Depressed Natural Killer Cell Cytotoxicity againstPlasmodium falciparum–Infected Erythrocytes during First Pregnancies

Status of Blood Levels of Superoxide Dismutase in Patients with Malaria: A Systematic Review and Meta-Analysis

Aims: The evidence of superoxide dismutase (SOD) in the pathogenesis of malaria is inconsistent. This study aimed to synthesize the evidence of blood levels of SOD in patients with malaria and determine the association of blood levels of SOD with the severity of malaria. Results: A total of 1874 articles were retrieved from database searches and 28 studies were included in the review. The blood levels of SOD were lower in individuals with malaria compared with those without malaria infection (p < 0.01, Cohen's d: -2.06, 95% CI: -2.99 to -1.14), I2: 98.96%, 2181 malaria cases/1186 uninfected cases). There were no differences in blood levels of SOD between severe and nonsevere malaria patients (p = 0.09, Cohen's d: -1.57, 95% CI: -3.39 to 0.26), I2: 96.02%, 69 severe malaria cases/256 nonsevere malaria cases). Innovation and Conclusion: The blood levels of SOD were lower in malaria patients compared with those without malaria infection. Further studies will be required to determine the extent to which SOD might prevent Plasmodium infections during pregnancy. Antioxid. Redox Signal. 40, 222-235.

Influence of Galectin-9 Treatment on the Phenotype and Function of NK-92MI Cells in the Presence of Different Serum Supplements

Galectins are one of the critical players in the tumor microenvironment-tumor crosstalk and the regulation of local immunity. Galectin-9 has been in the limelight in tumor immunology. Galectin-9 possesses its multiplex biological functions both extracellularly and intracellularly, plays a pivotal role in the modulation of adaptive and innate immunity, and induces immune tolerance. NK-92MI cell lines against different malignancies were extensively studied, and recently published trials used genetically chimeric antigen receptor-transfected NK-92MI cells in tumor immunotherapy. Besides the intensive research in tumor immunotherapy, limited information is available on their immune-checkpoint expression and the impact of checkpoint ligands on their effector functions. To uncover the therapeutic potential of modulating Galectin-9-related immunological pathways in NK-cell-based therapy, we investigated the dose-dependent effect of soluble Galectin-9 on the TIM-3 checkpoint receptor and NKG2D, CD69, FasL, and perforin expression of NK-92MI cells. We also examined how their cytotoxicity and cytokine production was altered after Gal-9 treatment and in the presence of different serum supplements using flow cytometric analysis. Our study provides evidence that the Galectin-9/TIM-3 pathway plays an important role in the regulation of NK cell function, and about the modulatory role of Galectin-9 on the cytotoxicity and cytokine production of NK-92MI cells in the presence of different serum supplements. We hope that our results will aid the development of novel NK-cell-based strategies that target Galectin-9/TIM-3 checkpoint in tumors resistant to T-cell-based immunotherapy.

Antibody mediated activation of natural killer cells in malaria exposed pregnant women

Immune effector responses against Plasmodium falciparum include antibody-mediated activation of innate immune cells, which can induce Fc effector functions, including antibody-dependent cellular cytotoxicity, and the secretion of cytokines and chemokines. These effector functions are regulated by the composition of immunoglobulin G (IgG) Fc N-linked glycans. However, a role for antibody-mediated natural killer (NK) cells activation or Fc N-linked glycans in pregnant women with malaria has not yet been established. Herein, we studied the capacity of IgG antibodies from pregnant women, with placental malaria or non-placental malaria, to induce NK cell activation in response to placental malaria-associated antigens DBL2 and DBL3. Antibody-mediated NK cell activation was observed in pregnant women with malaria, but no differences were associated with susceptibility to placental malaria. Elevated anti-inflammatory glycosylation patterns of IgG antibodies were observed in pregnant women with or without malaria infection, which were not seen in healthy non-pregnant controls. This suggests that pregnancy-associated anti-inflammatory Fc N-linked glycans may dampen the antibody-mediated activation of NK cells in pregnant women with malaria infection. Overall, although anti-inflammatory glycans and antibody-dependent NK cell activation were detected in pregnant women with malaria, a definitive role for these antibody features in protecting against placental malaria remains to be proven.

Parity-related variation in cortisol concentrations in hair during pregnancy

Objective

To investigate hair cortisol concentrations (HCC) monthly in pregnant women and to explore the effect of parity.

Design

Prospective cohort study from gestational week (GW) 26, at childbirth and postpartum.

Setting

An antenatal care clinic in southeast Sweden.

Sample

390 pregnant women.

Methods

Cortisol was measured using radioimmunoassay in methanol extracts of ground hair samples.

Main outcome measures

Hair cortisol concentrations.

Results

Both primi‐ and multiparae exhibited an increase in HCC throughout pregnancy. Primiparae had significantly higher HCC in the latter part of the last trimester compared with multiparae (1 month P = 0.003, 2 months P = 0.038). The use of psychotropic medication in the first trimester correlated to HCC postpartum (P < 0.001). HCC in GW 14–17 was associated with HCC in GW 18–21 (primiparae and multiparae, P < 0.001), GW 22–25 (primiparae P = 0.036, multiparae P = 0.033), and 2 months postpartum (primiparae P = 0.049). HCC in GW 18–21 was associated with GW 22–25 in both primiparae (P < 0.001) and multiparae (P < 0.001) as well as 2 months prior to childbirth among primiparae (<0.037). In general, all estimates of HCC in pregnancy and postpartum showed a significant association between HCC for a specific month and the HCC in the previous month (all P < 0.001), except for the association of HCC among primiparae in GW 22–25 and 3 months prior to childbirth.

Conclusions

Increased cortisol concentrations in hair were observed during pregnancy, which decreased 3 months prior to childbirth in multiparae. The results indicate a quicker suppression of the hypothalamic CRH (corticotropin‐releasing hormone) production by placenta CRH in multiparous women.

