Tuan M. Tran

Estradiol enhances thiazide-sensitive NaCl cotransporter density in the apical plasma membrane of the distal convoluted tubule in ovariectomized rats.

Recent data suggest that sex hormones affect the thiazide-sensitive NaCl cotransporter (TSC) density or binding capacity (Chen, Z., D.A. Vaughn, and D.D. Fanestil. 1994. J. Am. Soc. Nephrol. 5:1112-1119). Thus, we determined the effect of ovariectomy (OVX) and estrogen replacement on the ultrastructural localization of TSC in rat kidney using immunocytochemistry. Kidneys of intact female (CON) and OVX rats fed ad libitum for 6 and 9 wk or pair-fed for 9 wk were processed for transmission electron microscopy. Immunogold localization of rat TSC (rTSC1) demonstrated intense label in the apical plasma membrane of CON distal convoluted tubule (DCT). In OVX DCT, rTSC1 label and apical plasma membrane microprojections were decreased. Western blots of renal membrane protein from pair-fed CON and OVX revealed bands at 129-135 kD, but the OVX signal was reduced. Morphometric analyses demonstrated that injecting 10 microg/ kg body weight 17beta-estradiol subcutaneously 4x/wk in OVX rats restored DCT apical microprojections and label density for rTSC1. Thus, in OVX rats (a) rTSC1 immunoreactive renal membrane protein is reduced; (b) apical plasma membrane complexity and immunogold label for rTSC1 in DCT is decreased; and (c) estradiol replacement restores DCT ultrastructure and rTSC1 label to normal. We conclude that estrogen enhances the density of rTSC1 in the DCT, and may alter renal Na transport by this mechanism.

Gut Microbiota Elicits a Protective Immune Response against Malaria Transmission

Summary Glycosylation processes are under high natural selection pressure, presumably because these can modulate resistance to infection. Here, we asked whether inactivation of the UDP-galactose:β-galactoside-α1-3-galactosyltransferase (α1,3GT) gene, which ablated the expression of the Galα1-3Galβ1-4GlcNAc-R (α-gal) glycan and allowed for the production of anti-α-gal antibodies (Abs) in humans, confers protection against Plasmodium spp. infection, the causative agent of malaria and a major driving force in human evolution. We demonstrate that both Plasmodium spp. and the human gut pathobiont E. coli O86:B7 express α-gal and that anti-α-gal Abs are associated with protection against malaria transmission in humans as well as in α1,3GT-deficient mice, which produce protective anti-α-gal Abs when colonized by E. coli O86:B7. Anti-α-gal Abs target Plasmodium sporozoites for complement-mediated cytotoxicity in the skin, immediately after inoculation by Anopheles mosquitoes. Vaccination against α-gal confers sterile protection against malaria in mice, suggesting that a similar approach may reduce malaria transmission in humans. PaperFlick

An Intensive Longitudinal Cohort Study of Malian Children and Adults Reveals No Evidence of Acquired Immunity to Plasmodium falciparum Infection

BACKGROUND In experimental models of human and mouse malaria, sterilizing liver stage immunity that blocks progression of Plasmodium infection to the symptomatic blood stage can be readily demonstrated. However, it remains unclear whether individuals in malaria-endemic areas acquire such immunity. METHODS In Mali, 251 healthy children and adults aged 4-25 years who were free of blood-stage Plasmodium infection by polymerase chain reaction (PCR) were enrolled in a longitudinal study just prior to an intense 6-month malaria season. Subsequent clinical malaria episodes were detected by weekly active surveillance and self-referral. Asymptomatic P. falciparum infections were detected by blood-smear microscopy and PCR analysis of dried blood spots that had been collected every 2 weeks for 7 months. RESULTS As expected, the risk of clinical malaria decreased with increasing age (log-rank test, P = .0038). However, analysis of PCR data showed no age-related differences in P. falciparum infection risk (log-rank test, P = .37). CONCLUSIONS Despite years of exposure to intense P. falciparum transmission, there is no evidence of acquired, sterile immunity to P. falciparum infection in this population, even as clinical immunity to blood-stage malaria is clearly acquired. Understanding why repeated P. falciparum infections do not induce sterile protection may lead to insights for developing vaccines that target the liver stage in malaria-endemic populations.

