Biology subjects

Sinnis, P.

Publications and source records attributed to Sinnis, P..

At least 19 recordsLinked to original sources

bioRxiv2026

Identification of UCB-9721 as a potent inhibitor of MyoA, the essential class XIV myosin motor of apicomplexan parasites

The virulence of Toxoplasma gondii and other apicomplexan parasites relies on a unique form of cellular motility driven by MyoA, an unconventional class XIV myosin motor protein. To identify new chemical probes for investigating the molecular mechanisms of parasite motility, we screened over 50,000 small molecules for inhibitors of T. gondii MyoA (TgMyoA). The top hit from the screen, UCB-9721, is almost 40-fold more potent as an inhibitor of TgMyoA actin-activated ATPase activity than the previously described TgMyoA inhibitor, KNX-002, and 45-fold more potent at inhibiting parasite motility, with no detectable toxicity towards mammalian cells. UCB-9721 also inhibited the motility and/or growth of the related apicomplexan parasites Plasmodium falciparum, Cryptosporidium parvum, and Babesia duncani, suggesting that this compound will be a useful new chemical probe for studying motility and MyoA function in apicomplexan parasites more broadly. While UCB-9721 and KNX-002 were identified independently, they share a similar chemical scaffold. To determine why UCB-9721 is so much more potent than KNX-002 and to inform future development of this inhibitor class, we undertook comparative molecular docking analyses, targeted TgMyoA mutagenesis, and a directed structure-activity relationship analysis. The results identified the sulfonamide group of UCB-9721 and its hydrogen bond interactions with R249, E275 and a stabilized water network within the TgMyoA binding pocket as key to the compounds increased potency. Further development of UCB-9721, informed by the results presented here, may transform this promising new chemical class into actionable drug development leads against this important group of human and animal pathogens.

microbiology↗

bioRxiv2026

The CCCH-type zinc-finger PfMD3 promotes translation for malaria parasite transmission

Sexual maturation and fertility of the malaria causing parasite, Plasmodium spp., is critical to transmission between hosts. This developmental process involves an intricate gene expression regulatory network that drives gametocyte commitment, development, and the production of male and female gametes. Here, we characterized the role of the CCCH-type zinc-finger protein Plasmodium falciparum Male Development 3 (PfMD3) in the formation of gametes. Genetic disruption of PfMD3 revealed a male fertility defect that decreased infectivity to mosquitoes. Molecular characterization of PfMD3 revealed its binding to mRNA transcripts associated with male gamete development through a specific RNA sequence. Gametocyte proteins encoded by these PfMD3-bound transcripts decreased significantly in PfMD3 knockout parasites, suggesting that PfMD3 impacts translation. In addition to RNA-binding, PfMD3 also interacts with proteins involved in mRNA processing and nuclear export that influence translational regulation. This study establishes PfMD3 as an RNA-binding protein that impacts lineage-specific translation and male gamete fertility.

molecular biology↗

bioRxiv2026

A Plasmodium falciparum PX1 haplotype is associated with reduced susceptibility to artemisinin and lumefantrine

Effective control of falciparum malaria depends on the sustained efficacy of frontline antimalarial drugs, particularly artemether-lumefantrine (AL), the most widely used therapy in Africa. However, the emergence of artemisinin partial resistance and reduced lumefantrine susceptibility in eastern Africa threaten malaria control and elimination. Robust genetic markers of decreased susceptibility to lumefantrine remain elusive, and our understanding of artemisinin resistance is incomplete. We report results of a Plasmodium falciparum genetic cross between a drug-sensitive line and a Ugandan strain exhibiting reduced susceptibility to dihydroartemisinin and lumefantrine. Targeted deep sequencing of progeny pools and 460 recombinant progeny clones derived under drug pressures revealed distinct haplotypic signatures. Drug-selection experiments identified genetic polymorphisms in Plasmodium falciparum px1, encoding a phosphoinositide-binding protein, as the strongest correlates of reduced susceptibility to dihydroartemisinin and lumefantrine. The PX1 PIN haplotype (L1222P, M1701I, D1705N) recently discovered in Ugandan parasites was highly enriched following dihydroartemisinin or lumefantrine treatment of pooled mixtures of genetically diverse Ugandan clinical isolates. This haplotype was associated with reduced susceptibility to dihydroartemisinin and lumefantrine, compared to wild-type sequence, in culture-adapted Ugandan P. falciparum lines. These results confirm that PX1 mutations were selected across geographically distinct Ugandan parasite backgrounds. Long-term competitive fitness assays demonstrated that PX1 mutations confer asexual blood-stage parasites with a growth advantage, potentially explaining a rapid rise of PX1 PIN alleles over the last two decades in Uganda. Overall, our data suggest the PX1 PIN haplotype is a robust marker of reduced AL susceptibility in African P. falciparum, enabling surveillance of emerging drug resistance.