Tweetable abstract

Multiparae have a quicker suppression of hypothalamic CRH production by placenta CRH during pregnancy compared to primiparae.

Multiparae have a quicker suppression of hypothalamic CRH production by placenta CRH during pregnancy compared with primiparae.

Sleep Disturbance during Infection Compromises Tfh Differentiation and Impacts Host Immunity

Although the influence of sleep quality on the immune system is well documented, the mechanisms behind its impact on natural host immunity remain unclear. Meanwhile, it has been suggested that neuroimmune interactions play an important role in this phenomenon. To evaluate the impact of stress-induced sleep disturbance on host immunity, we used a murine model of rapid eye movement sleep deprivation (RSD) integrated with a model of malaria blood-stage infection. We demonstrate that sleep disturbance compromises the differentiation of T follicular helper cells, increasing host susceptibility to the parasite. Chemical inhibition of glucocorticoid (Glcs) synthesis showed that abnormal Glcs production compromised the transcription of Tfh-associated genes resulting in impaired germinal center formation and humoral immune response. Our data demonstrate that RSD-induced abnormal activation of the hypothalamic-pituitary-adrenal axis drives host susceptibility to infection. Understanding the impact of sleep quality in natural resistance to infection may provide insights for disease management.

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REM sleep deprivation (RSD) worsens malaria induced by Plasmodium yoelii infection

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RSD decreases germinal center formation and impairs specific antibody production

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Exacerbated glucocorticoid production impairs T lymphocyte differentiation

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The relationship between sleep and immunity is a target for malaria management

Innate immune responses to malaria-infected erythrocytes in pregnant women: Effects of gravidity, malaria infection, and geographic location

BACKGROUND

Malaria in pregnancy causes maternal, fetal and neonatal morbidity and mortality, and maternal innate immune responses are implicated in pathogenesis of these complications. The effects of malaria exposure and obstetric and demographic factors on the early maternal immune response are poorly understood.

METHODS

Peripheral blood mononuclear cell responses to Plasmodium falciparum-infected erythrocytes and phytohemagglutinin were compared between pregnant women from Papua New Guinea (malaria-exposed) with and without current malaria infection and from Australia (unexposed). Elicited levels of inflammatory cytokines at 48 h and 24 h (interferon γ, IFN-γ only) and the cellular sources of IFN-γ were analysed.

RESULTS

Among Papua New Guinean women, microscopic malaria at enrolment did not alter peripheral blood mononuclear cell responses. Compared to samples from Australia, cells from Papua New Guinean women secreted more inflammatory cytokines tumor necrosis factor-α, interleukin 1β, interleukin 6 and IFN-γ; p<0.001 for all assays, and more natural killer cells produced IFN-γ in response to infected erythrocytes and phytohemagglutinin. In both populations, cytokine responses were not affected by gravidity, except that in the Papua New Guinean cohort multigravid women had higher IFN-γ secretion at 24 h (p = 0.029) and an increased proportion of IFN-γ+ Vδ2 γδ T cells (p = 0.003). Cytokine levels elicited by a pregnancy malaria-specific CSA binding parasite line, CS2, were broadly similar to those elicited by CD36-binding line P6A1.

CONCLUSIONS

Geographic location and, to some extent, gravidity influence maternal innate immunity to malaria.

Contributions of natural killer cells to the immune response against Plasmodium

Natural killer (NK) cells are important innate effector cells that are well described in their ability to kill virally-infected cells and tumors. However, there is increasing appreciation for the role of NK cells in the control of other pathogens, including intracellular parasites such as Plasmodium, the cause of malaria. NK cells may be beneficial during the early phase of Plasmodium infection—prior to the activation and expansion of antigen-specific T cells—through cooperation with myeloid cells to produce inflammatory cytokines like IFNγ. Recent work has defined how Plasmodium can activate NK cells to respond with natural cytotoxicity, and inhibit the growth of parasites via antibody-dependent cellular cytotoxicity mechanisms (ADCC). A specialized subset of adaptive NK cells that are negative for the Fc receptor γ chain have enhanced ADCC function and correlate with protection from malaria. Additionally, production of the regulatory cytokine IL-10 by NK cells prevents overt pathology and death during experimental cerebral malaria. Now that conditional NK cell mouse models have been developed, previous studies need to be reevaluated in the context of what is now known about other immune populations with similarity to NK cells (i.e., NKT cells and type I innate lymphoid cells). This brief review summarizes recent findings which support the potentially beneficial roles of NK cells during Plasmodium infection in mice and humans. Also highlighted are how the actions of NK cells can be explored using new experimental strategies, and the potential to harness NK cell function in vaccination regimens.

Molecular Principles of Intrauterine Growth Restriction in Plasmodium Falciparum Infection

Malaria in pregnancy still constitutes a particular medical challenge in tropical and subtropical regions. Of the five Plasmodium species that are pathogenic to humans, infection with Plasmodium falciparum leads to fulminant progression of the disease with massive impact on pregnancy. Severe anemia of the mother, miscarriage, stillbirth, preterm delivery and intrauterine growth restriction (IUGR) with reduced birth weight are frequent complications that lead to more than 10,000 maternal and 200,000 perinatal deaths annually in sub-Saharan Africa alone. P. falciparum can adhere to the placenta via the expression of the surface antigen VAR2CSA, which leads to sequestration of infected erythrocytes in the intervillous space. This process induces a placental inflammation with involvement of immune cells and humoral factors. Especially, monocytes get activated and change the release of soluble mediators, including a variety of cytokines. This proinflammatory environment contributes to disorders of angiogenesis, blood flow, autophagy, and nutrient transport in the placenta and erythropoiesis. Collectively, they impair placental functions and, consequently, fetal growth. The discovery that women in endemic regions develop a certain immunity against VAR2CSA-expressing parasites with increasing number of pregnancies has redefined the understanding of malaria in pregnancy and offers strategies for the development of vaccines. The following review gives an overview of molecular processes in P. falciparum infection in pregnancy which may be involved in the development of IUGR.