Naturally Acquired Antibodies Specific for Plasmodium falciparum Reticulocyte-Binding Protein Homologue 5 Inhibit Parasite Growth and Predict Protection From Malaria

BACKGROUND Plasmodium falciparum reticulocyte-binding protein homologue 5 (PfRH5) is a blood-stage parasite protein essential for host erythrocyte invasion. PfRH5-specific antibodies raised in animals inhibit parasite growth in vitro, but the relevance of naturally acquired PfRH5-specific antibodies in humans is unclear. METHODS We assessed pre-malaria season PfRH5-specific immunoglobulin G (IgG) levels in 357 Malian children and adults who were uninfected with Plasmodium. Subsequent P. falciparum infections were detected by polymerase chain reaction every 2 weeks and malaria episodes by weekly physical examination and self-referral for 7 months. The primary outcome was time between the first P. falciparum infection and the first febrile malaria episode. PfRH5-specific IgG was assayed for parasite growth-inhibitory activity. RESULTS The presence of PfRH5-specific IgG at enrollment was associated with a longer time between the first blood-stage infection and the first malaria episode (PfRH5-seropositive median: 71 days, PfRH5-seronegative median: 18 days; P = .001). This association remained significant after adjustment for age and other factors associated with malaria risk/exposure (hazard ratio, .62; P = .02). Concentrated PfRH5-specific IgG purified from Malians inhibited P. falciparum growth in vitro. CONCLUSIONS Naturally acquired PfRH5-specific IgG inhibits parasite growth in vitro and predicts protection from malaria. These findings strongly support efforts to develop PfRH5 as an urgently needed blood-stage malaria vaccine. CLINICAL TRIALS REGISTRATION NCT01322581.

Circulating Th1-Cell-type Tfh Cells that Exhibit Impaired B Cell Help Are Preferentially Activated during Acute Malaria in Children.

Malaria-specific antibody responses are short lived in children, leaving them susceptible to repeated bouts of febrile malaria. The cellular and molecular mechanisms underlying this apparent immune deficiency are poorly understood. Recently, T follicular helper (Tfh) cells have been shown to play a critical role in generating long-lived antibody responses. We show that Malian children have resting PD-1(+)CXCR5(+)CD4(+) Tfh cells in circulation that resemble germinal center Tfh cells phenotypically and functionally. Within this population, PD-1(+)CXCR5(+)CXCR3(-) Tfh cells are superior to Th1-polarized PD-1(+)CXCR5(+)CXCR3(+) Tfh cells in helping B cells. Longitudinally, we observed that malaria drives Th1 cytokine responses, and accordingly, the less-functional Th1-polarized Tfh subset was preferentially activated and its activation did not correlate with antibody responses. These data provide insights into the Tfh cell biology underlying suboptimal antibody responses to malaria in children and suggest that vaccine strategies that promote CXCR3(-) Tfh cell responses may improve malaria vaccine efficacy.

Psychosis with paranoid delusions after a therapeutic dose of mefloquine: a case report

BackgroundConvenient once-a-week dosing has made mefloquine a popular choice as malaria prophylaxis for travel to countries with chloroquine-resistant malaria. However, the increased use of mefloquine over the past decade has resulted in reports of rare, but severe, neuropsychiatric adverse reactions, such as anxiety, depression, hallucinations and psychosis. A direct causality between mefloquine and severe reactions among travelers has been partly confounded by factors associated with foreign travel and, in the case of therapeutic doses of mefloquine, the central nervous system manifestations of Plasmodium infection itself. The present case provides a unique natural history of mefloquine-induced neuropsychiatric toxicity and revisits its dose-dependent nature.Case presentationThis report describes an acute exacerbation of neuropsychiatric symptoms after an unwarranted therapeutic dose (1250 mg) of mefloquine in a 37-year-old male previously on a once-a-week prophylactic regimen. Neuropsychiatric symptoms began as dizziness and insomnia of several days duration, which was followed by one week of escalating anxiety and subtle alterations in behaviour. The patients anxiety culminated into a panic episode with profound sympathetic activation. One week later, he was hospitalized after developing frank psychosis with psychomotor agitation and paranoid delusions. His psychosis remitted with low-dose quetiapine.ConclusionThis report suggests that an overt mefloquine-induced psychosis can be preceded by a prodromal phase of moderate symptoms such as dizziness, insomnia, and generalized anxiety. It is important that physicians advise patients taking mefloquine prophylaxis and their relatives to recognize such symptoms, especially when they are accompanied by abrupt, but subtle, changes in behaviour. Patients with a history of psychiatric illness, however minor, may be at increased risk for a mefloquine-induced neuropsychiatric toxicity. Physicians must explicitly caution patients not to self-medicate with a therapeutic course of mefloquine when a malaria diagnosis has not been confirmed.