microbiology↗

bioRxiv2026

Dynamic regulation of long non-coding RNAs across asexual andgametocyte development in Plasmodium falciparum

Long non-coding RNAs (lncRNAs) are critical regulators of gene expression in eukaryotes. Short reads from Illumina sequencing, reverse transcriptase artefacts, and incomplete second-strand degradation in strand-specific cDNA libraries hamper genome-wide identification of lncRNAs, especially in gene-dense genomes such as Plasmodium. Here, we integrated long-read Oxford Nanopore Technology direct RNA sequencing, ribosome profiling, and single-cell transcriptomics to generate a robust and stage-specific characterization of P. falciparum lncRNAs. We generated comprehensive annotations of lncRNAs expressed in both asexual and sexual blood stages and confirmed their non-coding nature using ribosome profiling. Most lncRNAs showed pronounced stage-specific expression and appeared to be particularly abundant in mature gametocytes. Single-cell RNA sequencing revealed differential expression of many lncRNAs in female and male gametocytes, suggesting important roles in gametocytogenesis and transmission. Many lncRNAs are located antisense to protein-coding genes and are co-expressed with their sense mRNA, possibly from putative bidirectional promoters, while others overlap mRNA coding sequences or 3 untranslated regions and showed negatively correlated expression patterns. Overall, our study shows the prevalence of P. falciparum lncRNAs and highlights their possible roles in controlling the regulation of gene expression, particularly during gametocytogenesis.

genomics↗

bioRxiv2026

B Lymphocyte Protein Factories produced by Hematopoietic Stem Cell Gene Editing

Long-term in vivo production of therapeutic proteins and development of vaccines that elicit protective levels of broadly neutralizing antibodies (bNAbs) against major pathogens face challenges. Here we report on an alternative gene-editing approach using small numbers of hematopoietic stem and progenitor cells (HSPCs) to direct long-term, high-level expression of antibodies or cargo proteins. Edited B lymphocyte offspring can be activated by cognate antigen to undergo clonal expansion and develop into specific antibody or cargo protein-synthesizing plasma cells. These cells produce long-lasting, therapeutic levels of serum antibody against HIV-1 or malaria and an anti-influenza virus bNAb that mediated universal protection from heterologous lethal challenge. Our data provide a paradigm for cell therapy approaches to prevent or treat disease using self-amplifying B cell protein factories.

immunology↗

bioRxiv2025

High-Resolution Proteomics Unveils Salivary Gland Disruption and Saliva-Hemolymph Protein Exchange in Plasmodium-Infected Mosquitoes

Plasmodium sporozoites, the stage that initiates a malaria infection, must invade the mosquito salivary glands (SGs) before transmitting to a vertebrate host. However, the effects of sporozoite invasion on salivary gland physiology and saliva composition remain largely unexplored. We examined the impact of Plasmodium infection on Anopheles gambiae salivary glands using high-resolution proteomics, gene expression, and morphological analysis. The data revealed differential expression of various proteins, including the enrichment of humoral proteins in infected salivary glands originating from the hemolymph. These proteins diffused into the SGs due to structural damage caused by the sporozoites during invasion. Conversely, saliva proteins diffused out into the circulation of infected mosquitoes. Moreover, infection altered saliva protein composition, as shown by proteomes from saliva collected from mosquitoes infected by P. berghei or P. falciparum, revealing a significant reduction of immune proteins compared to uninfected mosquitoes. This reduction is likely due to the association of these proteins with the surface of sporozoites within the mosquito salivary secretory cavities. The saliva protein profiles from mosquitoes infected with both Plasmodium species were remarkably similar, suggesting a conserved interaction between sporozoites and salivary glands. Our results provide a foundation for understanding the molecular interactions between Plasmodium sporozoites and mosquito salivary glands.