Maternal parity and perinatal cortisol adaptation: The role of pregnancy-specific distress and implications for postpartum mood

INTRODUCTION

Compared to women who have given birth before (i.e., multiparas), those giving birth for the first time (i.e., primiparas) show higher cortisol levels. Psychological factors may play a role; hypothalamic-pituitary-adrenal activation is a well-described stress response. Primiparity also predicts greater risk for postpartum depression, which may be related to greater correspondence between cortisol and mood following prenatal cortisol elevations. The current study examined associations among parity, perinatal cortisol adaptation, pregnancy-specific distress, and postpartum mood.

METHODS

This longitudinal study assayed serum cortisol levels among 137 women at early, mid-, and late pregnancy and postpartum. Pregnancy-specific distress and depressive symptoms were assessed. Maternal age, race, body mass index, sleep quality, depressive symptoms, and sampling time of day were statistically controlled.

RESULTS

Primiparous women showed higher cortisol levels than multiparous women during mid- (χ² = 11.8, p < 0.01) and late pregnancy (χ² = 18.9, p < 0.01) and higher distress across pregnancy (F_1,126 = 22.1, p < 0.01). Mediation analyses demonstrated that the association between parity and prenatal cortisol (per area under the curve; AUC) was partially accounted for by distress (ab = 1.0, 95%CI [0.05, 2.9]). Prenatal cortisol (per AUC) did not predict postpartum depressive symptoms (b* = 0.03, p = 0.81), with no difference by parity (b* = 0.03, p = 0.91). At postpartum, a significant interaction between parity and cortisol (b* = 0.40, p = 0.03) revealed no significant association between cortisol and mood among multiparas (b* = -0.11, p = 0.28) but a trend toward a positive association among primiparas (b* = 0.24, p = 0.06).

DISCUSSION

Cortisol levels and pregnancy-specific distress are higher in primiparas versus multiparas, with pregnancy-specific distress partially mediating the association between parity and cortisol levels. Cortisol levels and mood display correspondence at postpartum in primiparous but not multiparous women. While observational studies must be interpreted with caution due to potential unmeasured confounders, these findings suggest that future studies examining mechanisms underlying perinatal and postpartum hypothalamic-pituitary-adrenal perturbations and designing interventions aimed at preventing related complications should carefully consider potential differences by parity.

Microvesicles from malaria-infected red blood cells activate natural killer cells via MDA5 pathway

Natural killer (NK) cells provide the first line of defense against malaria parasite infection. However, the molecular mechanisms through which NK cells are activated by parasites are largely unknown, so is the molecular basis underlying the variation in NK cell responses to malaria infection in the human population. Here, we compared transcriptional profiles of responding and non-responding NK cells following exposure to Plasmodium-infected red blood cells (iRBCs) and identified MDA5, a RIG-I-like receptor involved in sensing cytosolic RNAs, to be differentially expressed. Knockout of MDA5 in responding human NK cells by CRISPR/cas9 abolished NK cell activation, IFN-γ secretion, lysis of iRBCs. Similarly, inhibition of TBK1/IKKε, an effector molecule downstream of MDA5, also inhibited activation of responding NK cells. Conversely, activation of MDA5 by liposome-packaged poly I:C restored non-responding NK cells to lyse iRBCs. We further show that microvesicles containing large parasite RNAs from iRBCs activated NK cells by fusing with NK cells. These findings suggest that NK cells are activated through the MDA5 pathway by parasite RNAs that are delivered to the cytoplasm of NK cells by microvesicles from iRBCs. The difference in MDA5 expression between responding and non-responding NK cells following exposure to iRBCs likely contributes to the variation in NK cell responses to malaria infection in the human population.

Malaria is an important parasitic disease with a major public health concern. Malaria pathogenesis involves a complex interplay between parasitic and host factors. A better understanding of early host response and the determinants of immunity are essential to developing innovative therapeutic approaches. Natural killer (NK) cells are important immune cells in protection against malaria infection but show significant differences in their responses in the human population. Here we analyze the differences between human NK cells that respond to and don’t respond to malaria infection. We found that human NK cells that respond to malaria-infected red blood cells (iRBC) have higher levels of a pathogen recognition receptor, MDA5. This receptor is activated by small vesicles released from iRBC. By activating MDA5 with a small molecule agonist, we can improve non-responder NK cells to clear iRBC. Our study provides new insights into the mechanism by which NK cells control malaria infection and possible NK cell-based intervention of malaria infection in human.

Beyond genome-wide scan: Association of a cis-regulatory NCR3 variant with mild malaria in a population living in the Republic of Congo

Linkage studies have revealed a linkage of mild malaria to chromosome 6p21 that contains the NCR3 gene encoding a natural killer cell receptor, whereas NCR3-412G>C (rs2736191) located in its promoter region was found to be associated with malaria in Burkina Faso. Here we confirmed the association of rs2736191 with mild malaria in a Congolese cohort and investigated its potential cis-regulatory effect. Luciferase assay results indicated that rs2736191-G allele had a significantly increased promoter activity compared to rs2736191-C allele. Furthermore, EMSAs demonstrated an altered binding of two nuclear protein complexes to the rs2736191-C allele in comparison to rs2736191-G allele. Finally, after in silico identification of transcription factor candidates, pull-down western blot experiments confirmed that both STAT4 and RUNX3 bind the region encompassing rs2736191 with a higher affinity for the G allele. To our knowledge, this is the first report that explored the functional role of rs2736191. These results support the hypothesis that genetic variation within natural killer cell receptors alters malaria resistance in humans.

Undernutrition and malaria in pregnancy - a dangerous dyad?

