Decreased serum levels of TGF-beta in patients with acute Plasmodium falciparum malaria

Role of MyD88-Adaptor-Like (MAL) Gene Polymorphism rs8177374 and Cytokine (IFN-γ, TNF-α, IL-10, TGF-β) Levels in Diverse Malaria Manifestations upon P. falciparum and P. vivax Infections

This study investigated the role of genetic variant rs8177374 in MAL/TIRAP gene in mediating the cytokine levels of IFN-γ, TNF-α, IL-10, and TGF-β in malaria patients due to Plasmodium falciparum or P. vivax infection. The study included human blood samples collected from patients with malaria (n = 228) and healthy controls (n = 226). P. falciparum and P. vivax groups were established based on the causative species of Plasmodium. Malaria samples were divided into mild and severe malaria groups based on the symptoms that appeared in the patients, according to the WHO criteria. In a previous study, we genotyped rs8177374 via allele specific PCR strategy. In this study, cytokine levels were estimated in the blood plasma of rs8177374 genotype samples via Sandwich Enzyme Linked Immunosorbent Assay kits. Increased IFN-γ and TNF-α levels in presence of CC genotype indicates the role of CC genotype in both severe and mild malaria groups. Enhanced IL-10 levels in the CT genotype and mild malaria groups suggest a role of CT genotype and IL-10 in the mild clinical outcomes of malaria. The rs8177374 polymorphism in MAL/TIRAP plays an important role in malaria pathogenesis.

Integrated Analysis of Cytokine Profiles in Malaria Patients Discloses Selective Upregulation of TGF-β1, β3, and IL-9 in Mild Clinical Presentation

The proper control of Plasmodium infection requires a finely balanced immune response. Here, we evaluated the implication of TGF-β1 and TGF-β3 in this process using novel monoclonal antibodies to measure their plasma concentrations in comparison with other cytokines and the expression of FOXP3 mRNA. Plasma cytokine levels were measured in 80 patients with severe anaemic malaria and 186 with a mild presentation using ELISA, and rtPCR was used to measure FOXP3 mRNA expression. While no mature TGF-β isoforms were detected in the plasma, the latent TGF-β1 and TGF-β3 were strongly upregulated in patients with mild malaria and nearly undetected in patients with severe disease. Similar selective upregulation in mild patients was observed for IL-9 and FOXP3 mRNA, while IL-7, IL-10, IL-17, and IL-27, although higher in mild cases, were also detected in severe disease. In contrast, a clearly skewed trend of severe cases towards higher pro-inflammatory (IL-6, IL-13, TNF-α) and Th1 (IFN-γ) responses was observed, which was associated with a higher level of parasitaemia as well as lower IgG and higher IgM responses. Together, these results suggest that the stimulation of regulatory T cells through TGF-β1/TGF-β3 and IL-9 is paramount to an effective and balanced protective immunity in natural human malaria infection.

Transforming Growth Factor-β Concerning Malarial Infection and Severity: A Systematic Review and Meta-Analysis

Transforming growth factor-β (TGF-β) is important in the pathophysiology of malaria, but its role in acute and severe malaria is largely unknown. As a result, this study used a meta-analysis approach to investigate the difference in TGF-β levels between several groups of malaria patients and healthy controls. The systematic review protocol was registered at PROSPERO (ID: CRD42022318864). From inception to 7 March 2022, studies that reported TGF-β levels in patients with uncomplicated and healthy controls and patients with severe and uncomplicated malaria were searched in PubMed, Scopus and Embase. The assessment of the quality of the included studies was conducted according to the Strengthening the Reporting of Observational Studies in Epidemiology guidelines. Qualitative and quantitative syntheses were performed to narratively describe and quantitatively pool the mean difference (MD) in TGF-β levels between uncomplicated malaria and healthy controls, and between severe and uncomplicated malaria, using a random-effects model. A total of 1027 relevant articles were identified, and 13 studies were included for syntheses. The meta-analysis results show 233 patients with uncomplicated malaria and 239 healthy controls. Patients with uncomplicated malaria (233 cases) had lower mean TGF-β levels than healthy controls (239 cases; p < 0.01, pooled MD = −14.72 pg/mL, 95% confidence interval (95% CI) = −20.46 to 8.99 pg/mL, I2 = 98.82%, seven studies). The meta-analysis found no difference in mean TGF-β levels between patients with severe malaria (367 cases) and patients with uncomplicated malaria (180 cases; p = 0.11, pooled MD = −6.07 pg/mL, 95% CI = −13.48 to 1.35 pg/mL, I2 = 97.73%, six studies). The meta-analysis demonstrated decreased TGF-β levels in patients with uncomplicated malaria compared to healthy controls. In addition, no difference in TGF-β levels was found between patients with severe and uncomplicated malaria. More research is needed to determine whether TGF-β levels could be a candidate marker for malarial infection or disease severity.

Mouse Models for Unravelling Immunology of Blood Stage Malaria

Malaria comprises a spectrum of disease syndromes and the immune system is a major participant in malarial disease. This is particularly true in relation to the immune responses elicited against blood stages of Plasmodium-parasites that are responsible for the pathogenesis of infection. Mouse models of malaria are commonly used to dissect the immune mechanisms underlying disease. While no single mouse model of Plasmodium infection completely recapitulates all the features of malaria in humans, collectively the existing models are invaluable for defining the events that lead to the immunopathogenesis of malaria. Here we review the different mouse models of Plasmodium infection that are available, and highlight some of the main contributions these models have made with regards to identifying immune mechanisms of parasite control and the immunopathogenesis of malaria.

Quantitative cytokine level of TNF-α, IFN-γ, IL-10, TGF-β and circulating Epstein-Barr virus DNA load in individuals with acute Malaria due to P. falciparum or P. vivax or double infection in a Malaria endemic region in Indonesia

Plasmodium falciparum Malaria and Epstein-Barr Virus (EBV) infection are risk factors in the development of Burkitt’s lymphoma. In Indonesia, 100% of the population is persistently infected with EBV early in life and at risk of developing EBV-linked cancers. Currently, 10.7 million people in Indonesia are living in Malaria-endemic areas. This cross-sectional study was initiated to investigate how acute Malaria dysregulates immune control over latent EBV infection. Using blood and plasma samples of 68 patients with acute Malaria and 27 healthy controls, we measured the level of parasitemia for each plasmodium type (P. falciparum, P. vivax, and mixed) by microscopy and rapid test. The level of 4 regulatory cytokines was determined by quantitative ELISA and the level of circulating EBV genome by real-time PCR targeting the single copy EBNA-1 sequence. All Plasmodium-infected cases had high-level parasitemia (>1000 parasites/ul blood) except for one case. EBV-DNA levels were significantly more elevated in P. falciparum and P. vivax infections (P<0.05) compared to controls. EBV-DNA levels were not related to age, gender, Malaria symptoms, or plasmodium type. TNF-α and IL-10 levels were increased in Malaria cases versus controls, but IFN-γ and TGF- β levels were comparable between the groups. Only TNF-α levels in P. falciparum cases showed a clear correlation with elevated EBV DNA levels (R² = 0.8915). This is the first study addressing the relation between EBV (re)activation and cytokine responses during acute Malaria, revealing a clear correlation between pro-inflammatory cytokine TNF-α and EBV-DNA levels, specifically in P. falciparum cases, suggesting this cytokine to be key in dysregulating EBV homeostasis during acute P. falciparum Malaria.

Balancing in a black box: Potential immunomodulatory roles for TGF-β signaling during blood-stage malaria

Malarial disease caused by Plasmodium parasites challenges the mammalian immune system with a delicate balancing act. Robust inflammatory responses are required to control parasite replication within red blood cells, which if unchecked, can lead to severe anemia and fatality. However, the same inflammatory response that controls parasite replication is also associated with immunopathology and severe disease, as is exemplified by cerebral malaria. A robust literature has identified critical roles for innate, cellular, and humoral immune responses orchestrated by IFN-γ and T_H1 type responses in controlling blood stage malarial disease. In contrast, TGF-β and IL-10 have been identified as important anti–inflammatory immunomodulators that help to limit inflammation and pathology during malaria. TGF-β is a pleiotropic cytokine, with the ability to exert a wide variety of context-dependent immunomodulatory roles.