microbiology↗

bioRxiv2025

Degradation of ribosomal RNA during Plasmodium falciparum gametocytogenesis

The life cycle of Plasmodium falciparum is characterized by complex regulatory changes that allow adaptation of the parasites to different environmental conditions, which are especially pronounced during transmission between the mammalian host and the insect vector. Previous studies have shown that P. falciparum uses three types of ribosomal RNAs (rRNA A-, S1- and S2-types) at different stages of its life cycle. We used Oxford Nanopore Technologies (ONT) direct RNA sequencing to investigate the dynamics of rRNA usage throughout the parasites intraerythrocytic development, as well as in salivary gland sporozoites. Our study revealed a preponderance of A-type rRNAs during the intraerythrocytic cycle and gametocytogenesis, while S-type rRNAs slowly increase in abundance in mosquito stages starting three days post infection. Salivary gland sporozoites showed an even proportion of all rRNA types. By examining the length distributions of rRNA molecules, we detected an extensive and specific degradation of rRNAs during gametocytogenesis, starting in stage II gametocytes and continuing until the final stages of gametocyte development. We hypothesize that rRNA degradation may be linked to the global translational repression and metabolic quiescence described in stage V gametocytes, similar to mechanisms observed in bacterial and eukaryotic stress responses.

microbiology↗

bioRxiv2024

Identification of the drug/metabolite transporter 1 as a marker of quinine resistance in a NF54xCam3.II P. falciparum genetic cross.

The genetic basis of Plasmodium falciparum resistance to quinine (QN), a drug used to treat severe malaria, has long been enigmatic. To gain further insight, we used FRG-NOD human liver-chimeric mice to conduct a P. falciparum genetic cross between QN-resistant (Cam3.II) and QN-sensitive (NF54) parasites, which also differ in their susceptibility to chloroquine (CQ). By applying different selective conditions to progeny pools prior to cloning, we recovered 120 unique recombinant progeny. Drug profiling and quantitative trait loci analyses of the progeny revealed predominant peaks on chromosomes 7 and 12 associated with CQ and QN resistance, that is consistent with a multifactorial mechanism of resistance for these compounds. CQ and monodesethyl-CQ (md-CQ) resistance mapped to a chromosome 7 region harboring pfcrt as expected. However, for QN, resistance mapped to a dominant chromosome 7 peak centered 295 kb downstream of pfcrt, with pfcrt showing a smaller peak. We identified the drug/metabolite transporter 1 (DMT1) as the top chromosome 7 candidate due to its structural similarity to PfCRT and proximity to the peak. Deleting DMT1 in QN-resistant Cam3.II parasites significantly sensitized the parasite to QN but not to the other drugs tested, suggesting that DMT1 mediates QN response specifically. We localized DMT1 to structures associated with vesicular trafficking, as well as the parasitophorous vacuolar membrane, lipid bodies, and the digestive vacuole. We also observed that mutant DMT1 transports more QN than the wild-type isoform in vitro. Gene editing confirmed an additional role for mutant PfCRT in mediating QN resistance. In addition, we identified an ATP-dependent zinc metalloprotease (FtsH1) as one of the top candidates in the chromosome 12 locus and confirmed its role as a potential mediator of QN resistance and a modulator of md-CQ resistance using CRISPR/Cas9 SNP-edited lines. Interestingly, this chromosome 12 region mapped to resistance to both CQ and QN and was preferentially co-inherited with pfcrt. Our study demonstrates that DMT1 is a novel marker of QN resistance and that a new chromosome 12 locus associates with CQ and QN response, with ftsh1 as a potential candidate, suggesting these genes in addition to pfcrt should be genotyped in surveillance and clinical settings.

genetics↗

bioRxiv2024

The major surface protein of malaria sporozoites is GPI-anchored to the plasma membrane

