forms of severe malaria is multi-factorial and appear to involve cytokine and chemokine homeostasis, inflammation and vascular injury/repair. Identification of prognostic markers that can predict CM severity will enable development of better intervention.

Methods

Postmortem serum and cerebrospinal fluid (CSF) samples were obtained within 2–4 hours of death in Ghanaian children dying of CM, severe malarial anemia (SMA), and non-malarial (NM) causes. Serum and CSF levels of 36 different biomarkers (IL-1β, IL-1ra, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-10, IL-12 (p70), IL-13, IL-15, IL-17, Eotaxin, FGF basic protein, CRP, G-CSF, GM-CSF, IFN-γ, TNF-α, IP-10, MCP-1 (MCAF), MIP-1α, MIP-1β, RANTES, SDF-1α, CXCL11 (I-TAC), Fas-ligand [Fas-L], soluble Fas [sFas], sTNF-R1 (p55), sTNF-R2 (p75), MMP-9, TGF-β1, PDGF bb and VEGF) were measured and the results compared between the 3 groups.

Results

After Bonferroni adjustment for other biomarkers, IP-10 was the only serum biomarker independently associated with CM mortality when compared to SMA and NM deaths. Eight CSF biomarkers (IL-1ra, IL-8, IP-10, PDGFbb, MIP-1β, Fas-L, sTNF-R1, and sTNF-R2) were significantly elevated in CM mortality group when compared to SMA and NM deaths. Additionally, CSF IP-10/PDGFbb median ratio was statistically significantly higher in the CM group compared to SMA and NM groups.

Conclusion

The parasite-induced local cerebral dysregulation in the production of IP-10, 1L-8, MIP-1β, PDGFbb, IL-1ra, Fas-L, sTNF-R1, and sTNF-R2 may be involved in CM neuropathology, and their immunoassay may have potential utility in predicting mortality in CM.

Linkage and association analysis of candidate genes for TB and TNFalpha cytokine expression: evidence for association with IFNGR1, IL-10, and TNF receptor 1 genes

Tuberculosis (TB) is a growing public health threat globally and several studies suggest a role of host genetic susceptibility in increased TB risk. As part of a household contact study in Kampala, Uganda, we have taken a unique approach to the study of genetic susceptibility to TB by developing an intermediate phenotype model for TB susceptibility, analyzing levels of tumor necrosis factor-alpha (TNFalpha) in response to culture filtrate as the phenotype. In the present study, we analyzed candidate genes related to TNFalpha regulation and found that interleukin (IL)-10, interferon-gamma receptor 1 (IFNGR1), and TNFalpha receptor 1 (TNFR1) genes were linked and associated to both TB and TNFalpha. We also show that these associations are with progression to active disease and not susceptibility to latent infection. This is the first report of an association between TB and TNFR1 in a human population and our findings for IL-10 and IFNGR1 replicate previous findings. By observing pleiotropic effects on both phenotypes, we show construct validity of our intermediate phenotype model, which enables the characterization of the role of these genetic polymorphisms on TB pathogenesis. This study further illustrates the utility of such a model for disentangling complex traits.

Cell vesiculation and immunopathology: implications in cerebral malaria

Microparticles are plasma membrane fragments that are generated and released under physiological conditions. They are also released when tissue and/or systemic homeostasis is disrupted. These microparticles display different physiological features of the cells from which they originate. They are detected in some pathological conditions, but rarely suspected of participating in the disease's pathogenesis. In the present review, we summarise data about the production of the microparticles, their biological significance and potential role during microorganism-driven processes, especially in cerebral malaria.

Cell- rather than antibody-mediated immunity leads to the development of profound thrombocytopenia during experimental Plasmodium berghei malaria

Experimental malarial thrombocytopenia can reach life-threatening levels and is believed to be due to Abs targeting platelets for destruction by the reticuloendothelial system. However, we report that Abs account for at most 15% of platelet destruction as Plasmodium berghei-infected B cell-deficient mice exhibited profound thrombocytopenia (83%) as did C57BL/6 controls (98%). Further, no significant increase in Abs bound to intact platelets was observed during infection. P. berghei infection can enhance the activity of anti-platelet Abs as indicated by a significantly (p < 0.005) increased thrombocytopenia on day 4 of infection in mice that were administered a low dose anti-CD41 mAb compared with rat IgG1-injected controls. RAG1-/- and CD4- plus CD8-deficient mice were markedly protected from thrombocytopenia (p < 0.005) and malarial pathogenesis. CD8- or TCRgammadelta-deficient mice were not protected from thrombocytopenia and CD4-deficient mice were modestly protected. RAG1-/- mice exhibited significantly (p < 0.05) lower levels of plasma TNF, IFN-gamma, and IL-12 during infection. IFNgamma-/- and IL-12-/- mice exhibited increased survival but similar thrombocytopenia to C57BL/6 controls. Collectively, these data indicate that thrombocytopenia is necessary but not sufficient for malarial pathogenesis and Abs are not the major contributors to malarial thrombocytopenia. Rather, we propose that both CD4+ and CD8+ T cell populations play key roles in malarial thrombocytopenia; a complex bidirectional interaction between cell-mediated immunity and platelets exists during experimental severe malaria that regulates both responses.