The specific mechanisms that allow TGF-β to protect against malarial pathology remain essentially unexplored and offer a promising avenue to dissect the most critical elements of immunomodulation in avoiding severe malaria. Here we discuss potential immunomodulatory roles for TGF-β during malaria in light of recent advances in our understanding of the role of Tregs during blood-stage malaria.

Evolutionarily Selected Overexpression of the Cytokine BAFF Enhances Mucosal Immune Response Against P. falciparum

We have previously shown that a variant of the TNFSF13B gene that we called BAFF-var increases the production of the cytokine BAFF, upregulating humoral immunity and increasing the risk for certain autoimmune diseases. In addition, genetic population signatures revealed that BAFF-var was evolutionarily advantageous, most likely by increasing resistance to malaria infection, which is a prime candidate for selective pressure. To evaluate whether the increased soluble BAFF (sBAFF) production confers protection, we experimentally assessed the role of BAFF-var in response to malaria antigens. Lysates of erythrocytes infected with Plasmodium falciparum (iRBCs) or left uninfected (uRBCs, control) were used to treat peripheral blood mononuclear cells (PBMCs) with distinct BAFF genotypes. The PBMCs purified from BAFF-var donors and treated with iRBCs showed different levels of specific cells, immunoglobulins, and cytokines as compared with BAFF-WT. In particular, a relevant differential effect on mucosal immunity B subpopulations have been observed. These findings point to specific immune cells and molecules through which the evolutionary selected BAFF-var may have improved fitness during P. falciparum infection.

Transcriptional Modulation of the Host Immunity Mediated by Cytokines and Transcriptional Factors in Plasmodium falciparum-Infected Patients of North-East India

Complications due to malaria are caused mostly by host immunological responses. Plasmodium falciparum subverts host immunity by various strategies, including modulation in the host immune responses by regulating cytokines. The transcriptional alterations of major cytokines and immunoregulators were analyzed in this study through gene expression profiling in clinically defined subgroups of P. falciparum patients. Malaria patients were included from Dhalai district hospital of Tripura with uncomplicated malaria (UC) and severe malaria (SM) and healthy controls from endemic and non-endemic areas of India. qPCR gene expression analysis was performed for all factors and they were grouped into three clusters based on their altered expressions. The first cluster was downregulated with an increased parasitic burden which included T-BET, GATA3, EOMES, TGF-β, STAT4, STAT6 and cytokines IFN-γ, IL-12, IL-4, IL-5, and IL-13. RANTES, IL-8, CCR8, and CXCR3 were decreased in the SM group. The second cluster was upregulated with severity and included TNF-α, IL-10, IL-1β and IL-7. PD-1 and BCL6 were increased in the SM group. The third cluster comprised of NF-κB and was not altered. The level of perforin was suppressed while GrB expression was elevated in SM. P. falciparum malaria burden is characterized by the modulation of host immunity via compromization of T cell-mediated responses and suppression of innate immune-regulators.

Transforming growth factor-beta profiles correlate with clinical symptoms and parameters of haemostasis and inflammation in a controlled human malaria infection

BACKGROUND

After a controlled human malaria infection (CHMI), presentation of clinical signs and symptoms and host responses is heterogeneous. Transforming growth factor-beta (TGF-β) is the first serum cytokine that changes in malaria-naïve volunteers after CHMI. We studied a possible relation between TGF-β changes, pro-inflammatory cytokines, activation of haemostasis and endothelial cells and clinical symptoms.

METHODS

A panel of cytokines including TGF-β, and markers of activation of haemostasis and endothelial cells were measured in blood samples of 15 volunteers at baseline before CHMI and during CHMI at day of treatment. The change of the parameters on the day of treatment was examined for a significant alteration during infection.

RESULTS

Nine of 15 volunteers showed a significant decrease in TGF-β compared to baseline, with concomitant increased concentrations of D-dimer (p = 0.012), Von Willebrand factor (p = 0.017), IL-6 (p = 0.012) and IFN-γ (0.028) and a significantly decreased platelet count (p = 0.011). In contrast, 6 of 15 volunteers showed sustained or increased TGF-β concentrations without change in the aforementioned parameters. The sustained responders presented with less moderate and severe clinical symptoms than the negative responders (p = 0.036) and had a higher baseline lymphocyte count (p = 0.026). TGF-β concentrations did not correlate with the parasitaemia on day of treatment.

CONCLUSION

Early decreases of serum TGF-β might function a marker for a pro-inflammatory host response and downstream clinical symptoms and pathology during CHMI.

Genetics of Malaria Inflammatory Responses: A Pathogenesis Perspective

Despite significant progress in combating malaria in recent years the burden of severe disease and death due to Plasmodium infections remains a global public health concern. Only a fraction of infected people develops severe clinical syndromes motivating a longstanding search for genetic determinants of malaria severity. Strong genetic effects have been repeatedly ascribed to mutations and allelic variants of proteins expressed in red blood cells but the role of inflammatory response genes in disease pathogenesis has been difficult to discern. We revisited genetic evidence provided by inflammatory response genes that have been repeatedly associated to malaria, namely TNF, NOS2, IFNAR1, HMOX1, TLRs, CD36, and CD40LG. This highlighted specific genetic variants having opposing roles in the development of distinct malaria clinical outcomes and unveiled diverse levels of genetic heterogeneity that shaped the complex association landscape of inflammatory response genes with malaria. However, scrutinizing genetic effects of individual variants corroborates a pathogenesis model where pro-inflammatory genetic variants acting in early infection stages contribute to resolve infection but at later stages confer increased vulnerability to severe organ dysfunction driven by tissue inflammation. Human genetics studies are an invaluable tool to find genes and molecular pathways involved in the inflammatory response to malaria but their precise roles in disease pathogenesis are still unexploited. Genome editing in malaria experimental models and novel genotyping-by-sequencing techniques are promising approaches to delineate the relevance of inflammatory response gene variants in the natural history of infection thereby will offer new rational angles on adjuvant therapeutics for prevention and clinical management of severe malaria.

Characterization of Plasmodium berghei Homologues of T-cell Immunomodulatory Protein as a New Potential Candidate for Protecting against Experimental Cerebral Malaria

The pathogenesis of cerebral malaria is biologically complex and involves multi-factorial mechanisms such as microvascular congestion, immunopathology by the pro-inflammatory cytokine and endothelial dysfunction. Recent data have suggested that a pleiotropic T-cell immunomodulatory protein (TIP) could effectively mediate inflammatory cytokines of mammalian immune response against acute graft-versus-host disease in animal models. In this study, we identified a conserved homologue of TIP in Plasmodium berghei (PbTIP) as a membrane protein in Plasmodium asexual stage. Compared with PBS control group, the pathology of experimental cerebral malaria (ECM) in rPbTIP intravenous injection (i.v.) group was alleviated by the downregulation of pro-inflammatory responses, and rPbTIP i.v. group elicited an expansion of regulatory T-cell response. Therefore, rPbTIP i.v. group displayed less severe brain pathology and feverish mice in rPbTIP i.v. group died from ECM. This study suggested that PbTIP may be a novel promising target to alleviate the severity of ECM.

Screening and identification of potential novel biomarker for diagnosis of complicated Plasmodium vivax malaria

Background

In the recent years Plasmodium vivax has been reported to cause severe infections associated with mortality. Clinical evaluation has limited accuracy for the early identification of the patients progressing towards the fatal condition. Researchers have tried to identify the serum and the plasma-based indicators of the severe malaria. Discovery of MicroRNA (miRNA) has opened up an era of identification of early biomarkers for various infectious and non-infectious diseases. MicroRNAs (miRNA) are the small non-coding RNA molecules of length 19–24 nts and are responsible for the regulation of the majority of human gene expressions at post transcriptional level.