BACKGROUND

In low-resource settings, malaria and macronutrient undernutrition are major health problems in pregnancy, contributing significantly to adverse pregnancy outcomes such as preterm birth and fetal growth restriction. Affected pregnancies may result in stillbirth and neonatal death, and surviving children are at risk of poor growth and infection in infancy, and of non-communicable diseases in adulthood. Populations exposed to macronutrient undernutrition frequently reside in malaria-endemic areas, and seasonal peaks of low food supply and malaria transmission tend to coincide. Despite these geographic and temporal overlaps, integrated approaches to these twin challenges are infrequent.

DISCUSSION

This opinion article examines the current evidence for malaria-macronutrition interactions and discusses possible mechanisms whereby macronutrient undernutrition and malaria may interact to worsen pregnancy outcomes. Macronutrient undernutrition dysregulates the immune response. In pregnant women, undernutrition may worsen the already increased susceptibility to malarial infection and could impair development of protective immunity to malaria, and is likely to exacerbate the impact of placental malaria on fetal growth. Malarial infection, in turn, can drive nutritional depletion; poor gestational weight gain and weight loss in pregnancy increases the risk of adverse pregnancy outcomes. Despite a commendable number of studies and trials that, in isolation, attempt to address the challenges of malaria and undernutrition in pregnancy, few dare to venture beyond the 'single disease - single solution' paradigm. We believe that this may be a lost opportunity: researching malaria-nutrition interactions, and designing and implementing integrated interventions to prevent and treat these commonly co-existing and intertwining conditions, may markedly reduce the high burden of preterm birth and fetal growth restriction in affected areas.

CONCLUSION

We call for more collaboration between researchers studying malaria and nutrition in pregnancy, and propose a research agenda to address this important twin health problem.

Malaria and immunity during pregnancy and postpartum: a tale of two species

It is well established that pregnant women are at an increased risk of Plasmodium falciparum infection when compared to non-pregnant individuals and limited epidemiological data suggest Plasmodium vivax risk also increases with pregnancy. The risk of P. falciparum declines with successive pregnancies due to the acquisition of immunity to pregnancy-specific P. falciparum variants. However, despite similar declines in P. vivax risk with successive pregnancies, there is a paucity of evidence P. vivax-specific immunity. Cross-species immunity, as well as immunological and physiological changes that occur during pregnancy may influence the susceptibility to both P. vivax and P. falciparum. The period following delivery, the postpartum period, is relatively understudied and available epidemiological data suggests that it may also be a period of increased risk of infection to Plasmodium spp. Here we review the literature and directly compare and contrast the epidemiology, clinical pathogenesis and immunological features of P. vivax and P. falciparum in pregnancy, with a particular focus on studies performed in areas co-endemic for both species. Furthermore, we review the intriguing epidemiology literature of both P. falciparum and P. vivax postpartum and relate observations to the growing literature pertaining to malaria immunology in the postpartum period.

Peripheral blood cell signatures of Plasmodium falciparum infection during pregnancy

Sequestration of Plasmodium falciparum-infected erythrocytes in placental intervillous spaces causes inflammation and pathology. Knowledge of the profiles of immune cells associated with the physiopathology of pregnancy-associated malaria (PAM) is scarce. We conducted a longitudinal, prospective study, both in Benin and Tanzania, including ∼1000 pregnant women in each site with systematic follow-up at scheduled antenatal visits until delivery. We used ex vivo flow cytometry to identify peripheral blood mononuclear cell (PBMC) profiles that are associated with PAM and anaemia, determining the phenotypic composition and activation status of PBMC in selected sub-groups with and without PAM both at inclusion and at delivery in a total of 302 women. Both at inclusion and at delivery PAM was associated with significantly increased frequencies both of B cells overall and of activated B cells. Infection-related profiles were otherwise quite distinct at the two different time-points. At inclusion, PAM was associated with anaemia, with an increased frequency of immature monocytes and with a decreased frequency of regulatory T cells (Treg). At delivery, infected women presented with significantly fewer plasmacytoid dendritic cells (DC), more myeloid DC expressing low levels of HLA-DR, and more effector T cells (Teff) compared to uninfected women. Independent associations with an increased risk of anaemia were found for altered antigen-presenting cell frequencies at inclusion, but for an increased frequency of Teff at delivery. Our findings emphasize the prominent role played by B cells during PAM whenever it arises during pregnancy, whilst also revealing signature changes in other circulating cell types that, we conclude, primarily reflect the relative duration of the infections. Thus, the acute, recently-acquired infections present at delivery were marked by changes in DC and Teff frequencies, contrasting with infections at inclusion, considered chronic in nature, that were characterized by an abundance of immature monocytes and a paucity of Treg in PBMC.

Prospects and Pitfalls of Pregnancy-Associated Malaria Vaccination Based on the Natural Immune Response to Plasmodium falciparum VAR2CSA-Expressing Parasites

Pregnancy-associated malaria, a manifestation of severe malaria, is the cause of up to 200,000 infant deaths a year, through the effects of placental insufficiency leading to growth restriction and preterm delivery. Development of a vaccine is one strategy for control. Plasmodium falciparum-infected red blood cells accumulate in the placenta through specific binding of pregnancy-associated parasite variants that express the VAR2CSA antigen to chondroitin sulphate A on the surface of syncytiotrophoblast cells. Parasite accumulation, accompanied by an inflammatory infiltrate, disrupts the cytokine balance of pregnancy with the potential to cause placental damage and compromise foetal growth. Multigravid women develop immunity towards VAR2CSA-expressing parasites in a gravidity-dependent manner which prevents unfavourable pregnancy outcomes. Although current vaccine design, targeting VAR2CSA antigens, has succeeded in inducing antibodies artificially, this candidate may not provide protection during the first trimester and may only protect those women living in areas endemic for malaria. It is concluded that while insufficient information about placental-parasite interactions is presently available to produce an effective vaccine, incremental progress is being made towards achieving this goal.

