Plasmodium vivax (P. vivax) can lead to severe hematological complications, including anemia and thrombocytopenia, which may require hospitalization. This prospective observational study investigated the adaptive immune response in pediatric P. vivax malaria, focusing on sustained IFN-γ production in CD4+ and CD8+ memory T cells as markers of immune protection. Conducted at the Dr. Heitor Vieira Dourado Tropical Medicine Foundation (FMT-HVD) in the Western Brazilian Amazon, peripheral blood mononuclear cells (PBMCs) were collected from 25 children aged 1-16 years at diagnosis (D0, acute phase) and 90 days post-treatment (D90, convalescent phase). PBMCs were stimulated ex vivo with the conserved P. vivax antigen, the 19 kDa fragment of the C-terminal region of merozoite surface protein-1 (PvMSP119), and intracellular production of IFN-γ was quantified in memory T cells (CD3+CD4+CD45RO+ and CD3+CD8+CD45RO+ T cells) by flow cytometry. Individuals whose cells specifically produced IFN-γ against PvMSP119 on both D0 and D90 were classified as responders, while those who responded in only one phase or in neither were classified as nonresponders. Responders, whose CD3+CD4+CD45RO+ T cells exhibited sustained IFN-γ response against PvMSP119 demonstrated lower parasite density as well as improved normalization of hemoglobin levels and recovery of platelet counts. These results confirm the role of this response as acquisition of immunity. PvMSP119 antigen emerges as a promising marker of sustained immunity, though larger studies are required to evaluate its long-term impact on recovery and outcomes. These findings underscore the critical role of IFN-γ-producing memory T cells in controlling parasitemia and mitigating anemia and thrombocytopenia in pediatric P. vivax malaria.

We hypothesized that variants in inflammasome-related genes could influence susceptibility to gestational malaria (GM). To test this, we conducted an association study in a cohort of pregnant women from a malaria-endemic region in northern Brazil, assessing whether specific functional single nucleotide variants (SNVs) in inflammasome genes affect (1) the response to Plasmodium infection and (2) the development of placental malaria. Our findings revealed that the NLRP1 p.Met1154Val variant was associated with a protective effect against Plasmodium infection. Moreover, IL1B SNVs appeared more prevalent in severe cases. Additionally, multivariate analyses incorporating placental blood cytokines, growth factors, and immunohistochemical features revealed that the NLRP1 p.Met1154Val variant correlated with a healthier placental state, highlighting a potential protective role of the NLRP1 inflammasome in GM. For the first time, we showed that infected red blood cells induce NLRP1- and caspase-1-dependent pyroptosis in BeWo trophoblast cells, identifying a novel inflammasome pathway involved in GM pathogenesis. Our study identifies a genetic variant underlying NLRP1 contribution to GM and suggests that NLRP1 may be an under-explored inflammasome receptor in malaria and infected erythrocytes' sensing. © 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Alterations in angiogenic proteins play a role in newborn growth potential, and they have been widely studied, but not further explored in malaria research. We aimed to identify maternal peripheral proteins that are associated with newborn growth parameters in the context of malaria in pregnancy. We analysed data and biological samples collected from 386 pregnant women with and without malaria selected from previous cohort study in the Amazon region, Brazil, between 2013 and 2015. ELISAs were used to quantify Ang-1, Ang-2, Tie2, VEGF, sFlt1, VEGFR2, PlGF, sENG, and leptin in peripheral plasma at time of delivery. We generated receiver operating characteristic curves and multivariable logistic regression models to assess the associations of maternal peripheral protein levels with the anthropometric profiles of newborns. Tie2, sFlt1, sENG and leptin were associated to growth parameters in newborns of mothers who had malaria during pregnancy. sFlt1 levels were associated with newborn weight and length, and sENG was associated with newborn length in Plasmodium vivax-infected women. Tie2, sFlt1 and leptin levels were associated with newborn length in Plasmodium falciparum-infected women. Identifying maternal peripheral proteins associated with newborn outcomes might help in understanding biological dynamics of malaria in pregnancy in areas of low transmission, improving future health interventions, and encourage further studies with angiogenic proteins.