Methods

We identified the differentially expressed miRNAs by microarray and validated the selected miRNAs by qRT-PCR. We assessed the diagnostic potential of these up-regulated miRNAs for complicated P. vivax malaria. Futher, the bioinformtic analysis was performed to construct protein–protein and mRNA–miRNA networks to identify highly regulated miRNA.

Results

In the present study, utility of miRNA as potential biomarker of complicated P. vivax malaria was explored. A total of 276 miRNAs were found to be differentially expressed by miRNA microarray and out of which 5 miRNAs (hsa-miR-7977, hsa-miR-28-3p, hsa-miR-378-5p, hsa-miR-194-5p and hsa-miR-3667-5p) were found to be significantly up-regulated in complicated P. vivax malaria patients using qRT-PCR. The diagnostic potential of these 5 miRNAs were found to be significant with sensitivity and specificity of 60–71% and 69–81% respectively and area under curve (AUC) of 0.7 (p < 0.05). Moreover, in silico analysis of the common targets of up-regulated miRNAs revealed UBA52 and hsa-miR-7977 as majorly regulated hubs in the PPI and mRNA–miRNA networks, suggesting their putative role in complicated P. vivax malaria.

Conclusion

miR-7977 might act as a potential biomarker for differentiating complicated P. vivax malaria from uncomplicated type. The elevated levels of miR-7977 may have a role to play in the disease pathology through UBA52 or TGF-beta signalling pathway.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1646-9) contains supplementary material, which is available to authorized users.

Cytokine modulation of human blood viscosity from vivax malaria patients

Malaria is a major infectious disease in several countries and is caused by protozoa of the genus Plasmodium. In vivax malaria patients, inflammatory processes occur, as well as changes in cytokines and blood flow. The present study analyzed the cytokine modulation of blood viscosity from patients infected with Plasmodium vivax (P. vivax). Blood samples were collected from 42 non-infected individuals (control group) and 37 individuals infected with P. vivax. The IL-2, IL-4, IL-6, IL-10, TNFα, TGF-β and IL-17 cytokine concentrations in the serum were assessed, and the blood rheological properties were determined. The analysis of blood viscosity for shear rates revealed that the blood viscosity of the infected patients was significantly greater than that of the non-infected individuals. The viscosity of the blood was greater in the infected individuals than in the non-infected subjects. The serum from individuals with P. vivax infections exhibited higher IFN-γ and IL-17 concentrations and lower TGF-β levels. Incubation of the blood from infected individuals with IL-17 or IL-17 associated with IFN-γ reduced the viscosity to rates equivalent to the blood from non-infected individuals. Independently of cytokine modulation, no correlation was found between the parasitemia and blood viscosity of the infected patients. These data suggest that the alterations of blood viscosity are relevant as an auxiliary tool for the clinical diagnosis of disease. In malaria, erythrocytes are more sensitive to osmotic shock, and the reduction of viscosity by IL-17 may be related to a possible immunomodulator agent during infection.

Thrombocytopenia May Mediate Disease Severity in Plasmodium falciparum Malaria Through Reduced Transforming Growth Factor Beta-1 Regulation of Proinflammatory and Anti-inflammatory Cytokines

BACKGROUND

Transforming growth factor beta-1 (TGF-β1) is an important regulator of inflammation. Platelets are a major source of TGF-β1 and are reduced in severe malaria. However, the relationships between TGF-β1 concentrations and platelet counts, proinflammatory and anti-inflammatory cytokine and chemokine concentrations and disease severity in malaria have not been characterized.

METHODS

Platelet counts and serum concentrations of TGF-β1, interleukin-1beta (IL-1β), IL-6, IL-10, interferon (IFN)-γ, tumor necrosis factor (TNF)-α and RANTES were measured at the time of presentation in Ugandan children with cerebral malaria (CM, n = 75), uncomplicated malaria (UM, n = 67) and healthy community children (CC, n = 62).

RESULTS

TGF-β1 concentrations decreased with increasing severity of disease [median concentrations (25th, 75th percentile) in ng/mL in CC, 41.4 (31.6, 57.4); UM, 22.7 (14.1, 36.4); CM, 11.8 (8, 21); P for trend < 0.0001]. In children with CM or UM, TGF-β1 concentrations correlated positively with platelet count (CM, P < 0.0001; UM, P = 0.0015). In children with CM, TGF-β1 concentration correlated negatively with IFN-γ, IL-6 and IL-10 and positively with RANTES concentrations (all P < 0.01). TGF-β1 concentration was not associated with death or adverse neurologic or cognitive outcomes in children with CM.

CONCLUSIONS

TGF-β1 concentrations decrease with increasing Plasmodium falciparum disease severity. In CM, thrombocytopenia correlates with decreased TGF-β1, and decreased TGF-β1 correlates with cytokine/chemokine changes associated with increased disease severity and death. Thrombocytopenia may mediate disease severity in malaria through reduced TGF-β1-mediated regulation of cytokines associated with severe disease.

Autoantibody profile of patients infected with knowlesi malaria

BACKGROUND

Autoantibodies or antibodies against self-antigens are produced either during physiological processes to maintain homeostasis or pathological process such as trauma and infection. Infection with parasites including Plasmodium has been shown to generally induce elevated self-antibody (autoantibody) levels. Plasmodium knowlesi is increasingly recognized as one of the most important emerging human malaria in Southeast Asia that can cause severe infection leading to mortality. Autoimmune-like phenomena have been hypothesized to play a role in the protective immune responses in malaria infection.

METHODS

We studied the autoantibody profile from serum of eleven patients diagnosed with P. knowlesi. Autoantigen arrays were used to elucidate the autoantibody repertoire of P. knowlesi infected patients. The patented OGT Discovery Array with 1636 correctly folded antigen was employed.

RESULTS

Analysis of the patient versus control sera gave us 24 antigens with high reactivity with serum antibodies.

CONCLUSIONS

Understanding the autoantibody profile of malarious patients infected with P. knowlesi would help to further understand the host-parasite interaction, host immune response and disease pathogenesis. These reactive antigens may serve as potential biomarkers for cases of asymptomatic malaria and mild malaria or predictive markers for severe malaria.

Plasmodium falciparum-mediated induction of human CD25Foxp3 CD4 T cells is independent of direct TCR stimulation and requires IL-2, IL-10 and TGFbeta

CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) regulate disease-associated immunity and excessive inflammatory responses, and numbers of CD4(+)CD25(+)Foxp3(+) Tregs are increased during malaria infection. The mechanisms governing their generation, however, remain to be elucidated. In this study we investigated the role of commonly accepted factors for Foxp3 induction, TCR stimulation and cytokines such as IL-2, TGFbeta and IL-10, in the generation of human CD4(+)CD25(+)Foxp3(+) T cells by the malaria parasite Plasmodium falciparum. Using a co-culture system of malaria-infected red blood cells (iRBCs) and peripheral blood mononuclear cells from healthy individuals, we found that two populations of Foxp3(hi) and Foxp3(int) CD4(+)CD25(hi) T cells with a typical Treg phenotype (CTLA-4(+), CD127(low), CD39(+), ICOS(+), TNFRII(+)) were induced. Pro-inflammatory cytokine production was confined to the Foxp3(int) subset (IFNgamma, IL-4 and IL-17) and inversely correlated with high relative levels of Foxp3(hi) cells, consistent with Foxp3(hi) CD4 T cell-mediated inhibition of parasite-induced effector cytokine T cell responses. Both Foxp3(hi) and Foxp3(int) cells were derived primarily from proliferating CD4(+)CD25(-) T cells with a further significant contribution from CD25(+)Foxp3(+) natural Treg cells to the generation of the Foxp3(hi) subset. Generation of Foxp3(hi), but not Foxp3(int), cells specifically required TGFbeta1 and IL-10. Add-back experiments showed that monocytes expressing increased levels of co-stimulatory molecules were sufficient for iRBC-mediated induction of Foxp3 in CD4 T cells. Foxp3 induction was driven by IL-2 from CD4 T cells stimulated in an MHC class II-dependent manner. However, transwell separation experiments showed that direct contact of monocytes with the cells that acquire Foxp3 expression was not required. This novel TCR-independent and therefore antigen-non specific mechanism for by-stander CD4(+)CD25(hi)Foxp3(+) cell induction is likely to reflect a process also occurring in vivo as a consequence of immune activation during malaria infection, and potentially a range of other infectious diseases.