Malaria in pregnancy: small babies, big problem

Placental malaria is hypothesized to lead to placental insufficiency, which causes fetal growth restriction (FGR). In this review, recent discoveries regarding the mechanisms of pathogenesis by which malaria causes FGR are discussed in the wider context of placental function and fetal growth. Placental malaria and associated host responses can induce changes in placental structure and function, affecting pregnancy-associated growth-regulating hormones and predisposing the offspring to hypertension and vascular dysfunction. Risk factors associated with FGR are highlighted, and potential interventions and studies to uncover remaining mechanisms of pathogenesis are proposed. Together, these strategies aim to decrease the burden of FGR associated with malaria in pregnancy.

Trichomonas vaginalis: dehydroepiandrosterone sulfate and 17beta-estradiol alter NTPDase activity and gene expression

We investigated the effect of dehydroepiandrosterone sulfate (DHEAS) and 17beta-estradiol on NTPDase activity in fresh clinical (VP60) and long-term-grown (30236 ATCC) isolates of Trichomonas vaginalis followed by NTPDase gene transcriptional analysis. ATP hydrolysis was activated in vitro by 17beta-estradiol (0.01-1.0microM) in the VP60 isolate. Treatment for 2h with 17beta-estradiol (0.01-1microM) promoted an inhibition in nucleotide hydrolysis in the 30236 isolate whereas the 12h-treatment promoted an activation of nucleotide hydrolysis in both isolates. ADP hydrolysis was inhibited in vitro by 1.0-5.0microM DHEAS in the ATCC isolate. The treatment with DHEAS (0.01-1.0microM) for 2h inhibited ATP and ADP hydrolysis in VP60; however, during a 12h-treatment with DHEAS, nucleotide hydrolysis was inhibited in both isolates. Two NTPDase orthologous (NTPDaseA and NTPDaseB) were identified and the treatment with DHEAS for 12h was able to inhibit mRNA NTPDaseA transcript levels from the VP60. These findings demonstrate that NTPDase activity and gene expression pattern are modulated by exposure to steroids in T. vaginalis.

Cortisol, prolactin, cytokines and the susceptibility of pregnant Sudanese women to Plasmodium falciparum malaria

Understanding the hormonal and cytokine interactions that underlie susceptibility to the disease should be helpful in elucidating the pathogenesis of malaria during pregnancy. The current study was conducted in the Wad Medani hospital, in an area of central Sudan that is characterised by unstable malarial transmission. Its aims were to investigate the roles and interactions of cortisol, prolactin, interferon-gamma (IFN-gamma), interleukin-4 (IL-4) and interleukin-10 (IL-10) in pregnant women with Plasmodium falciparum malaria. The 82 pregnant subjects who were enrolled either had uncomplicated, P. falciparum malaria (the 47 cases) or were apparently uninfected and healthy women (the 37 controls) who were similar to the cases in terms of their mean age, weight, gravidity, gestational age and haemoglobin concentration. Compared with the controls, the cases were found to have significantly higher serum concentrations of total cortisol and IL-10 and significantly lower levels of prolactin and IFN-gamma (but similar concentrations of IL-4). The hormone and cytokine concentrations measured in the infected primigravidae were similar to those recorded in the infected multigravidae. Among the cases, there was a significant positive correlation between serum cortisol and IL-10 (r=0.188; P=0.025) and significant negative correlations between prolactin and both IL-4 (r=-0.175; P=0.038) and IL-10 (r=-0.186; P=0.027) but no significant correlation between prolactin and cortisol. During pregnancy, immune responses appear to be influenced by P. falciparum infections, irrespective of parity. Cortisol, prolactin and some cytokines appear to be key mediators in the host response to P. ?falciparum infection, although further research on this subject is clearly needed.

Natural killer cell IFN-gamma-activity is associated with Plasmodium falciparum infection during pregnancy

The ability of natural killer (NK) cells to produce gamma interferon (IFN-gamma) after ex vivo stimulation with crude schizont lysate of Plasmodium falciparum was studied in uninfected and P. falciparum-infected pregnant Gabonese women segregated according to the gravidity at the time of delivery. This activity was measured in purified NK cells as well as in whole blood from the periphery and cord. Crude schizont lysate-stimulated NK cells from primiparous women produced significantly more IFN-gamma than those from multiparous women (P<0.001). Women with malaria infection produced more IFN-gamma than negative women in peripheral blood (P<0.001) indicating that immunological determinants regulating the susceptibility to malaria in pregnant women are parasite-specific. These findings reveal that NK cells are major source of IFN-gamma when exposed to P. falciparum antigens in vitro in absence of any other co-stimulant.

Influence of human chorionic gonadotropin (hCG) on in vitro growth of Plasmodium falciparum

BACKGROUND

During pregnancy, women are more susceptible to Plasmodium falciparum infections and frequently have a higher parasitaemia than non-pregnant women. Several mechanisms are responsible for their increased susceptibility, including down-modulation of immune responses that aid in parasite clearance and sequestration of infected erythrocytes in the placenta. Early in pregnancy, a third mechanism may contribute to higher parasitaemia, since it has been reported that addition of human chorionic gonadotropin (hCG) to in vitro cultures of the NF54-strain of P. falciparum results in increased parasite growth rates. The goal of this study was to further examine the effect of hCG on P. falciparum growth.

METHODS

The NF54-3D7, FVO and 7G8 strains of P. falciparum were cultured in vitro with various physiological concentrations of hCG purchased from three sources. Infected erythrocytes were also co-cultured with a human cell line that naturally secretes hCG.

RESULTS

Results from 14 experiments using different combinations of parasite strains and concentrations of hCG from different sources, as well as the co-culture studies, failed to provide convincing evidence that hCG enhances parasite growth in vitro.