Epigenetic regulation plays a central role in the developmental control and antigenic variation of Plasmodium falciparum , yet the functions of many chromatin-modifying enzymes remain poorly understood. Here, we investigated the role of the putative Jumonji C (JmjC) domain–containing enzyme PfJmjC2 (PF3D7_0602800) in maintaining chromatin organization and histone modification balance during the asexual blood stages of the parasite. Using a conditional glmS ribozyme-mediated knockdown system, we achieved a ∼70% reduction in PfJmjC2 transcript and protein levels, which resulted in a marked delay in DNA replication and intraerythrocytic development. Immunoprecipitation assays revealed that PfJmjC2 physically interacts with histone H2A, suggesting an association with the nucleosome core. Upon PfJmjC2 depletion, the balance of epigenetic marks was disrupted, indicating a shift toward a more compact and transcriptionally repressed chromatin state. MNase–ChIP–PCR analysis further showed that PfJmjC2 associates with nucleosome-dense regions, including var gene promoters, although its reduction did not alter var gene transcription or switching patterns. Together, these findings indicate that PfJmjC2 contributes to chromatin organization and nucleosome stability rather than direct transcriptional control, highlighting its potential role in maintaining chromatin compaction and epigenetic homeostasis in P. falciparum . ### Competing Interest Statement The authors have declared no competing interest. FAPESP, 2015/17174-7, 2017/24267-7 and 2021/13727-2

Post-translational protein modifications (PTMs) significantly enhance the functional diversity of proteins and are therefore important for the expansion and the dynamics of the cell’s proteome. In addition to structurally simpler PTMs, substrates also undergo modification through the reversible attachment of small proteins. The best understood PTM of this nature to date is the covalent conjugation of ubiquitin and ubiquitin-like proteins (UBLs) to their substrates. The protein family of small ubiquitin-like modifier (SUMO) is one of these UBLs that has received increasing scientific attention. The pathway of SUMOylation is highly conserved in all eukaryotic cells and is crucial for their survival. It plays an essential role in many biological processes, such as the maintenance of genomic integrity, transcriptional regulation, gene expression, and the regulation of intracellular signal transduction, and thereby influences DNA damage repair, immune responses, cell cycle progression, and apoptosis. Several studies have already shown that in this context protein SUMOylation is involved in the control mechanisms of various cellular receptors. This article unites data from different studies focusing on the investigation of the strictly conserved three-step enzyme cascade of protein SUMOylation and the functional analysis of the involved proteins E1, E2, and E3 and SUMOylation target proteins. Furthermore, this review highlights the role of nuclear receptor SUMOylation and its importance for the cellular functionality and disease development arising from defects in correct protein SUMOylation.

An optimization of the pyridylpiperazine series against Plasmodium falciparum has been performed, exploring a structure-activity relationship carried out on the toluyl fragment of hit 1, a compound with low micromolar activity against Plasmodium falciparum discovered by high-throughput screening. After confirming the crucial role played by this aryl fragment in the antiplasmodial activity, the replacement of the ortho-methyl substituent of 1 by halogenated ones led to an improvement for four analogs, either in terms of potency, expected pharmacokinetics profile, or both. Further introduction of endocyclic nitrogens in this fragment identified two more optimized compounds, 20 and 23, which are expected to be much more metabolically stable than 1. Additional assessment of the cytotoxicity, Ligand Lipophilic Efficiency, potency against the chloroquine-resistant Dd2 strain and in silico ADMET predictions revealed a satisfactory profile for most compounds, ultimately identifying the four optimized compounds 7, 9, 20 and 23 as promising compounds for further lead optimization of this series against Plasmodium falciparum.