Homeostatic regulation of T effector to Treg ratios in an area of seasonal malaria transmission

An important aspect of clinical immunity to malaria is the ability to down-regulate inflammatory responses, once parasitaemia is under control, in order to avoid immune-mediated pathology. The role of classical (CD4(+)CD25(+)CD127(lo/-)FOXP3(+)) Treg in this process, however, remains controversial. Thus, we have characterized the frequency, phenotype and function of Treg populations, over time, in healthy individuals in The Gambia. We observed that both the percentage and the absolute number of CD4(+)FOXP3(+)CD127(lo/-) T cells were higher among individuals living in a rural village with highly seasonal malaria transmission than among individuals living in an urban area where malaria rarely occurs. These CD4(+)FOXP3(+)CD127(lo/-) T cells exhibited an effector memory and apoptosis-prone phenotype and suppressed cytokine production in response to malaria antigen. Cells from individuals exposed to malaria expressed significantly higher levels of mRNA for forkhead box P3 and T-box 21 (T-BET) at the end of the malaria transmission season than at the end of the non-transmission season. Importantly, the ratio of T-BET to forkhead box P3 was remarkably consistent between populations and over time, indicating that in healthy individuals, a transient increase in Th1 responses during the malaria transmission season is balanced by a commensurate Treg response, ensuring that immune homeostasis is maintained.

Distinct roles for FOXP3 and FOXP3 CD4 T cells in regulating cellular immunity to uncomplicated and severe Plasmodium falciparum malaria

Failure to establish an appropriate balance between pro- and anti-inflammatory immune responses is believed to contribute to pathogenesis of severe malaria. To determine whether this balance is maintained by classical regulatory T cells (CD4(+) FOXP3(+) CD127(-/low); Tregs) we compared cellular responses between Gambian children (n = 124) with severe Plasmodium falciparum malaria or uncomplicated malaria infections. Although no significant differences in Treg numbers or function were observed between the groups, Treg activity during acute disease was inversely correlated with malaria-specific memory responses detectable 28 days later. Thus, while Tregs may not regulate acute malarial inflammation, they may limit memory responses to levels that subsequently facilitate parasite clearance without causing immunopathology. Importantly, we identified a population of FOXP3(-), CD45RO(+) CD4(+) T cells which coproduce IL-10 and IFN-gamma. These cells are more prevalent in children with uncomplicated malaria than in those with severe disease, suggesting that they may be the regulators of acute malarial inflammation.

MAPK ERK signaling regulates the TGF-beta1-dependent mosquito response to Plasmodium falciparum

Malaria is caused by infection with intraerythrocytic protozoa of the genus Plasmodium that are transmitted by Anopheles mosquitoes. Although a variety of anti-parasite effector genes have been identified in anopheline mosquitoes, little is known about the signaling pathways that regulate these responses during parasite development. Here we demonstrate that the MEK-ERK signaling pathway in Anopheles is controlled by ingested human TGF-beta1 and finely tunes mosquito innate immunity to parasite infection. Specifically, MEK-ERK signaling was dose-dependently induced in response to TGF-beta1 in immortalized cells in vitro and in the A. stephensi midgut epithelium in vivo. At the highest treatment dose of TGF-beta1, inhibition of ERK phosphorylation increased TGF-beta1-induced expression of the anti-parasite effector gene nitric oxide synthase (NOS), suggesting that increasing levels of ERK activation negatively feed back on induced NOS expression. At infection levels similar to those found in nature, inhibition of ERK activation reduced P. falciparum oocyst loads and infection prevalence in A. stephensi and enhanced TGF-beta1-mediated control of P. falciparum development. Taken together, our data demonstrate that malaria parasite development in the mosquito is regulated by a conserved MAPK signaling pathway that mediates the effects of an ingested cytokine.

Low levels of mammalian TGF-beta1 are protective against malaria parasite infection, a paradox clarified in the mosquito host

Nitric oxide (NO), derived from catalysis of inducible NO synthase (iNOS), limits malaria parasite growth in mammals. Transforming growth factor (TGF)-beta1 suppresses iNOS in cells in vitro as well as in vivo in mice, but paradoxically severe malaria in humans is associated with low levels of TGF-beta1. We hypothesized that this paradox is a universal feature of infection and occurs in the mosquito Anopheles stephensi, an invertebrate host for Plasmodium that also regulates parasite development with inducible NO synthase (AsNOS). We show that exogenous human TGF-beta1 dose-dependently regulates mosquito AsNOS expression and that parasite killing by low dose TGF-beta1 depends on AsNOS catalysis. Furthermore, induction of AsNOS expression by TGF-beta1 is regulated by NO synthesis. These results suggest that TGF-beta1 plays similar roles during parasite infection in mammals and mosquitoes and that this role is linked to the effects of TGF-beta1 on inducible NO synthesis.

Innate Immune Responses to Human Malaria: Heterogeneous Cytokine Responses to Blood-Stage Plasmodium falciparum Correlate with Parasitological and Clinical Outcomes

Taking advantage of a sporozoite challenge model established to evaluate the efficacy of new malaria vaccine candidates, we have explored the kinetics of systemic cytokine responses during the prepatent period of Plasmodium falciparum infection in 18 unvaccinated, previously malaria-naive subjects, using a highly sensitive, bead-based multiplex assay, and relate these data to peripheral parasite densities as measured by quantitative real-time PCR. These data are complemented with the analysis of cytokine production measured in vitro from whole blood or PBMC, stimulated with P. falciparum-infected RBC. We found considerable qualitative and quantitative interindividual variability in the innate responses, with subjects falling into three groups according to the strength of their inflammatory response. One group secreted moderate levels of IFN-gamma and IL-10, but no detectable IL-12p70. A second group produced detectable levels of circulating IL-12p70 and developed very high levels of IFN-gamma and IL-10. The third group failed to up-regulate any significant proinflammatory responses, but showed the highest levels of TGF-beta. Proinflammatory responses were associated with more rapid control of parasite growth but only at the cost of developing clinical symptoms, suggesting that the initial innate response may have far-reaching consequences on disease outcome. Furthermore, the in vitro observations on cytokine kinetics presented here, suggest that intact schizont-stage infected RBC can trigger innate responses before rupture of the infected RBC.

Upregulation of TGF-β, FOXP3, and CD4+CD25+ Regulatory T Cells Correlates with More Rapid Parasite Growth in Human Malaria Infection

Understanding the regulation of immune responses is central for control of autoimmune and infectious disease. In murine models of autoimmunity and chronic inflammatory disease, potent regulatory T lymphocytes have recently been characterized. Despite an explosion of interest in these cells, their relevance to human disease has been uncertain. In a longitudinal study of malaria sporozoite infection via the natural route, we provide evidence that regulatory T cells have modifying effects on blood-stage infection in vivo in humans. Cells with the characteristics of regulatory T cells are rapidly induced following blood-stage infection and are associated with a burst of TGF-beta production, decreased proinflammatory cytokine production, and decreased antigen-specific immune responses. Both the production of TGF-beta and the presence of CD4+CD25+FOXP3+ regulatory T cells are associated with higher rates of parasite growth in vivo. P. falciparum-mediated induction of regulatory T cells may represent a parasite-specific virulence factor.