CONCLUSION

Based on these data, it seems unlikely that hCG has a direct effect on the rate of parasite growth early in pregnancy.

Plasmodium falciparum during pregnancy: a puzzling parasite tissue adhesion tropism

P. falciparum malaria severely affects pregnant women and children. Despite immunity through lifelong exposure to malaria, pregnant women become susceptible to infections causing anaemia, abortions and low birth weight. They experience massive accumulation of infected erythrocytes (IEs) in the placenta. Adhesion of IEs to host endothelial receptors is mediated by members of a large diverse protein family called P. falciparum erythrocyte membrane protein 1 (PfEMP1). Pregnancy malaria is generally associated with the emergence of a distinct subset of parasites expressing a unique PfEMP1 that binds to the host-receptor chondroitin sulfate A (CSA). Resistance to pregnancy malaria is associated with the acquisition of antibodies that block IEs binding to placental CSA. The absence (or rare occurrence) of CSA-binding parasites in malaria patients (children, men and non-pregnant women) suggests that these parasites become virulent only during pregnancy. The molecular mechanisms used by P. falciparum to achieve the timely expression of the Pf-CSA ligand in pregnant women remain puzzling. In this review we will discuss two hypothetical mechanisms by which CSA-binding parasites may arise during pregnancy. The first, a selection process by the placenta of a distinct sub-population of P. falciparum expressing a particular PfEMP1. The second, an induction mechanism that facilitates the expression of a particular PfEMP1 protein by specific host factor(s) present only during pregnancy.

Malaria in pregnancy: pathogenesis and immunity

Understanding of the biological basis for susceptibility to malaria in pregnancy was recently advanced by the discovery that erythrocytes infected with Plasmodium falciparum accumulate in the placenta through adhesion to molecules such as chondroitin sulphate A. Antibody recognition of placental infected erythrocytes is dependent on sex and gravidity, and could protect from malaria complications. Moreover, a conserved parasite gene-var2csa-has been associated with placental malaria, suggesting that its product might be an appropriate vaccine candidate. By contrast, our understanding of placental immunopathology and how this contributes to anaemia and low birthweight remains restricted, although inflammatory cytokines produced by T cells, macrophages, and other cells are clearly important. Studies that unravel the role of host response to malaria in pathology and protection in the placenta, and that dissect the relation between timing of infection and outcome, could allow improved targeting of preventive treatments and development of a vaccine for use in pregnant women.

Placental Plasmodium falciparum infection: causes and consequences of in utero sensitization to parasite antigens

Available evidence suggests that, in African populations, systemic blood-dwelling parasitoses of mothers are associated with enhanced susceptibility to infection of their offspring. Thus, children born to mothers with filariasis or schistosomiasis are infected earlier, and offspring of mothers with placental Plasmodium falciparum at delivery, commonly referred to as pregnancy-associated malaria or PAM, are themselves at higher risk of developing parasitaemia during infancy. Since foetal/neonatal antigen-presenting cells (APC) are either immature or provide insufficient costimulatory signals to T cells, thus favouring tolerance induction, it is commonly assumed that soluble parasite components [protein antigens], transferred transplacentally and inducing foetal immune tolerance, are largely, if not exclusively, responsible for these outcomes. Plasmodial asexual blood stage antigen-specific T cells are detectable in as many as two-thirds of all cord blood samples in malaria-endemic countries of sub-Saharan Africa, indicating that in utero sensitization may be a common phenomenon during pregnancy in these populations. Parasite antigen-specific T cell responses of neonates born to helminth-infected mothers display a highly skewed Th2-type cytokine pattern, with a prominent role for the regulatory cytokine interleukin (IL)-10. Similarly, the cord blood immune response of those born to mothers identified with on-going PAM is characterised by inducible parasite antigen-specific IL-10-producing regulatory T cells that can inhibit both APC HLA expression and Th1-type T cell responses. In contrast, plasmodial antigen-specific Th1-type responses, characterised by IFN-gamma production, predominate in cord blood of those born to mothers successfully treated for Pf malaria during gestation, suggesting that the duration and/or the nature of antigen exposure in utero governs the outcome with respect to neonatal immune responses. Aspects of APC function in the context of these differentially modulated responses, whether and how the latter translate into altered susceptibility to Pf infection during infancy, as well as the possible implications for vaccination in early life, are aspects that are discussed in this review.

Some aspects of the behavior of the hypothalamus-pituitary-adrenal axis in patients with uncomplicated Plasmodium falciparum malaria: Cortisol and dehydroepiandrosterone levels

We studied the behavior of cortisol and dehydroepiandrosterone (DHEA) in 24 patients with uncomplicated Plasmodium falciparum malaria of the Evandro Chagas Institute, Belém, Pará, Brazil. The patients were evaluated before treatment (Day 0), 24h after the beginning of medication (Day 1) and on Day 8 of follow-up (Day 7). Steroid levels were correlated with parasitemia, temperature and time of the disease. The levels of these hormones were found to be significantly higher on Day 0 than on Day 7, showing no correlation with parasitemia or temperature, but temperature had a positive effect on the correlation between cortisol and dehydroepiandrosterone. Cortisol was not correlated with the time of disease, but a significant negative correlation was observed between DHEA and time of disease on Day 7, suggesting a decline in the adrenal reserve of this steroid. In conclusion, an increase in cortisol and dehydroepiandrosterone is observed in patients with falciparum malaria, with these levels declining with decreasing parasitemia. The finding that temperature interfered with the correlation between cortisol and dehydroepiandrosterone suggests a common mechanism for the activation of these hormones in malaria.