Naturally acquired humoral and cellular immune responses to Plasmodium vivax merozoite surface protein 9 in Northwestern Amazon individuals

Antibody and T-cell reactivities to Plasmodium vivax merozoite surface protein 9 (PvMSP9) were evaluated in a cross-sectional study of individuals naturally exposed to malaria infections living in Ribeirinha, a native riverine community and in Colina, a transmigrant community, Rondonia, Brazil. The antibody responses to PvMSP9-RIRIIand PvMSP9-Nt domains in Ribeirinha were higher compared with Colina and correlated with age and time of malaria exposure. IgG2 was most prevalent for PvMSP9-RII in both communities, and IgG1 was the predominant isotype for PvMSP9-Nt and PvMSP9-RIRII in Ribeirinha. IFN-gamma and IL-4 predominated in Ribeirinha, while IFN-gamma predominated in Colina. Variation in exposure to P. vivax likely accounts for the differences observed in cytokine and antibody levels between the two populations studied.

Detection of a Plasmodium vivax erythrocyte binding protein by flow cytometry

The malaria parasite Plasmodium vivax preferentially invades reticulocytes. It is therefore relevant for vaccine development purposes to identify and characterize P. vivax proteins that bind specifically to the surface of reticulocytes. We have developed a two‐color flow cytometric erythrocyte binding assay (F‐EBA) that has several advantages over traditional erythrocyte binding assays (T‐EBAs) used in malaria research. We demonstrate the use of F‐EBA using the P. vivax Duffy binding protein region II (PvDBP‐RII) recombinant protein as a model. This protein binds to all erythrocytes that express the Duffy receptor (Fy) and discriminates binding between normocytes and reticulocytes.

Targeting glutamine metabolism rescues mice from late-stage cerebral malaria

Significance Cerebral malaria (CM) is a deadly complication of Plasmodium falciparum infection in African children despite effective antimalarial treatment. Once signs of neurologic disease have commenced, there is no adjunctive treatment for CM, and overall mortality remains high. Thus, a treatment that arrests disease and promotes healing in the late stages is urgently needed. Here we report, in an animal model of CM, that the glutamine analog 6-diazo-5-oxo-L-norleucine (DON) is an effective therapy even when treatment is initiated after infected animals show neurological signs of disease. Within hours of DON treatment blood–brain barrier integrity was restored, and brain swelling was reduced. These results suggest DON as a strong candidate for an effective adjunctive therapy for CM in African children. The most deadly complication of Plasmodium falciparum infection is cerebral malaria (CM) with a case fatality rate of 15–25% in African children despite effective antimalarial chemotherapy. There are no adjunctive treatments for CM, so there is an urgent need to identify new targets for therapy. Here we show that the glutamine analog 6-diazo-5-oxo-l-norleucine (DON) rescues mice from CM when administered late in the infection a time at which mice already are suffering blood–brain barrier dysfunction, brain swelling, and hemorrhaging accompanied by accumulation of parasite-specific CD8+ effector T cells and infected red blood cells in the brain. Remarkably, within hours of DON treatment mice showed blood–brain barrier integrity, reduced brain swelling, decreased function of activated effector CD8+ T cells in the brain, and levels of brain metabolites that resembled those in uninfected mice. These results suggest DON as a strong candidate for an effective adjunctive therapy for CM in African children.

Stool microbiota composition is associated with the prospective risk of Plasmodium falciparum infection.

BackgroundIn humans it is unknown if the composition of the gut microbiota alters the risk of Plasmodium falciparum infection or the risk of developing febrile malaria once P. falciparum infection is established. Here we collected stool samples from a cohort composed of 195 Malian children and adults just prior to an intense P. falciparum transmission season. We assayed these samples using massively parallel sequencing of the 16S ribosomal RNA gene to identify the composition of the gut bacterial communities in these individuals. During the ensuing 6-month P. falciparum transmission season we examined the relationship between the stool microbiota composition of individuals in this cohort and their prospective risk of both P. falciparum infection and febrile malaria.ResultsConsistent with prior studies, stool microbial diversity in the present cohort increased with age, although the overall microbiota profile was distinct from cohorts in other regions of Africa, Asia and North America. Age-adjusted Cox regression analysis revealed a significant association between microbiota composition and the prospective risk of P. falciparum infection; however, no relationship was observed between microbiota composition and the risk of developing febrile malaria once P. falciparum infection was established.ConclusionsThese findings underscore the diversity of gut microbiota across geographic regions, and suggest that strategic modulation of gut microbiota composition could decrease the risk of P. falciparum infection in malaria-endemic areas, potentially as an adjunct to partially effective malaria vaccines.