Reduced levels of transforming growth factor-beta1, interleukin-12 and increased migration inhibitory factor are associated with severe malaria

In the present study, we investigated plasma levels of interleukin (IL)-12 and transforming growth factor (TGF-beta1) in malaria patients as these two cytokines regulate the balance between pro- and anti-inflammatory cytokines. We compared plasma IL-12 and TGF-beta1 levels in groups of malaria patients categorized as uncomplicated, severe, cerebral and placental malaria. Both TGF-beta1 and IL-12 levels were significantly reduced in peripheral plasma of adults with severe and cerebral malaria as well as in plasma of Tanzanian children with cerebral malaria (P<0.05). Similar results were observed with both placental and peripheral plasma of pregnant women who were infected with Plasmodium falciparum. IL-18, a cytokine known to be critical for the induction of IFN-gamma along with IL-1, was produced more in uncomplicated adult patients than in aparasitimic healthy controls (P<0.05). However, IL-18 response rate declined as the symptoms of the disease became more severe suggesting that the IL-18 response may be impaired with increased malaria severity. Together, the results of the three cytokines support the notion that imbalance between pro- and anti-inflammatory cytokines may contribute to the development of severe malaria infection. With malaria infection during pregnancy, we demonstrated that macrophage migration inhibitory factor (MIF) levels in infected placental plasma were significantly higher than those in the paired peripheral plasma (P<0.05). MIF, therefore, may play an important role in the local immune response to placental P. falciparum infection.

Activation of transforming growth factor beta by malaria parasite-derived metalloproteinases and a thrombospondin-like molecule

Much of the pathology of malaria is mediated by inflammatory cytokines (such as interleukin 12, interferon γ, and tumor necrosis factor α), which are part of the immune response that kills the parasite. The antiinflammatory cytokine transforming growth factor (TGF)-β plays a crucial role in preventing the severe pathology of malaria in mice and TGF-β production is associated with reduced risk of clinical malaria in humans. Here we show that serum-free preparations of Plasmodium falciparum, Plasmodium yoelii 17XL, and Plasmodium berghei schizont-infected erythrocytes, but not equivalent preparations of uninfected erythrocytes, are directly able to activate latent TGF-β (LatTGF-β) in vitro. Antibodies to thrombospondin (TSP) and to a P. falciparum TSP-related adhesive protein (PfTRAP), and synthetic peptides from PfTRAP and P. berghei TRAP that represent homologues of TGF-β binding motifs of TSP, all inhibit malaria-mediated TGF-β activation. Importantly, TRAP-deficient P. berghei parasites are less able to activate LatTGF-β than wild-type parasites and their replication is attenuated in vitro. We show that activation of TGF-β by malaria parasites is a two step process involving TSP-like molecules and metalloproteinase activity. Activation of LatTGF-β represents a novel mechanism for direct modulation of the host response by malaria parasites.

Pathology of Plasmodium chabaudi chabaudi infection and mortality in interleukin-10-deficient mice are ameliorated by anti-tumor necrosis factor alpha and exacerbated by anti-transforming growth factor beta antibodies

Interleukin-10 (IL-10)-deficient (IL-10(-/-)) mice infected with Plasmodium chabaudi (AS) suffer a more severe disease and exhibit a higher rate of mortality than control C57BL/6 mice. Here, we show that a drop in body temperature to below 28 degrees C and pronounced hypoglycemia of below 3 mM are reliable indicators of a lethal infection. Elevated inflammatory responses have been shown to accompany pathology in infected IL-10(-/-) mice. We show that neutralization of tumor necrosis factor alpha (TNF-alpha) in IL-10(-/-) mice abolishes mortality and ameliorates the hypothermia, weight loss, and anemia but does not affect the degree of hypoglycemia. These data suggest that TNF-alpha is involved in some of the pathology associated with a P. chabaudi infection in IL-10(-/-) mice but other factors play a role. IL-10(-/-) mice that survive a primary infection have been shown to control gamma interferon (IFN-gamma) and TNF-alpha production, indicating that other cytokines or mechanisms may be involved in their down-regulation. Significantly higher levels of transforming growth factor beta (TGF-beta), a cytokine with such properties, are present in the plasma of infected IL-10(-/-) mice at a time that coincides with the disappearance of IFN-gamma and TNF-alpha from the blood. Neutralization of TGF-beta in IL-10(-/-) mice resulted in higher circulating amounts of TNF-alpha and IFN-gamma, and all treated IL-10(-/-) mice died within 12 days with increased pathology but with no obvious increase in parasitemia. Our data suggest that a tight regulation of the balance between regulatory cytokines such as IL-10 and TGF-beta and inflammatory cytokines such as IFN-gamma and TNF-alpha is critical for survival in a mouse malaria infection.

The immune response to Plasmodium falciparum malaria

Malaria is still a major cause of severe disease which is responsible for millions of deaths, mostly in children under 5 years old, in tropical countries, especially sub-Saharan Africa. Complications of severe anaemia and cerebral malaria are thought to be the major cause of morbidity and mortality but recent evidence suggests that the host's immunological response could also contribute to the pathophysiology of the disease in human beings. Intensive studies of the immune response to malaria parasites in human beings have provided a wealth of information about the cells and cytokines implicated in the pathophysiology of survival and fatal outcome in severe infections. This review focuses on the pivotal role of macrophages and other important cellular effectors, molecules, and cytokines involved in the activation of the immune response at the different stages of human falciparum malaria. Our understanding of the putative mechanisms by which cytokines may mediate beneficial and harmful effects, through activation of phagocytic cells, could help to develop new treatment strategies, regardless of the emergence of parasite multidrug resistance.

Changes in cytokine production associated with acquired immunity to Plasmodium falciparum malaria

Individuals living in malaria-endemic areas eventually develop clinical immunity to Plasmodium falciparum. That is, they are able to limit blood parasite densities to extremely low levels and fail to show symptoms of infection. As the clinical symptoms of malaria infection are mediated in part by pro-inflammatory cytokines it is not clear whether the acquisition of clinical immunity is due simply to the development of antiparasitic mechanisms or whether the ability to regulate inflammatory cytokine production is also involved. We hypothesize that there is a correlation between risk of developing clinical malaria and the tendency to produce high levels of proinflammatory cytokines in response to malaria infection. In order to test this hypothesis, we have compared the ability of peripheral blood mononuclear cells from malaria-naive and malaria-exposed adult donors to proliferate and to secrete IFN-gamma in response to P. falciparum schizont extract (PfSE). In order to determine how PfSE-induced IFN-gamma production is regulated, we have also measured production of IL-12p40 and IL-10 from PfSE-stimulated PBMC and investigated the role of neutralizing antibody to IL-12 in modulating IFN-gamma production. We find that cells from naive donors produce moderate amounts of IFN-gamma in response to PfSE and that IFN-gamma production is strongly IL-12 dependent. Cells from malaria-exposed donors living in an area of low malaria endemicity produce much higher levels of IFN-gamma and this response is also at least partially IL-12 dependent. In complete contrast, cells from donors living in an area of very high endemicity produce minimal amounts of IFN-gamma. No significant differences were detected between the groups in IL-10 production, suggesting that this cytokine does not play a major role in regulating malaria-induced IFN-gamma production. The data from this study thus strongly support the hypothesis that down-regulation of inflammatory cytokine production may be a component of acquired clinical immunity to malaria but the mechanism by which this is achieved remains to be elucidated.