Background Plasmodium vivax infection, when it occurs during pregnancy, has often been associated with serious adverse pregnancy outcomes. However, immunological alterations in pregnancy and their consequences have been little explored. We characterized the humoral immune response in pregnant women exposed to malaria by P. vivax antigens and its association with the maternal inflammatory profile and poor pregnancy outcomes. Methods An observational cohort study in the Brazilian Amazon was conducted between 2013 and 2015. After applying exclusion criteria, 242 mother-child pairs were included in the analysis. Data on maternal infection, gestational outcomes, and inflammatory factors were evaluated in the maternal peripheral plasma. In samples from the first infection, the presence of total IgG and its subclasses in plasma against PvMSP119 protein were also quantified. Results Previous exposure to malaria, observed by anti-total IgG antibodies to the PvMSP119 antigen, increased the inflammatory response to infection when the pregnant woman had malaria during pregnancy. IL-6 and IL-10 levels were positively correlated with parasitemia and with total IgG levels; but they were negatively correlated with the gestational age at delivery from Pv-infected woman. In multivariate linear regression analyses, IgG 1, 2 and 4 was negatively and positively associated with cytokines IL-6 and IL-10, respectively, in P. vivax-infection. Conclusions An association between the humoral immune response and the peripheral inflammatory cytokine profile with the adverse outcomes in malaria in pregnancy by P. vivax was observed. Previous exposure to the parasite can influence the IL-6 and IL-10 response, which is associated with increased parasitemia, reduced maternal weight gain and premature delivery.

Background: Nucleic acid-based vaccines have been studied for the past four decades, but the approval of the first messenger RNA (mRNA) vaccines during the COVID-19 pandemic opened renewed perspectives for the development of similar vaccines against different infectious diseases. Presently available mRNA vaccines are based on non-replicative mRNA, which contains modified nucleosides encased in lipid vesicles, allowing for entry into the host cell cytoplasm, and reducing inflammatory reactions. An alternative immunization strategy employs self-amplifying mRNA (samRNA) derived from alphaviruses, but lacks viral structural genes. Once incorporated into ionizable lipid shells, these vaccines lead to enhanced gene expression, and lower mRNA doses are required to induce protective immune responses. In the present study, we tested a samRNA vaccine formulation based on the SP6 Venezuelan equine encephalitis (VEE) vector incorporated into cationic liposomes (dimethyldioctadecyl ammonium bromide and a cholesterol derivative). Three vaccines were generated that encoded two reporter genes (GFP and nanoLuc) and the Plasmodium falciparum reticulocyte binding protein homologue 5 (PfRH5). Methods: Transfection assays were performed using Vero and HEK293T cells, and the mice were immunized via the intradermal route using a tattooing device. Results: The liposome–replicon complexes showed high transfection efficiencies with in vitro cultured cells, whereas tattooing immunization with GFP-encoding replicons demonstrated gene expression in mouse skin up to 48 h after immunization. Mice immunized with liposomal PfRH5-encoding RNA replicons elicited antibodies that recognized the native protein expressed in P. falciparum schizont extracts, and inhibited the growth of the parasite in vitro. Conclusion: Intradermal delivery of cationic lipid-encapsulated samRNA constructs is a feasible approach for developing future malaria vaccines.

Conditional gene expression is a powerful tool to investigate putative vaccine and drug targets, especially in a haploid organism such as Plasmodium falciparum. Inducible systems based on regulation of either transcription, translation, protein or mRNA stability, among others, allow switching on an off the expression of any desired gene causing specific gain or loss of function phenotypes. However, those systems can be cumbersome involving the construction of large plasmids and generation of multiple transgenic parasite lines. In addition, the dynamic range of regulation achieved is not predictable for each individual gene and can be insufficient to generate detectable phenotypes when the genes of interest are silenced. Here, we combined up to three distinct inducible systems to regulate the expression of a single gene. Expression of the reporter NanoLuc luciferase was regulated over 40-fold, which correlates to the regulation achieved by each individual system multiplied by each other. We applied the conditionally expressed NanoLuc to evaluate the effect of fast-acting antimalarials such as chloroquine and artesunate as well as of slower-acting ones such as atovaquone. The conditionally expressed reporter allowed faster and more reliable detection of toxicity to the parasite, which correlated to the expected action of each compound. Bioluminescence achieved by the expression of this inducible highly sensitive reporter is therefore a promising tool to investigate the temporal effect of potential new antimalarials. This single plasmid combination system might also prove useful to achieve sufficient regulation of genes of interest to produce loss-of-function phenotypes.

The complex life cycle of the malaria parasite Plasmodium requires the parasite to adequately adapt to different conditions. For this reason, Plasmodium strictly controls its gene expression, and given its evolutionary distance from the human host, the involved factors may figure as attractive potential drug targets. In recent years, several unique transcription factors and chromatin modifiers have been identified and partially characterized in Plasmodium falciparum and in the murine species P. yoelii and P. berghei. This review unites data from studies focusing on drug development against enigmatic plant-like AP2-transcription factors and chromatin modifiers, such as histone acetyl transferases and deacetylases and histone methyltransferases and demethylases. Considering the reported success of inhibition of both factors, these may be included as targets to effectively combat the parasite by perturbing its control of gene expression.