Glycosylphosphatidylinositol (GPI) anchor protein modification in Plasmodium species is well known and represents the principal form of glycosylation in these organisms. The structure and biosynthesis of GPI anchors of Plasmodium spp. has been primarily studied in the asexual blood stage of P. falciparum and is known to contain the typical conserved GPI structure of EtN-P-Man3GlcN-PI. Here, we have investigated the circumsporozoite protein (CSP) for the presence of a GPI-anchor. CSP is the major surface protein of Plasmodium sporozoites, the infective stage of the malaria parasite. While it is widely assumed that CSP is a GPI-anchored cell surface protein, compelling biochemical evidence for this supposition is absent. Here, we employed metabolic labeling and mass-spectrometry based approaches to confirm the presence of a GPI anchor in CSP. Biosynthetic radiolabeling of CSP with [3H]-palmitic acid and [3H]-ethanolamine, with the former being base-labile and therefore ester-linked, provided strong evidence for the presence of a GPI anchor on CSP, but these data alone were not definitive. To provide further evidence, immunoprecipitated CSP was analyzed for presence of myo-inositol (a characteristic component of GPI anchor) using strong acid hydrolysis and GC-MS for a highly sensitive and quantitative detection. The single ion monitoring (SIM) method for GC-MS analysis confirmed the presence of the myo-inositol component in CSP. Taken together, these data provide confidence that the long-assumed presence of a GPI anchor on this important parasite protein is correct.

biochemistry↗

bioRxiv2023

A transmission bottleneck for malaria? Quantification of sporozoite expelling from laboratory and natural P. falciparum infections

It is currently unknown whether all Plasmodium falciparum infected mosquitoes are equally infectious. We assessed sporogonic development using cultured gametocytes in the Netherlands and naturally circulating strains in Burkina Faso. We quantified the number of sporozoites expelled into artificial skin in relation to intact oocysts, ruptured oocysts, and residual salivary gland sporozoites. Sporozoites were quantified by highly sensitive qPCR; intact and ruptured oocysts by fluorescence microscopy following antibody staining of circumsporozoite protein. In laboratory conditions, higher total sporozoite burden in mosquitoes was associated with a shorter duration of sporogony (p<0.001). Overall, 53% (116/216) of P. falciparum infected An. stephensi mosquitoes expelled sporozoites into artificial skin. The medians of expelled and residual salivary gland sporozoites were 136 (IQR: 34-501) and 23,947 (IQR: 9127-78,380), respectively. There was a strong positive correlation between ruptured oocyst number and salivary gland sporozoite load ({rho}=0.8; p<0.0001) and a weaker positive correlation between salivary gland sporozoite load and the number of sporozoites expelled ({rho}=0.35; p=0.0002). In Burkina Faso, An. coluzzii mosquitoes were infected by natural gametocyte carriers. Among mosquitoes that were salivary gland sporozoite positive, 89% (33/37) expelled sporozoites with a median of 1035 expelled sporozoites (IQR: 171-2969) and harbored a median of 45,100 residual salivary gland sporozoites (IQR: 20,310-164,900). Again, we observed a strong correlation between ruptured oocyst number and salivary gland sporozoite load ({rho}=0.9; p<0.0001) and a positive correlation between salivary gland sporozoite load and the number of sporozoites expelled ({rho}=0.7; p<0.0001). Mosquito salivary glands in Burkina Faso harbored 1-3 distinct parasite clones; several mosquitoes expelled multiple parasite clones during probing. Whilst sporozoite expelling was regularly observed from mosquitoes with low infection burdens, our findings indicate that mosquito infection burden is associated with the number of expelled sporozoites. Future work is required to determine the direct implications of these findings for transmission potential.

microbiology↗

bioRxiv2023

Mapping the genomic landscape of multidrug resistance in Plasmodium falciparum and its impact on parasite fitness

Drug-resistant Plasmodium falciparum parasites have swept across Southeast Asia and now threaten Africa. By implementing a P. falciparum genetic cross using humanized mice, we report the identification of key determinants of resistance to artemisinin (ART) and piperaquine (PPQ) in the dominant Asian KEL1/PLA1 lineage. We mapped k13 as the central mediator of ART resistance and identified secondary markers. Applying bulk segregant analysis, quantitative trait loci mapping and gene editing, our data reveal an epistatic interaction between mutant PfCRT and multicopy plasmepsins 2/3 in mediating high-grade PPQ resistance. Susceptibility and parasite fitness assays implicate PPQ as a driver of selection for KEL1/PLA1 parasites. Mutant PfCRT enhanced susceptibility to lumefantrine, the first-line partner drug in Africa, highlighting a potential benefit of opposing selective pressures with this drug and PPQ. We also identified that the ABCI3 transporter can operate in concert with PfCRT and plasmepsins 2/3 in mediating multigenic resistance to antimalarial agents.