Fas has a role in cerebral malaria, but not in proliferation or exclusion of the murine parasite in mice

We examined the susceptibility of murine Fas-deficient mutants to malaria infection in order to investigate the role of Fas in an experimental murine model of cerebral malaria (CM). We infected mice of B6 and CBA wild-type and mutant backgrounds with Plasmodium berghei ANKA. The incidence of CM in the mutant mice (B6-lpr, CBA-lprcg) was decreased by about 50% compared with wild-type control strains at 2 weeks after infection. We did not observe significant differences of parasitemia during a murine malaria infection with nonlethal Plasmodium yoelii 17XNL between wild-type and lymphoproliferative (lpr) mutant mice of C3H and MRL genetic backgrounds, although B6-lpr mice exhibited significantly higher parasitemia than did B6 mice 12 to 18 days after infection. These results suggest Fas has a possible role in CM but may not play a major role in the proliferation or exclusion of a murine malaria parasite in a nonlethal infection.

Review Article: Blood-brain barrier in falciparum malaria*

Plasmodium falciparum malaria is the most important parasitic disease infecting the central nervous system of humans worldwide. The pathogenesis of the neurological complications of falciparum malaria remains unclear. In particular, how do asexual parasites confined to the vascular space of the brain cause neuronal impairment? The evidence for a breakdown in the blood-brain barrier (BBB) is conflicting. In some animal models of malaria, there is evidence of breakdown of the BBB, but the data from humans suggests the BBB is mildly impaired only, with few morphological changes. Whether these changes in the BBB are sufficient to account for the neurological complications remains to be determined.

Inhibition of the Growth ofToxoplasma gondiiin Immature Human Dendritic Cells Is Dependent on the Expression of TNF-α Receptor 2

An effective immunity to Toxoplasma gondii in humans is dependent on the cellular immune response. Toxoplasma can infect and replicate in almost all nucleated cells, and the most important cytokine regulating the growth in humans is IFN-gamma; however, the role of TNF-alpha has to date been largely described to be synergistic. We show that, compared with mature human dendritic cells (mDC), immature human DC (iDC) demonstrate a reduced parasite proliferation when infected with Toxoplasma. This toxoplasmostasis was only present in iDC after 11 days of culture and was not present in DC that had been matured ex vivo using a cytokine mixture (mDC). Spontaneous toxoplasmostatic activity has previously only been described in fresh human monocytes, and the mechanism involved is as yet unclear. We show that, in comparison with an absence of expression in mDC, TNF-R2 is expressed in both iDC and monocytes infected with Toxoplasma, and furthermore, that blocking the TNF-R2 with Abs abrogates the toxoplasmostasis in the iDC. These findings demonstrate a functional role for TNF-R2 in the newly described spontaneous toxoplasmostasis of iDC.

The Proinflammatory Cytokines Tumor Necrosis Factor-α and Interleukin-1 Stimulate Neuropeptide Gene Transcription and Secretion in Adrenochromaffin Cells via Activation of Extracellularly Regulated Kinase 1/2 and p38 Protein Kinases, and Activator Protein-1 Transcription Factors

Immune-autonomic interactions are known to occur at the level of the adrenal medulla, and to be important in immune and stress responses, but the molecular signaling pathways through which cytokines actually affect adrenal chromaffin cell function are unknown. Here, we studied the effects of the proinflammatory cytokines, TNF-alpha and IL-1, on gene transcription and secretion of bioactive neuropeptides, in primary bovine adrenochromaffin cells. TNF-alpha and IL-1 induced a time- and dose-dependent increase in galanin, vasoactive intestinal polypeptide, and secretogranin II mRNA levels. The two cytokines also stimulated the basal as well as depolarization-provoked release of enkephalin and secretoneurin from chromaffin cells. Stimulatory effects of TNF-alpha on neuropeptide gene expression and release appeared to be mediated through the type 2 TNF-alpha receptor, and required activation of ERK 1/2 and p38, but not Janus kinase, MAPKs. In addition, TNF-alpha increased the binding activity of activator protein-1 (AP-1) and stimulated transcription of a reporter gene containing AP-1-responsive elements in chromaffin cells. The AP-1-responsive reporter gene could also be activated through the ERK pathway. These results suggest that neuropeptide biosynthesis in chromaffin cells is regulated by TNF-alpha via an ERK-dependent activation of AP-1-responsive gene elements. Either locally produced or systemic cytokines might regulate biosynthesis and release of neuropeptides in chromaffin cells, integrating the adrenal medulla in the physiological response to inflammation. This study describes, for the first time, a signal transduction pathway activated by TNF-alpha in a major class of neuroendocrine cells that, unlike TNF-alpha signaling in lymphoid cells, employs ERK and p38 rather than Janus kinase and p38 to transmit gene-regulatory signals to the cell nucleus.

Roles for early response cytokines during Escherichia coli pneumonia revealed by mice with combined deficiencies of all signaling receptors for TNF and IL-1

During infection, inflammation is essential for host defense, but it can injure tissues and compromise organ function. TNF-alpha and IL-1 (alpha and beta) are early response cytokines that facilitate inflammation. To determine the roles of these cytokines with overlapping functions, we generated mice deficient in all of the three receptors mediating their effects (TNFR1, TNFR2, and IL-1RI). During Escherichia coli pneumonia, receptor deficiency decreased neutrophil recruitment and edema accumulation to half of the levels observed in wild-type mice. Thus these receptors contributed to maximal responses, but substantial inflammation progressed independently of them. Receptor deficiency compromised antibacterial efficacy for some infectious doses. Decreased ventilation during E. coli pneumonia was not affected by receptor deficiency. However, the loss of lung compliance during pneumonia was substantially attenuated by receptor deficiency. Thus during E. coli pneumonia in mice, the lack of signaling from TNF-alpha and IL-1 decreases inflammation and preserves lung compliance.