Lena Serghides

Disruption of CD36 impairs cytokine response to Plasmodium falciparum glycosylphosphatidylinositol and confers susceptibility to severe and fatal malaria in vivo

CD36 is a scavenger receptor that has been implicated in malaria pathogenesis as well as innate defense against blood-stage infection. Inflammatory responses to Plasmodium falciparum GPI (pfGPI) anchors are believed to play an important role in innate immune response to malaria. We investigated the role of CD36 in pfGPI-induced MAPK activation and proinflammatory cytokine secretion. Furthermore, we explored the role of this receptor in an experimental model of acute malaria in vivo. We demonstrate that ERK1/2, JNK, p38, and c-Jun became phosphorylated in pfGPI-stimulated macrophages. In contrast, pfGPI-induced phosphorylation of JNK, ERK1/2, and c-Jun was reduced in Cd36−/− macrophages and Cd36−/− macrophages secreted significantly less TNF-α in response to pfGPI than their wild-type counterparts. In addition, we demonstrate a role for CD36 in innate immune response to malaria in vivo. Compared with wild-type mice, Cd36−/− mice experienced more severe and fatal malaria when challenged with Plasmodium chabaudi chabaudi AS. Cd36−/− mice displayed a combined defect in cytokine induction and parasite clearance with a dysregulated cytokine response to infection, earlier peak parasitemias, higher parasite densities, and higher mortality rates than wild-type mice. These results provide direct evidence that pfGPI induces TNF-α secretion in a CD36-dependent manner and support a role for CD36 in modulating host cytokine response and innate control of acute blood-stage malaria infection in vivo.

C5a Enhances Dysregulated Inflammatory and Angiogenic Responses to Malaria In Vitro: Potential Implications for Placental Malaria

Background Placental malaria (PM) is a leading cause of maternal and infant mortality. Although the accumulation of parasitized erythrocytes (PEs) and monocytes within the placenta is thought to contribute to the pathophysiology of PM, the molecular mechanisms underlying PM remain unclear. Based on the hypothesis that excessive complement activation may contribute to PM, in particular generation of the potent inflammatory peptide C5a, we investigated the role of C5a in the pathogenesis of PM in vitro and in vivo. Methodology and Principal Findings Using primary human monocytes, the interaction between C5a and malaria in vitro was assessed. CSA- and CD36-binding PEs induced activation of C5 in the presence of human serum. Plasmodium falciparum GPI (pfGPI) enhanced C5a receptor expression (CD88) on monocytes, and the co-incubation of monocytes with C5a and pfGPI resulted in the synergistic induction of cytokines (IL-6, TNF, IL-1β, and IL-10), chemokines (IL-8, MCP-1, MIP1α, MIP1β) and the anti-angiogenic factor sFlt-1 in a time and dose-dependent manner. This dysregulated response was abrogated by C5a receptor blockade. To assess the potential role of C5a in PM, C5a plasma levels were measured in malaria-exposed primigravid women in western Kenya. Compared to pregnant women without malaria, C5a levels were significantly elevated in women with PM. Conclusions and Significance These results suggest that C5a may contribute to the pathogenesis of PM by inducing dysregulated inflammatory and angiogenic responses that impair placental function.

Rosiglitazone modulates the innate immune response to Plasmodium falciparum infection and improves outcome in experimental cerebral malaria.

For severe malarial syndromes such as cerebral malaria, adverse clinical outcomes are often mediated by the immune system rather than caused by the parasite directly. However, few therapeutic agents have been developed to modulate the hosts immunopathological responses to infection. Here, we report that the peroxisome proliferator-activated receptor gamma (PPARgamma) agonist rosiglitazone modulated the host response to malaria by enhancing phagocytic clearance of malaria-parasitized erythrocytes and by decreasing inflammatory responses to infection via inhibition of Plasmodium falciparum glycosylphosphatidylinositol-induced activation of the mitogen-activated protein kinase (MAPK) and nuclear factor-kappaB (NF-kappaB) signaling pathways. We found that, in the Plasmodium berghei strain ANKA experimental model of cerebral malaria, rosiglitazone modified the inflammatory response to malarial infection and improved the survival rate even when treatment was initiated as late as day 5 after infection. Furthermore, rosiglitazone reduced the parasitemia in a CD36-dependent manner in the Plasmodium chabaudi chabaudi hyperparasitemia model. These data suggest that PPARgamma agonists represent a novel class of host immunomodulatory drugs that may be useful for treatment of severe malaria syndromes.