Transforming growth factor beta concentrations and interferon gamma responses in cerebrospinal fluid of horses with equine protozoal myeloencephalitis

The following experiment was performed to test the hypothesis that transforming growth factor beta (TGF-beta) concentration varies in the cerebrospinal fluid and serum of horses with EPM and to determine if cerebrospinal fluid (CSF) alters the interferon-gamma (IFN-gamma) rersponse of equine peripheral blood mononuclear cells (PBMCs). The concentration of transforming growth factor-beta (TGF-beta2) was investigated in the serum and cerebrospinal fluid (CSF) of 18 horses (9 normal, 9 affected with equine protozoal myeloencephalitis [EPM]). The TGF-beta2 assay was validated in a group of 6 normal horses. Intra-assay variability was 4.7%, and interassay variability was 10.7%. The slope of the curve of the unknown samples of various volumes demonstrated parallelism with a curve developed using equal volumes of assay kit standard. Assay of normal and EPM-affected horses found that TGF-beta2 was present in both the serum and CSF of all animals. However, the concentration of TGF-beta2 in the CSF was less (P = 0.03) in EPM-affected horses (144 pg/ml) than in normal horses (256 pg/ml). In addition, the effect of CSF from normal and EPM-affected horses on the production of interferon-gamma (IFN-gamma) by PHA-P stimulated PBMCs from normal horses was investigated using a bioassay. It was found that CSF from normal and EPM-affected horses enhanced IFN-gamma activity from PHA-P stimulated peripheral blood mononuclear cells (P < or = 0.05); however, the response to CSF from EPM-affected horses was no different than the response to CSF from normal horses. Treatment of cells with anti-TGF-beta2 monoclonal antibodies slightly increased the response when co-incubated with CSF from normal horses, and slightly decreased it when co-incubated with CSF from EPM-affected horses. These differences, however, did not achieve statistical significance (P > 0.05). Results of this study indicated that production of TGF-beta2 is altered in horses with EPM, and that CSF appears to contain substances which alter the inflammatory reaction to plant lectins. These findings confirm the immunomodulatory properties of CSF and suggest new techniques for future research regarding the pathophysiology of EPM.

Serial measurement of vascular endothelial growth factor and transforming growth factor-beta1 in serum of patients with acute ischemic stroke

BACKGROUND AND PURPOSE

Both vascular endothelial growth factor (VEGF) and transforming growth factor-beta1 (TGF-beta1) are expressed in higher than normal concentrations in the penumbra of patients after ischemic stroke. Because both cytokines are central to the processes of angiogenesis, tissue inflammation, and fibrosis, we performed serial measurements of these cytokines in patients with cerebral infarction and determined their relationship to stroke etiology and volume.

METHODS

We serially (at days 0, 1, 3, 7, and 14) measured the serum levels of VEGF and active TGF-beta1 in 29 patients with acute ischemic stroke. Age-matched healthy subjects (n=26) were used as controls.

RESULTS

Expression of VEGF was significantly increased in the majority of patients after acute stroke at each of the time points compared with normal controls. Highest expression occurred at day 7 (588+/-121 pg/mL; P=0.005), and it remained significantly elevated at 14 days after stroke. Expression of VEGF correlated with infarct volume, clinical disability (Scandinavian Stroke Scale), and peripheral leukocytosis and was significantly higher in patients with atherothrombotic large-vessel disease and ischemic heart disease (P<0.05 in all cases). In contrast, expression of active TGF-beta1 was not significantly different from control patients at any of the measured time points. When the mean concentration of TGF-beta1 from each patient (pooled time points) was compared with the control mean, a significant increase was found in only 2 patients, whereas levels decreased in 12 patients (P<0.05). There was no correlation between circulating active TGF-beta1 and VEGF expression, leukocytosis, stroke subtype, or patient disability as assessed by Scandinavian Stroke Scale score.

CONCLUSIONS

VEGF but not TGF-beta1 showed a dramatic increase in serum of stroke patients. Correlation between stroke severity and VEGF concentration suggests it could be involved in the subsequent repair processes resulting in partial recovery after stroke. Correlation between VEGF expression and peripheral leukocytosis suggests that these changes may also reflect the immunologic status of the patient. VEGF may play an important role in the pathophysiology of acute ischemic stroke and could be of value in future treatment strategies.

Blood-brain barrier function in cerebral malaria and CNS infections in Vietnam

BACKGROUND

The intraerythrocytic parasite Plasmodium falciparum induces the life-threatening neurologic syndrome of cerebral malaria (CM) from within cerebral blood vessels, without entering the brain parenchyma.

OBJECTIVES

1) To assess the use of CSF as an indicator of specific pathologic processes occurring in the brain during CM; 2) to compare this with other neurologic and infectious diseases to understand the distinct pathogenic features of CM; 3) to test the hypothesis that CM involves a specific functional breakdown of the blood-brain barrier (BBB).

METHODS

1) Radial immunodiffusion assays to detect albumin and IgG in matched plasma and CSF samples as indicators of BBB integrity and intrathecal IgG production; and 2) ELISA for soluble intracellular adhesion molecule-1 and sE-selectin, the cytokines tumor necrosis factor-alpha and transforming growth factor-beta1, and the matrix metalloproteinase MMP-9, to detect cellular activation and inflammatory responses within the brain.

RESULTS

Albumin and IgG indices implied only minimal degree of BBB breakdown in a few cases of CM, with most remaining within the normal range. In contrast, cryptococcal, tubercular, and acute bacterial meningitis produced detectable changes in the composition of the CSF and evidence of BBB breakdown.

CONCLUSIONS

CM appears to involve only subtle functional changes in BBB integrity with minimal intraparenchymal inflammatory responses compared with other neurologic infections. This focuses attention on local events within and around the cerebral microvasculature in CM, rather than indicating widespread parenchymal disease.

Maintaining the immunological balance in parasitic infections: a role for TGF-beta?

Transforming growth factor beta (TGF-beta) is an important regulator of inflammation, being proinflammatory at low concentrations and anti-inflammatory at high concentrations. As such, TGF-beta might be important in maintaining the balance between control and clearance of infectious organisms on the one hand and prevention of immune-mediated pathology on the other. In this article, Fakhereldin Omer, Jørgen Kurtzhals and Eleanor Riley review the immunoregulatory properties of TGF-beta in the context of parasitic infections. Data from murine malaria infections suggest that TGF-beta modifies the severity of the disease, and a number of potential protective mechanisms are discussed. Evidence is accumulating that TGF-beta is important for the regulation of other host-parasite interactions and that parasites might directly influence TGF-beta-dependent pathways via the synthesis of TGF-beta or TGF-beta-receptor homologues.

A role for cytokines in potentiation of malaria vaccines through immunological modulation of blood stage infection

Malaria is the world's major parasitic disease, for which effective control measures are urgently needed. One of the difficulties hindering successful vaccine design against Plasmodium is an incomplete knowledge of antigens eliciting protective immunity, the precise types of immune response for which to aim, and how these can be induced. A greater appreciation of the mechanisms of protective immunity, on the one hand, and of immunopathology, on the other, should provide critical clues to how manipulation of the immune system may best be achieved. We are studying the regulation of the balance between T helper 1 (Th1) and T helper 2 (Th2) CD4+ T lymphocytes in immunity to asexual blood stages of malaria responsible for the pathogenicity of the disease. Protective immunity to the experimental murine malarias Plasmodium chabaudi and Plasmodium yoelii involves both Th1 and Th2 cells, which provide protection by different mechanisms at different times of infection characterised by higher and lower parasite densities, respectively. This model therefore facilitates a clearer understanding of the Th1/Th2 equilibrium that appears central to immunoregulation of all host/pathogen relationships. It also permits a detailed dissection in vivo of the mechanisms of antimalarial immunity. Here, we discuss the present state of malaria vaccine development and our current research to understand the factors involved in the modulation of vaccine-potentiated immunity.

Transforming growth factor beta-induced failure of resistance to infection with blood-stage Plasmodium chabaudi in mice

The role of transforming growth factor beta (TGF-beta) in infection with Plasmodium chabaudi was investigated with resistant and susceptible mouse models. C57BL/10 mice produced gamma interferon (IFN-gamma) and nitric oxide (NO) shortly after infection and cleared the parasite spontaneously. In contrast, BALB/c mice showed a transient enhancement of TGF-beta production, followed by a relative lack of IFN-gamma and NO production, and succumbed to the infection. However, there was no correlation between levels of serum TGF-beta and splenic TGF-beta mRNA in both mouse strains before and after infection. Administration of recombinant TGF-beta (rTGF-beta) rendered resistant mice susceptible because of suppression of subsequent production of IFN-gamma and NO. Administration of anti-TGF-beta antibody to the infected BALB/c mice resulted in remarkable increases in serum IFN-gamma and NO, and the mice resisted the infection. Splenic CD4(+) T and CD11b+ cells of C57BL/10 mice were significantly activated after infection, but this was completely abrogated by administration of rTGF-beta. These results suggested that, in the P. chabaudi-susceptible but not resistant mice, production of TGF-beta was promoted, and subsequent failure of IFN-gamma- and NO-dependent resistance to the parasite was induced. This study is the first to indicate that TGF-beta production was the key event in failure of resistance to mouse malaria.