Background Pregnant women have increased susceptibility to Plasmodium falciparum malaria and acquire protective antibodies over successive pregnancies. Most studies that investigated malaria antibody responses in pregnant women are from high transmission areas in sub-Saharan Africa, while reports from Latin America are scarce and inconsistent. The present study sought to explore the development of antibodies against P. falciparum and Plasmodium vivax antigens in pregnant women living in a low transmission area in the Brazilian Amazon. Methods In a prospective cohort study, plasma samples from 408 pregnant women (of whom 111 were infected with P. falciparum , 96 had infections with P. falciparum and P. vivax , and 201 had no Plasmodium infection) were used to measure antibody levels. Levels of IgG and opsonizing antibody to pregnancy-specific variant surface antigens (VSAs) on infected erythrocytes (IEs), 10 recombinant VAR2CSA Duffy binding like (DBL domains), 10 non-pregnancy-specific P. falciparum merozoite antigens, and 10 P. vivax antigens were measured by flow cytometry, ELISA, and multiplex assays. Antibody levels and seropositivity among the groups were compared. Results Antibodies to VSAs on P. falciparum IEs were generally low but were higher in currently infected women and women with multiple P. falciparum episodes over pregnancy. Many women (21%-69%) had antibodies against each individual VAR2CSA DBL domain, and antibodies to DBLs correlated with each other (r ≥ 0.55, p < 0.0001), but not with antibody to VSA or history of infection. Infection with either malaria species was associated with higher seropositivity rate for antibodies against P. vivax proteins, adjusted odds ratios (95% CI) ranged from 5.6 (3.2, 9.7), p < 0.0001 for PVDBPII-Sal1 to 15.7 (8.3, 29.7), p < 0.0001 for PvTRAg_2. Conclusions Pregnant Brazilian women had low levels of antibodies to pregnancy-specific VSAs that increased with exposure. They frequently recognized both VAR2CSA DBL domains and P. vivax antigens, but only the latter varied with infection. Apparent antibody prevalence is highly dependent on the assay platform used.

Apicomplexan parasites have a significant impact on human and livestock health. The most important apicomplexan parasite is Plasmodium, the pathogenic agent of malaria. Malaria is a devastating and quite often deadly parasitic disease that causes substantial public health problems in tropical regions. Due to the high mutational rate of apicomplexan pathogens and their resulting rapid adaptation to environmental changes, or inadequate treatment, drug resistance to the standard and conventional medication is increasing. Therefore, continuous discovery of novel drug targets and the development of new chemotherapeutic agents are essential. In this Research Topic “From Apicomplexan Genes to Drug Discovery” we were focussing primary on malaria drug discovery. Several authors have contributed papers to this Research Topic, and an overview of the scientific content is summarized below. van Heerden et al. demonstrated in their original article machine learning (ML) algorithms to predict the possible mode of action (MoA) of novel compounds. The early identification of the MoA can accelerate hit prioritization, hit-to-lead optimization, and preclinical combination studies in malaria research. Therefore, the authors applied ML on chemically-induced transcriptional profile to identify biochemical pathways on which a compound interferes and thereby signposts a possible interaction partner and the MoA. They assessed different ML approaches and found that only about 50 biomarkers were required to stratify compounds with similar MoA and define chemotranscriptomic fingerprints for each compound. Appropriate ML tools will facilitate the discovery of new drug targets and will support rapid identification of the MoA and of the novel not yet characterized compounds in the future. As commented in the review article on antimalarial drug discovery approaches by Rangel and Llinás in this special issue, chemotherapeutics are a major tool to cope with apicomplexan diseases; however, drug resistance against almost all antimalarials have been observed so far, which also includes the artemisinin-based combination therapies. New strategies to discover novel drugs and ideally irresistible drug targets and drug treatments to prevent the rapid formation of resistance in apicomplexan parasites in the near future are urgently needed and are the objective of this Research Topic. One novel druggable target is proposed by Sumam de Oliveira et al. They highlight targeting posttranslational modifications (PTMs) in order to interfere with the control of cellular activities.