Inhaled Nitric Oxide Reduces Endothelial Activation and Parasite Accumulation in the Brain, and Enhances Survival in Experimental Cerebral Malaria

The host immune response contributes to the onset and progression of severe malaria syndromes, such as cerebral malaria. Adjunctive immunomodulatory strategies for severe malaria may improve clinical outcome beyond that achievable with artemisinin-based therapy alone. Here, we report that prophylaxis with inhaled nitric oxide significantly reduced systemic inflammation (lower TNF, IFNγ and MCP-1 in peripheral blood) and endothelial activation (decreased sICAM-1 and vWF, and increased angiopoeitin-1 levels in peripheral blood) in an experimental cerebral malaria model. Mice that received inhaled nitric oxide starting prior to infection had reduced parasitized erythrocyte accumulation in the brain, decreased brain expression of ICAM-1, and preserved vascular integrity compared to control mice. Inhaled nitric oxide administered in combination with artesunate, starting as late as 5.5 days post-infection, improved survival over treatment with artesunate alone (70% survival in the artesunate only vs. 100% survival in the artesunate plus iNO group, pu200a=u200a0.03). These data support the clinical investigation of inhaled nitric oxide as a novel adjunctive therapy in patients with severe malaria.

HIV protease inhibitor use during pregnancy is associated with decreased progesterone levels, suggesting a potential mechanism contributing to fetal growth restriction.

BACKGROUNDnProtease inhibitor (PI)-based combination antiretroviral therapy (cART) is administered during pregnancy to prevent perinatal human immunodeficiency virus (HIV) transmission. However, PI use has been associated with adverse birth outcomes, including preterm delivery and small-for-gestational-age (SGA) births. The mechanisms underlying these outcomes are unknown. We hypothesized that PIs contribute to these adverse events by altering progesterone levels.nnnMETHODSnPI effects on trophoblast progesterone production were assessed in vitro. A mouse pregnancy model was used to assess the impact of PI-based cART on pregnancy outcomes and progesterone levels in vivo. Progesterone levels were assessed in plasma specimens from 27 HIV-infected and 17 HIV-uninfected pregnant women.nnnRESULTSnPIs (ritonavir, lopinavir, and atazanavir) but not nucleoside reverse transcriptase inhibitors (NRTIs) or nonnucleoside reverse transcriptase inhibitors reduced trophoblast progesterone production in vitro. In pregnant mice, PI-based cART but not dual-NRTI therapy was associated with significantly lower progesterone levels that directly correlated with fetal weight. Progesterone supplementation resulted in a significant improvement in fetal weight. We observed lower progesterone levels and smaller infants in HIV-infected women receiving PI-based cART, compared with the control group. In HIV-infected women, progesterone levels correlated significantly with birth weight percentile.nnnCONCLUSIONSnOur data suggest that PI use in pregnancy may lead to lower progesterone levels that could contribute to adverse birth outcomes.

Cerebral malaria: human versus mouse studies

In a recent Opinion article [1], White and colleagues discuss the value of the murine Plasmodium berghei ANKA model in identifying pathological processes and therapeutic interventions in human cerebral malaria (HCM). This model involves P. berghei ANKA infection of inbred CBA or C57BL/6 strain mice, which develop clinical symptoms of cerebral complications including paralysis, fitting and coma with death around Day 8 post-infection [2]. Resistant mouse strains such as BALB/c mice develop hyperparasitemia and severe anemia with death occurring about 3 weeks after infection.

PPARγ Agonists Improve Survival and Neurocognitive Outcomes in Experimental Cerebral Malaria and Induce Neuroprotective Pathways in Human Malaria

Cerebral malaria (CM) is associated with a high mortality rate, and long-term neurocognitive impairment in approximately one third of survivors. Adjunctive therapies that modify the pathophysiological processes involved in CM may improve outcome over anti-malarial therapy alone. PPARγ agonists have been reported to have immunomodulatory effects in a variety of disease models. Here we report that adjunctive therapy with PPARγ agonists improved survival and long-term neurocognitive outcomes in the Plasmodium berghei ANKA experimental model of CM. Compared to anti-malarial therapy alone, PPARγ adjunctive therapy administered to mice at the onset of CM signs, was associated with reduced endothelial activation, and enhanced expression of the anti-oxidant enzymes SOD-1 and catalase and the neurotrophic factors brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the brains of infected mice. Two months following infection, mice that were treated with anti-malarials alone demonstrated cognitive dysfunction, while mice that received PPARγ adjunctive therapy were completely protected from neurocognitive impairment and from PbA-infection induced brain atrophy. In humans with P. falciparum malaria, PPARγ therapy was associated with reduced endothelial activation and with induction of neuroprotective pathways, such as BDNF. These findings provide insight into mechanisms conferring improved survival and preventing neurocognitive injury in CM, and support the evaluation of PPARγ agonists in human CM.