Time course of immunological markers in patients with the systemic inflammatory response syndrome: evaluation of sCD14, sVCAM-1, sELAM-1, MIP-1 alpha and TGF-beta 2

BACKGROUND

The systemic inflammatory response syndrome (SIRS) is viewed as a system-wide inflammatory response. Up until now, no parameter has been available for predicting the development of septic shock. In the present study, we evaluated the usefulness of serum levels of CD14, vascular cells adhesion molecule-1 (VCAM-1), endothelial leucocyte adhesion molecule-1 (ELAM-1), macrophage inflammatory protein (MIP) 1 alpha and transforming growth factor beta 2 (TGF-beta 2) as early markers of outcome in patients with SIRS.

METHODS

A group of 28 SIRS patients (13 survivors/15 non-survivors) was compared with a healthy control group and with patients with local inflammation. Blood samples were analysed on days 0, 4 and 7. Proinflammatory parameters such as sCD14, sVCAM-1, sELAM-1, MIP-1 alpha and anti-inflammatory parameters such as TGF-beta 2 were determined using enzyme-linked immunosorbent assay (ELISA).

RESULTS

At the beginning, all evaluated proinflammatory immunological parameters with the exception of sVCAM-1 were significantly increased in patients with SIRS compared with the healthy control group. However, no significant difference could be observed for all immunological parameters comparing survivors and non-survivors, with the exception of interleukin (IL) 6 at day 7.

CONCLUSION

All evaluated proinflammatory parameters were increased in patients with SIRS during the course of the disease. However, the parameters have no correlation with outcome and prognosis of SIRS patients.

Transforming growth factor beta production is inversely correlated with severity of murine malaria infection

We have examined the role of the immunomodulatory cytokine transforming growth factor (TGF)-beta in the resolution and pathology of malaria in BALB/c mice. Circulating levels of TGF-beta, and production of bioactive TGF-beta by splenocytes, were found to be low in lethal infections with Plasmodium berghei. In contrast, resolving infections with P. chabaudi chabaudi or P. yoelii were accompanied by significant TGF-beta production. A causal association between the failure to produce TGF-beta and the severity of malaria infection was demonstrated by treatment of infected mice with neutralizing antibody to TGF-beta, which exacerbated the virulence of P. berghei and transformed a resolving P. chabaudi chabaudi infection into a lethal infection, but had little effect on the course of P. yoelii infection. Parasitemia increased more rapidly in anti-TGF-beta-treated mice but this did not seem to be the explanation for the increased pathology of infection as peak parasitemias were unchanged. Treatment of P. berghei-infected mice with recombinant TGF-beta (rTGF-beta) slowed the rate of parasite proliferation and prolonged their survival from 15 to up to 35 d. rTGF-beta treatment was accompanied by a significant decrease in serum tumor necrosis factor alpha and an increase in interleukin 10. Finally, we present evidence that differences in TGF-beta responses in different malaria infections are due to intrinsic differences between species of malaria parasites in their ability to induce production of TGF-beta. Thus, TGF-beta seems to induce protective immune responses, leading to slower parasite growth, early in infection, and, subsequently, appears to downregulate pathogenic responses late in infection. This duality of effect makes TGF-beta a prime candidate for a major immunomodulatory cytokine associated with successful control of malaria infection.

Low plasma concentrations of interleukin 10 in severe malarial anaemia compared with cerebral and uncomplicated malaria

BACKGROUND

Severe anaemia is a major complication of malaria but little is known about its pathogenesis. Experimental models have implicated tumour necrosis factor (TNF) in induction of bone-marrow suppression and eythrophagocytosis. Conversely, interleukin 10 (IL-10), which mediates feed-back regulation of TNF, stimulates bone-marrow function in vitro and counteracts anaemia in mice. We investigated the associations of these cytokines with malarial anaemia.

METHODS

We enrolled 175 African children with malaria into two studies in 1995 and 1996. In the first study, children were classified as having severe anaemia (n=10), uncomplicated malaria (n=26), or cerebral anaemia (n=41). In the second study, patients were classified as having cerebral malaria (n=33) or being fully conscious (n=65), and the two groups were subdivided by measured haemoglobin as normal (>110 g/L), moderate anaemia (60-90 g/L), and severe anaemia (<50 g/L). IL-10 and TNF concentrations were measured by ELISA in plasma samples from all patients.

FINDINGS

IL-10 concentrations were significantly lower in patients with severe anaemia than in all other groups. In 1995, geometric mean plasma IL-10 in patients with severe anaemia was 270 pg/mL (95% CI 152-482) compared with 725 pg/mL (465-1129) in uncomplicated malaria and 966 pg/mL (612-1526) in cerebral malaria (p<0.03). In 1996, fully conscious patients with severe anaemia also had significantly lower IL-10 concentrations than all other groups, including cerebral-malaria patients with severe anaemia and all patients with moderate anaemia (p<0.001). In both studies, TNF concentrations were significantly higher in cerebral malaria than in fully conscious patients (p<0.01). By contrast, the ratio of TNF to IL-10 was significantly higher in fully conscious patients with severe anaemia than in all other groups (p<0.001).

INTERPRETATION

Our findings identify severe malarial anaemia as a distinct disorder in which insufficient IL-10 response to high TNF concentrations may have a central role.

Prognostic value of MIP-1 alpha, TGF-beta 2, sELAM-1, and sVCAM-1 in patients with gram-positive sepsis

The aim of the present study was to evaluate the potential prognostic value of MIP-1 alpha, TGF-beta 2, sELAM-1, and sVCAM-1 in patients with gram-positive sepsis. Twenty-eight patients with gram-positive sepsis were compared to 11 patients with gram-negative sepsis and 15 healthy volunteers. Sepsis was defined by the criteria of Bone et al. (Crit. Care Med. 21, 5447-5463, 1993) and by isolation of at least two positive blood cultures with gram-positive/gram-negative bacteria. Plasma samples for determination of the immunological parameters were collected daily. Analysis of cytokines and adhesion molecules was performed on days 0 (day of sepsis criteria fulfillment), 4, and 7 (or 1 day before death). In the gram-positive group 10 of 28 patients died; in the gram-negative group 4 of 11 died. Only sELAM-1 plasma concentrations were found to be a useful early parameter in predicting patients' outcome in gram-positive sepsis. sELAM-1 concentrations at the onset of the study (day 0) were significantly higher in the nonsurviving patients than those in the survivors. MIP-1 alpha levels were significantly higher only on days 4 and 7. With regard to the measured plasma concentrations we believe that MIP-1 alpha is not a useful parameter for predicting patients' prognosis. The increase of sVCAM-1 might play a role in the pathogenesis of gram-positive sepsis; however, it could not be relied upon as an early prognostic parameter. The potential role of TGF-beta 2 in the development of gram-positive sepsis could not evaluated in the present study, whereas routine measurements of TGF-beta 2 offered no additional prognostic information.