The malaria parasite Plasmodium falciparum possesses a unique Acetyl-CoA Synthetase (PfACS) which provides acetyl moieties for different metabolic and regulatory cellular pathways. We characterized PfACS and studied its role focusing on epigenetic modifications using the var gene family as reporter genes. For this, mutant lines to modulate plasmodial ACS expression by degron-mediated protein degradation or ribozyme induced transcript decay were created. Additionally, an ACS inhibitor was tested for its effectiveness and specificity in interfering with Pf ACS. The knockdown of Pf ACS or its inhibition led to impaired parasite growth. Decreased levels of Pf ACS also led to differential histone acetylation patterns, altered variant gene expression and concomitantly decreased cytoadherence of infected red blood cells containing knocked-down parasites. Further, ChIP analysis revealed the presence of PfACS in many loci in ring stage parasites, underscoring its involvement in the regulation of chromatin. Due to its significant differences to human ACS, Pf ACS seems an interesting target for drug development.

Chikungunya virus (CHIKV) is responsible for a self-limited illness that can evolve into long-lasting painful joint inflammation. In this study, we report a novel experimental CHIKV vaccine formulation of lipid nanoparticles loaded with a recombinant protein derived from the E2 structural protein. This antigen fragment, designated ∆E2.1, maintained the antigenicity of the native viral protein and was specifically recognized by antibodies induced in CHIKV-infected patients. The antigen has been formulated into nanoparticles consisting of nano-multilamellar vesicles (NMVs) combined with the adjuvant monophosphoryl lipid A (MPLA). The vaccine formulation demonstrated a depot effect, leading to controlled antigen release, and induced strong antibody responses significantly higher than in mice immunized with the purified protein combined with the adjuvant. More relevantly, E2-specific antibodies raised in mice immunized with ∆E2.1-loaded NMV-MPLA neutralized CHIKV under in vitro conditions. Taken together, the results demonstrated that the new nanoparticle-based vaccine formulation represents a promising approach for the development of effective anti-CHIKV vaccines.

BACKGROUND:Malaria in Brazil represents one of the highest percentages of Latin America cases, where approximately 84% of infections are attributed to Plasmodium (P.) vivax. Despite the high incidence, many aspects of gestational malaria resulting from P. vivax infections remain poorly studied. As such, we aimed to evaluate the consequences of P. vivax infections during gestation on the health of mothers and their neonates in an endemic area of the Amazon. METHODS AND FINDINGS:We have conducted an observational cohort study in Brazilian Amazon between January 2013 and April 2015. 600 pregnant women were enrolled and followed until delivery. After applying exclusion criteria, 329 mother-child pairs were included in the analysis. Clinical data regarding maternal infection, newborn's anthropometric measures, placental histopathological characteristics, and angiogenic and inflammatory factors were evaluated. The presence of plasma IgG against the P. vivax (Pv) MSP119 protein was used as marker of exposure and possible associations with pregnancy outcomes were analyzed. Multivariate logistic regression analysis revealed that P. vivax infections during the first trimester of pregnancy are associated with adverse gestational outcomes such as premature birth (adjusted odds ratio [aOR] 8.12, 95% confidence interval [95%CI] 2.69-24.54, p < 0.0001) and reduced head circumference (aOR 3.58, 95%CI 1.29-9.97, p = 0.01). Histopathology analysis showed marked differences between placentas from P. vivax-infected and non-infected pregnant women, especially regarding placental monocytes infiltrate. Placental levels of vasomodulatory factors such as angiopoietin-2 (ANG-2) and complement proteins such as C5a were also altered at delivery. Plasma levels of anti-PvMSP119 IgG in infected pregnant women were shown to be a reliable exposure marker; yet, with no association with improved pregnancy outcomes. CONCLUSIONS:This study indicates that P. vivax malaria during the first trimester of pregnancy represents a higher likelihood of subsequent poor pregnancy outcomes associated with marked placental histologic modification and angiogenic/inflammatory imbalance. Additionally, our findings support the idea that antibodies against PvMSP119 are not protective against poor pregnancy outcomes induced by P. vivax infections.