Interactions between natural killer cells, cortisol and prolactin in malaria during pregnancy

Natural killer cells derived from pluripotent hematopoietic stem cells are important cells of the immune system that have two main functions: a cytolytic activity and a cytokine-producing capacity. These functions are tightly regulated by numerous activating and inhibitory receptors, including newly discovered receptors that selectively trigger the cytolytic activity in a major histocompatibility complex independent manner. Based on their defining function of spontaneous cytotoxicity without prior immunization, natural killer (NK) cells have been thought to play a critical role in immune surveillance and cancer therapy. New insights into NK cell biology have suggested their major roles in the control of infections, particularly in Plasmodium falciparum infection and in fetal implantation. P. falciparum is the main protozoan parasite responsible for malaria causing 200-300 million clinical cases and killing over 3 million people each year. This review provides an update on NK cell function, ontogeny and biology in order to better understand the role of NK cells in pregnancy in regions where malaria is endemic. Understanding mechanisms of NK cell functions may lead to novel therapeutic strategies for the treatment of human disease, in general, and particularly in the fight against malaria.

The protozoan Neospora caninum directly triggers bovine NK cells to produce gamma interferon and to kill infected fibroblasts

Natural killer (NK) cells are considered to be key players in the early innate responses to protozoan infections, primarily indirectly by producing gamma interferon (IFN-gamma) in response to cytokines, like interleukin 12 (IL-12). We demonstrate that live, as well as heat-inactivated, tachyzoites of Neospora caninum, a Toxoplasma-like protozoan, directly trigger production of IFN-gamma from purified, IL-2-activated bovine NK cells. This response occurred independently of IL-12 but was increased by the addition of the cytokine. A similar IFN-gamma response was measured in cocultures of NK cells and N. caninum-infected autologous fibroblasts. However, no NK cell-derived IFN-gamma response was detected when cells were cultured with soluble antigens from the organism, indicating that intact tachyzoites or nonsoluble components are necessary for NK cell triggering. Furthermore, N. caninum-infected autologous fibroblasts had increased susceptibility to NK cell cytotoxicity compared to uninfected fibroblasts. This cytotoxicity was largely mediated by a perforin-mediated mechanism. The activating receptor NKp46 was involved in cytotoxicity against fibroblasts but could not explain the increased cytotoxicity against infected targets. Interestingly, N. caninum tachyzoites were able to infect cultured NK cells, in which tachyzoites proliferated inside parasitophorous vacuoles. Together, these findings underscore the role of NK cells as primary responders during a protozoan infection, describe intracellular protozoan infection of NK cells in vitro for the first time, and represent the first functional study of purified bovine NK cells in response to infection.

The immunology and pathogenesis of malaria during pregnancy

Women in endemic areas become highly susceptible to malaria during first and second pregnancies, despite immunity acquired after years of exposure. Recent insights have advanced our understanding of pregnancy malaria caused by Plasmodium falciparum, which is responsible for the bulk of severe disease and death. Accumulation of parasitized erythrocytes in the blood spaces of the placenta is a key feature of maternal infection with P. falciparum. Placental parasites express surface ligands and antigens that differ from those of other P. falciparum variants, facilitating evasion of existing immunity, and mediate adhesion to specific molecules, such as chondroitin sulfate A, in the placenta. The polymorphic and clonally variant P. falciparum erythrocyte membrane protein 1, encoded by var genes, binds to placental receptors in vitro and may be the target of protective antibodies. An intense infiltration of immune cells, including macrophages, into the placental intervillous spaces, and the production of pro-inflammatory cytokines often occur in response to infection, and are associated with low birth weight and maternal anemia. Expression of alpha and beta chemokines may initiate or facilitate this cellular infiltration during placental malaria. Specific immunity against placental-binding parasites may prevent infection or facilitate clearance of parasites prior to the influx of inflammatory cells, thereby avoiding a cascade of events leading to disease and death. Much less is known about pathogenic processes in P. vivax infections, and corresponding immune responses. Emerging knowledge of the pathogenesis and immunology of malaria in pregnancy will increasingly lead to new opportunities for the development of therapeutic and preventive interventions and new tools for diagnosis and monitoring.

Estradiol, but not dehydroepiandrosterone, decreases parasitemia and increases the incidence of cerebral malaria and the mortality in plasmodium berghei ANKA-infected CBA mice

OBJECTIVE

The effect of castration and subsequent replacement of dehydroepiandrosterone (DHEA) or estradiol on parasitemia, mortality and incidence of cerebral malaria (CM) was evaluated in CBA mice infected with Plasmodium berghei ANKA.

METHODS

Female mice were castrated, and groups of 12-15 animals received daily injections of DHEA, estradiol or saline. Four days after the start of treatment, mice were inoculated with 1 x 10(6)P. berghei ANKA-parasitized erythrocytes. DHEA treatment was continued during the 5 days after infection, and estradiol was administered during the follow-up. Parasitemia was evaluated daily in Giemsa-stained blood smears. Signs of CM were determined by the manifestation of coma, limb paralysis and/or convulsions. Plasma TNF-alpha levels were evaluated by sandwich ELISA. Nitric oxide synthase (NOS) activity in the brain of moribund mice was measured by the method of Bredt and Snyder.

RESULTS

In non-castrated infected mice, the incidence of CM was 50%, and plasma TNF-alpha increased and brain NOS activity decreased compared to non-infected controls. Castration had no major effect on the parameters analyzed (parasitemia, mortality, CM incidence, TNF-alpha levels or NOS activity). Estradiol replacement caused a decrease in parasitemia but resulted in higher CM incidence and faster mortality, with an increase in NOS activity.

CONCLUSIONS

Estradiol modulated the immune response of P. berghei ANKA-infected CBA mice, decreasing parasitemia and increasing NOS activity, and impacted negatively on survival and CM incidence, showing that neuroimmunoendocrine interactions are important in the physiopathogenesis of malaria infections.