Complement activation in severe Plasmodium falciparum malaria

We determined indices of plasma complement activation (C3, C4, Bb, C4d, iC3b, and SC5b-9), levels of tumor necrosis factor (TNF) and interleukin-6, and the APACHE II score in 23 patients with complicated Plasmodium falciparum malaria. On admission, plasma concentrations of Bb, SC5b-9, and C4d were markedly increased compared to healthy control subjects (n = 24) (4.5 +/- 1.9 vs 1.5 +/- 0.6 mg/L; 1125.7 +/- 496.9 vs 183.2 +/- 76.5 microg/L; and 15.7 +/- 5.7 vs 7.2 +/- 1.4 mg/L, P < 0.01 for all). In contrast C3 and iC3b concentrations were decreased (631.4 +/- 247 vs 947.3 +/- 243.2 and 105 +/- 17.9 vs 151.3 +/- 14.5 mg/L; P < 0.01 for both). Plasma C4 concentrations in malaria were not different from normal controls. Plasma Bb, C3, and iC3b levels normalized on day 7 of treatment, whereas SC5b-9 and C4d levels remained elevated. A significant correlation between elevated TNF levels and Bb (r = 0.507) and SC5b-9 (r = 0.448, P < 0.01 for both) and a negative correlation between iC3b and SC5b-9 and TNF levels existed (r = -0.537 and r = -0.466, P < 0.01 for both). In addition, a significant correlation between C3 and iC3b (r = 0.689) and C4 and C4d (r = 0.737) existed. However, no relation between clinical disease severity and complement fragments existed. The results demonstrate that both the classical and the alternative pathways of the complement system are profoundly activated in complicated malaria.

Changes in TGF-beta 1 levels in gingiva, crevicular fluid and serum associated with periodontal inflammation in humans and dogs

Transforming growth factor-beta (TGF-beta) represents a family of polypeptide growth factors, involved in embryogenesis, inflammation, regulation of immune responses and wound healing. To determine whether TGF-beta contributes to the evolution of periodontal disease, we assayed TGF-beta levels in gingiva and crevicular fluid of patients with gingivitis and periodontitis. In parallel, TGF-beta was quantified in gingival fluid and serum of beagles with experimentally-induced periodontitis. Disease was monitored by several clinical parameters including Plaque Index, Gingival Index, probing depth, and epithelial attachment loss. Gingival tissues were obtained from 9 patients at the time of periodontal surgery, and gingival fluid samples were collected from an additional population of 10 periodontal patients. In 14 beagles, experimental periodontitis was induced and gingival fluids collected 6 months later. Fluid was collected by paper strips and volume measured by Periotron. Additionally, sera was collected before and 9 months after the ligature-induced periodontitis in 7 beagles. The levels of TGF-beta 1 were measured by ELISA. In the patients, a significantly higher concentration of TGF-beta 1 was observed both in the gingival tissues and fluid samples obtained from the sites with deeper periodontal pockets than in the less involved sites. In beagles, TGF-beta 1 levels measured in gingival fluid were elevated in moderate disease, declining in fluid samples obtained from the pockets during more advanced experimental periodontitis. Furthermore, with the progression of experimental periodontitis, a decrease in TGF-beta 1 occurred in the sera of the beagle dogs. These data suggest that TGF-beta 1 may play a rôle in the pathogenesis and diagnosis of periodontal disease, and that its actions can be further explored in an animal model.

Monocyte response to bacterial toxins, expression of cell surface receptors, and release of anti-inflammatory cytokines during sepsis

Exposure to endotoxin produces a state of macrophage hyporesponsiveness on subsequent stimulation. Monocytes in patients with septic shock demonstrate a similar hyporesponsiveness to endotoxin. The purpose of this study was to examine whether this state of hyporesponsiveness extends to other inflammatory stimuli and the relationship of this state to cell surface receptor expression and the release of anti-inflammatory cytokines. Twelve normal volunteers, 10 patients with severe sepsis, and 9 patients with septic shock were included in the study. Monocytes from each subject were isolated and stimulated with lipopolysaccharide (LPS), staphylococcal enterotoxin B (SEB), and phorbol myristate acetate (PMA). Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) were measured in the supernatants by enzyme-linked immunosorbent assay (ELISA). Serum levels of transforming growth factor-beta1 (TGF-beta1), prostaglandin E2 (PGE2), and interleukin-10 (IL-10) were also measured by ELISA. The expression of monocyte CD14 and HLA-DR in whole blood were measured by flow cytometry. Patients with septic shock demonstrated significantly decreased TNF-alpha and IL-1beta release as compared with normal subjects in response to LPS. In response to SEB, patients with sepsis and patient with septic shock demonstrated significantly decreased release of TNF-alpha and IL-1beta. Significant decreases in TNF-alpha release were found in the patients with septic shock after PMA stimulation. There were no significant differences in the monocyte response to the different stimuli between patients with gram-positive sepsis and gram-negative sepsis. HLA-DR expression was significantly decreased in patients with septic shock (58 +/- 9 fluorescence units (flU)) as compared with normal subjects (102 +/- 14 flU) (p < 0.05). No differences in CD14 expression were observed. IL-10 levels were significantly increased in patients with sepsis (16 +/- 4 pg/ml) and in patients with septic shock (42 +/- 15 pg/ml) and were detectable in 1 normal subject. TGF-beta1 levels were decreased in patients with septic shock (25 +/- 6 pg/ml) as compared with those in normal subjects (37 +/- 2 pg/ml)(p < 0.05). PGE2 levels were significantly increased in patients with septic shock and patients with sepsis. These data are consistent with a more generalized monocyte hyporesponsiveness to bacterial toxins that may be related to altered cell surface receptor expression and the release of anti-inflammatory cytokines.

Serial measurement of interleukin-6, transforming growth factor-beta, and S-100 protein in patients with acute stroke

BACKGROUND AND PURPOSE

Cytokine changes in patients with acute stroke have been insufficiently studied. The purpose of this study was to delineate the characteristics of serial changes of serum interleukin-6 (IL-6) and transforming growth factor-beta (TGF-beta) in patients with cerebral infarction and intracerebral hemorrhage.

METHODS

We serially (within 24 hours, at day 3, and at day 7) measured the serum levels of IL-6 and TGF-beta in 29 patients with acute stroke (10 with large cortical cerebral infarction, 9 with subcortical small infarction, and 10 with intracerebral hemorrhage). As an index of brain damage. S-100 protein was also measured. Twelve age-matched healthy subjects were tested as a control.

RESULTS

S-100 protein was detected in only 11 patients with large infarction or intracerebral hemorrhage. Its level peaked at day 3 in patients with infarction, whereas it peaked within 24 hours in those with intracerebral hemorrhage. The level of IL-6 was most markedly elevated at day 1, which tended to decrease thereafter. However, its level remained significantly elevated compared with that of the control group even at day 7. The level of TGF-beta was significantly decreased at day 1 and day 3 and tended to return toward the control value thereafter. The levels of both cytokines were not significantly different among the three different stroke subtypes and were not correlated with the number of blood leukocytes and platelets.

CONCLUSIONS

The alteration of IL-6 and TGF-beta levels, which occurs rapidly after acute stroke regardless of the subtype, may reflect the changing immunological-inflammatory status of these patients and does not appear to reflect merely the consequence of the brain damage.

Cytokines and adhesion molecules in stroke and related diseases

Once thought as immunologically naive, cells from the central nervous system have been shown to become immunologically reactive and produce various substances including cytokines and adhesion molecules. Recent investigations have revealed that mRNAs of certain cytokines such as tumor necrosis factor, interleukin-1, and interleukin-6 are expressed in the ischemic brain of the animals. Chemokines including CINC, MCP-1, and MIP-1, as well as adhesion molecules such as ICAM-1. ELAM and P-selectin were also found to be expressed. Although identification of the cells producing these cytokines were often difficult, neurons, endothelia, activated astrocytes and microglia/macrophages were the likely sources. The induction of these molecules in ischemic brain is time-locked and appears to be controlled in a highly regulated manner during the process of ischemic cascade. The functional role, interrelationship, and basic mechanism of action of these molecules are being increasingly recognized, while trials such as antiadhesion antibody molecules, growth factors, and anticytokine antibodies have been successful in reducing the neuronal damage in animals subjected to ischemic injury. Furthermore, changes of certain cytokines or adhesion molecules have been detected in the serum or cerebrospinal fluid of patients with stroke and related diseases suggesting that these molecules play a role in the pathogenesis of human stroke. Understanding of these cytokine-adhesion molecule cascades in the ischemic brain may allow us to develop new strategies for the treatment of stroke.