The importance of motherhood in HIV-positive women of reproductive age in Ontario, Canada

Motherhood is personally, culturally, and historically rooted. Recent publications have focused on medical issues related to pregnancy and HIV, with attention on fetal well-being. There is limited literature on the importance of motherhood for HIV-positive women. Our studys purpose was to investigate the importance of motherhood among HIV-positive women of reproductive age in Ontario, Canada and to analyze the correlates thereof. We present our findings using a secondary analysis of cross-sectionally collected data from a study assessing fertility desires and intentions of HIV-positive women. The sub-analysiss outcome of interest was based on the question: “Being a mother is important to me” with a 5-point Likert scale that was dichotomized into strongly agree/agree vs. neutral/disagree/strongly disagree. Logistic regression models were fit to calculate unadjusted and adjusted odds ratios (ORs) for significant correlates. Of the 497 respondents, median age was 38 (interquartile range [IQR] 32–43), 46% were African, 74% had given birth, and 57% intended to give birth. A total of 452 (91%) agreed (N = 75) or strongly agreed (N = 377) that being a mother was important to them. Age less than 40 years (OR 3.0; 95% confidence interval [CI] 1.6–5.7, African ethnicity (OR 9.2; 95% CI 3.2–26.3), immigration within 10 years (OR 19.6, 95% CI 4.6–83.1), and partner or family desire for a pregnancy (OR 3.3; 95% CI 1.5–7.3) were significant correlates of the importance of motherhood in a univariate analysis. Importance of motherhood was associated with desire (OR 6.2, 95% CI 3.1–12.3) and intention to give birth (OR 6.9, 95% CI 3.1–15.2), and previous birth (OR 8.5, 95% CI 4.2–16.8). In the multivariable model, the significant correlates were of age less than 40 years (OR 3.9; 95% CI 1.8–8.4), immigration within 10 years (OR 14.1; 95% CI 3.2–61.5), and having previously given birth (OR 11.2; 95% CI 5.1–24.4). The majority of women felt strongly that motherhood was important to them particularly among younger women, recent immigrants, and women who were mothers.

CD47-SIRPα Interactions Regulate Macrophage Uptake of Plasmodium falciparum-Infected Erythrocytes and Clearance of Malaria In Vivo

ABSTRACT CD47 engagement by the macrophage signal regulatory protein alpha (SIRPα) inhibits phagocytic activity and protects red blood cells (RBCs) from erythrophagocytosis. The role of CD47-SIRPα in the innate immune response to Plasmodium falciparum infection is unknown. We hypothesized that disruption of SIRPα signaling may enhance macrophage uptake of malaria parasite-infected RBCs. To test this hypothesis, we examined in vivo clearance in CD47-deficient mice infected with Plasmodium berghei ANKA and in vitro phagocytosis of P. falciparum-infected RBCs by macrophages from SHP-1-deficient (Shp-1 −/− ) mice and NOD.NOR-Idd13.Prkdc scid (NS-Idd13) mice, as well as human macrophages, following disruption of CD47-SIRPα interactions with anti-SIRPα antibodies or recombinant SIRPα-Fc fusion protein. Compared to their wild-type counterparts, Cd47 −/− mice displayed significantly lower parasitemia, decreased endothelial activation, and enhanced survival. Using macrophages from SHP-1-deficient mice or from NS-Idd13 mice, which express a SIRPα variant that does not bind human CD47, we showed that altered SIRPα signaling resulted in enhanced phagocytosis of P. falciparum-infected RBCs. Moreover, disrupting CD47-SIRPα engagement using anti-SIRPα antibodies or SIRPα-Fc fusion protein also increased phagocytosis of P. falciparum-infected RBCs. These results indicate an important role for CD47-SIRPα interactions in innate control of malaria and suggest novel targets for intervention.

Optimizing Malaria Treatment in the Community

Over 200 million cases of malaria are reported annually to the WHO, including 627,000 deaths, mostly among children. These alarming figures persist although malaria is an entirely curable infection with currently available medications promptly deployed. Most malaria infections occur in resource-limited rural settings with poor access to medical care. Therefore, one of the primary challenges in optimizing antimalarial treatment is delivery of care to underserved communities. Alternative strategies to physician-guided, laboratory-assisted, diagnosis and treatment will be required in order to reach the large number of cases of uncomplicated malaria that arise in rural communities. The authors suggest that these challenges can be addressed with well-designed programs featuring training of community health workers, increased attention to supply management, and better community engagement. Models of integrated community case management, shown successful elsewhere, should be implemented in order to optimize antimalarial drug treatment for children in low-resource settings.