Hypothalamic-pituitary gonadal axis and immune response imbalance during chronic filarial infections

Bi-directional relationships operate between the hypothalamic-pituitary-gonadal axis and the immune system. Cytokines, peptide hormones and their shared receptors/ligands are used as a common biological language for communication within and between the immune and neuroendocrine systems. Such communication suggests an immunoregulatory role for the brain and a sensory function for the immune system. We used a radioimmunoassay to measure the concentrations of steroid hormones (cortisol, testosterone, estradiol and progesterone) and pituitary hormones [follicle stimulating hormone (FSH), luteinizing hormone (LH) human chorionic gonadotropin (HCG) and prolactin] in peripheral blood plasma from 78 young Gabonese women with chronic filarial infections. We used an enzyme-linked immunosorbent assay to determine the concentrations of four proinflammatory cytokines [tumor necrosis factor-alpha (TNF-alpha), gamma interferon (IFN-gamma), interleukin-1 (IL-1) and IL-6] in the same plasma samples. Progesterone was unchanged and all other steroid hormone plasma concentrations were lower in microfilaremic women than in amicrofilaremic women. The concentration of LH was higher in amicrofilaremic women, whereas the prolactin concentration was higher in microfilaremics. The plasma concentrations of TNF-alpha, IFN-gamma, IL-1 and IL-6 were higher in microfilaremic women. A strong negative correlation was found between the steroid and pituitary hormones and the pro-inflammatory cytokines. Conversely, a strong positive correlation was found between prolactin and the same cytokines. These data provide first evidence of immune system and hormonal system disturbance during chronic filarial infections and suggest that the observed imbalance should be taken into account in the diagnosis and treatment of filarial infections.

Modulation of immune responses during HIV-malaria co-infection in pregnancy

Infection with either HIV or malaria during pregnancy often results in adverse outcomes for mother and child. Co-infection further increases the risks of these events, which include maternal anemia and babies with low birth weight. The immunological bases for the increased susceptibility of HIV-infected mothers to malaria and for the effect of co-infection on mother-to-child transmission of HIV are areas of major importance in public health. In this article, we review current data about humoral and cellular responses to HIV-placental-malaria co-infection and present an immunological hypothesis to explain the epidemiological findings.

Effects of prolactin and cortisol on natural killer (NK) cell surface expression and function of human natural cytotoxicity receptors (NKp46, NKp44 and NKp30)

The surface density of the triggering receptors (e.g. NKp46 and NKp30) responsible for natural killer (NK) cell-mediated cytotoxicity determines the ability of NK cells to kill susceptible target cells. In this study, we show that prolactin up-regulates and cortisol down-regulates the surface expression of NKp46 and NKp30. The prolactin-mediated activation and the cortisol-mediated inhibition of natural cytotoxicity receptor (NCR) surface expression reflects gene regulation at the transcriptional level. NKp46 and NKp30 are the major receptors involved in the NK-mediated killing of K562, a human chronic myelogenous leukaemia cell line. Accordingly, the prolactin dramatically increased the NK-mediated killing of the K562 cell line, whereas cortisol abolished this activity. Our data suggest a mechanism by which prolactin activates the lytic function of NK cells, and cortisol inhibits the NK-mediated attack.

Visceral leishmaniasis in pregnancy: a case series and a systematic review of the literature

OBJECTIVES

Visceral leishmaniasis (VL) is endemic in tropical and sub-tropical areas. Only anecdotal cases of VL in pregnancy are reported in the literature, although the disease is life-threatening for both mothers and infants. Here we report a small series of pregnant women with VL observed in the Neapolitan area over a 7 year period and carry out a systematic review of the literature on this topic.

METHODS

Consecutive cases of VL in HIV-negative female patients between 1996 and 2002 were evaluated. Pregnant women who fulfilled criteria for VL diagnosis were included and diagnostic, clinical and therapeutic features were considered. The outcome for both the pregnant woman and the fetus was evaluated over a 24 month period of post-therapy follow-up. A systematic search of English language literature through the MEDLINE database and Cochrane Library with the search strings 'leishmaniasis AND pregnancy' and 'leishmaniasis AND visceral AND congenital' integrated with a manual search completed our study.

RESULTS

Five consecutive pregnant women were diagnosed as having VL. Fever and hepatosplenomegaly were the main presenting symptoms. All received liposomal amphotericin B without any toxicity to either the mothers or newborns. No treatment failure or congenital VL case was observed. The systemic review of the literature revealed 17 cases of VL during pregnancy. Untreated VL resulted in consequences on the fetus or congenital VL.

CONCLUSIONS

The efficacy and safety of amphotericin B formulations for mother and fetus are supported by the cumulative analysis of our data and literature data.

Hemozoin differentially regulates proinflammatory cytokine production in human immunodeficiency virus-seropositive and -seronegative women with placental malaria

Pregnant women are at an increased risk for malarial infection. Plasmodium falciparum accumulates in the placenta and is associated with dysregulated immune function and poor birth outcomes. Malarial pigment (hemozoin) also accumulates in the placenta and may modulate local immune function. In this study, the impact of hemozoin on cytokine production by intervillous blood mononuclear cells from malaria-infected placentas was investigated. There was a dose-dependent, suppressive effect of hemozoin on production of gamma interferon (IFN-gamma), with less of an effect on tumor necrosis factor alpha (TNF-alpha) and interleukin-10, in human immunodeficiency virus-seronegative (HIV(-)) women. In contrast, IFN-gamma and TNF-alpha production tended to increase in HIV-seropositive women with increasing hemozoin levels. Production patterns of cytokines, especially IFN-gamma in HIV(-) women, followed different trends as a function of parasite density and hemozoin level. The findings suggest that the influences of hemozoin accumulation and high-density parasitemia on placental cytokine production are not equivalent and may involve different mechanisms, all of which may operate differently in the context of HIV infection. Cytokine production dysregulated by accumulation of hemozoin or high-density parasitemia may induce pathology and impair protective immunity in HIV-infected and -uninfected women.