Plasmodium malariae has a wide geographic distribution, but mainly at very low parasitemias and in co-infections, leading to an underestimated prevalence of this species. Studies for the detection of antibodies against Plasmodium recombinant proteins are increasingly used to map geographical distributions, seroprevalence and transmission intensities of malaria infection. However, no seroepidemiological survey using recombinant P. malariae proteins has been conducted in Brazil. This work evaluated the antibody response in serum samples of individuals from endemic regions of Brazil (the Amazon region and Atlantic Forest) against five recombinant proteins of P. malariae merozoite surface protein 1 (MSP1), and the MSP1 C-terminal portions of P. vivax and P. falciparum, in a multiplex assay. The positivity was 69.5% of samples recognizing at least one MSP1 recombinant protein. The mean of the Reactivity Index for the C-terminal portion of the P. falciparum was significantly higher compared to the other recombinant proteins, followed by the C-terminal of P. vivax and the N-terminal of P. malariae. Among the recombinant P. malariae proteins, the N-terminal of P. malariae showed the highest Reactivity Index alone. This study validates the use of the multiplex assay to measure naturally acquired IgG antibodies against Plasmodium MSP1 proteins and demonstrate that these proteins are important tools for seroepidemiological surveys and could be used in malaria surveillance.

Background Molecular and genetic studies of blood-stage Plasmodium falciparum parasites require limiting dilution cloning and prolonged cultivation in microplates. The entire process is laborious and subject to errors due to inaccurate dilutions at the onset and failed detection of parasite growth in individual microplate wells. Methods To precisely control the number of parasites dispensed into each microplate well, parasitaemia and total cell counts were determined by flow cytometry using parasite cultures stained with ethidium bromide or SYBR Green I. Microplates were seeded with 0.2 or 0.3 infected cells/well and cultivated with fresh erythrocytes. The c-SNARF fluorescent pH indicator was then used to reliably detect parasite growth. Results Flow cytometry required less time than the traditional approach of estimating parasitaemia and cell numbers by microscopic examination. The resulting dilutions matched predictions from Poisson distribution calculations and yielded clonal lines. Addition of c-SNARF to media permitted rapid detection of parasite growth in microplate wells with high confidence. Conclusion The combined use of flow cytometry for precise dilution and the c-SNARF method for detection of growth improves limiting dilution cloning of P. falciparum . This simple approach saves time, is scalable, and maximizes identification of desired parasite clones. It will facilitate DNA transfection studies and isolation of parasite clones from ex vivo blood samples.

The human malaria parasite Plasmodium falciparum expresses variant PfEMP1 proteins on the infected erythrocyte, which function as ligands for endothelial receptors in capillary vessels, leading to erythrocyte sequestration and severe malaria. The factors that orchestrate the mono-allelic expression of the 45–90 PfEMP1-encoding var genes within each parasite genome are still not fully identified. Here, we show that the transcription factor PfAP2-O influences the transcription of var genes. The temporary knockdown of PfAP2-O leads to a complete loss of var transcriptional memory and a decrease in cytoadherence in CD36 adherent parasites. AP2-O-knocked-down parasites exhibited also significant reductions in transmission through Anopheles mosquitoes. We propose that PfAP2-O is, beside its role in transmission stages, also one of the virulence gene transcriptional regulators and may therefore be exploited as an important target to disrupt severe malaria and block parasite transmission.

Placental malaria (PM) is associated with severe inflammation leading to abortion, preterm delivery, and intrauterine growth restriction. Innate immunity responses play critical roles, but the mechanisms underlying placental immunopathology are still unclear. Here, we investigated the role of inflammasome activation in PM by scrutinizing human placenta samples from an endemic area and ablating inflammasome components in a PM mouse model. The reduction in birth weight in babies from infected mothers is paralleled by increased placental expression of AIM2 and NLRP3 inflammasomes. Using genetic dissection, we reveal that inflammasome activation pathways are involved in the production and detrimental action of interleukin-1β (IL-1β) in the infected placenta. The IL-1R pharmacological antagonist Anakinra improved pregnancy outcomes by restoring fetal growth and reducing resorption in an experimental model. These findings unveil that IL-1β-mediated signaling is a determinant of PM pathogenesis, suggesting that IL-1R antagonists can improve clinical outcomes of malaria infection in pregnancy.