genomics↗

bioRxiv2023

Transmissibility of clinically relevant atovaquone-resistant Plasmodium falciparum by anopheline mosquitoes

Rising numbers of malaria cases and deaths underscore the need for new interventions. Long-acting injectable medications, such as those now in use for HIV prophylaxis, offer the prospect of a malaria "chemical vaccine", combining the efficacy of a drug (like atovaquone) with the durability of a biological vaccine. Of concern, however, is the possible selection and transmission of drug-resistant parasites. We addressed this question by generating clinically relevant, highly atovaquone-resistant, Plasmodium falciparum mutants competent to infect mosquitoes. Isogenic paired strains, that differ only by a single Y268S mutation in cytochrome b, were evaluated in parallel in southeast Asian (Anopheles stephensi) or African (Anopheles gambiae) mosquitoes, and thence in humanized mice. Fitness costs of the mutation were evident along the lifecycle, in asexual parasite growth in vitro and in a progressive loss of parasites in the mosquito. In numerous independent experiments, microscopic exam of salivary glands from hundreds of mosquitoes failed to detect even one Y268S sporozoite, a defect not rescued by coinfection with wild type parasites. Furthermore, despite uniformly successful transmission of wild type parasites from An. stephensi to FRG NOD huHep mice bearing human hepatocytes and erythrocytes, multiple attempts with Y268S-fed mosquitoes failed: there was no evidence of parasites in mouse tissues by microscopy, in vitro culture, or PCR. These studies confirm a severe-to-lethal fitness cost of clinically relevant atovaquone-resistant P. falciparum in the mosquito, and they significantly lessen the likelihood of their transmission in the field. SignificanceNew tools are needed to protect individuals from malaria and to control malaria in the field. Atovaquone plus proguanil is a commonly used and well-tolerated medicine to prevent malaria. No drug resistance has been reported from its prophylactic use, but tablets must be taken daily. Giving atovaquone as a single injection may provide much longer-lasting protection, against both falciparum and vivax malaria, but there is concern this may create drug resistance. In this study we showed that clinically relevant atovaquone-resistant malaria parasites survive poorly, if at all, in mosquitoes, and that mosquitoes do not transmit drug-resistant parasites to humanized mice. These findings lessen the likelihood that an atovaquone "chemical vaccine" would lead to the spread of atovaquone resistance.

microbiology↗

bioRxiv2022

Deciphering the non-coding code of pathogenicity and sexual differentiation in the human malaria parasite.

The complex life cycle of Plasmodium falciparum requires coordinated gene expression regulation to allow host cell invasion, transmission, and immune evasion. However, this cascade of transcripts is unlikely to be regulated by the limited number of identified parasite-specific transcription factors. Increasing evidence now suggests a major role for epigenetic mechanisms in gene expression in the parasite. In eukaryotes, many lncRNAs have been identified and shown to be pivotal regulators of genome structure and gene expression. To investigate the regulatory roles of lncRNAs in P. falciparum we explored the intergenic lncRNA distribution in nuclear and cytoplasmic subcellular locations. Using nascent RNA expression profiles, we identified a total of 1,768 lncRNAs, of which 58% were identified as novel lncRNAs in P. falciparum. The subcellular localization and stage-specific expression of several putative lncRNAs were validated using RNA fluorescence in situ hybridization (RNA-FISH). Additionally, the genome-wide occupancy of several candidate nuclear lncRNAs was explored using Chromatin Isolation by RNA Purification (ChIRP). ChIRP-seq of candidate lncRNAs revealed that lncRNA occupancy sites within the parasite genome are focal and sequence-specific with a particular enrichment for several parasite-specific gene families, including those involved in pathogenesis, erythrocyte remodeling, and regulation of sexual differentiation. We further validated the function of one specific lncRNA (lncRNA-ch14) using the CRISPR-Cas9 genome editing tool. Genomic and phenotypic analysis of the {bigtriangleup}lncRNA-ch14 line demonstrated the importance of this lncRNA in sexual differentiation and sexual reproduction. Our findings bring a new level of insight into the role of lncRNAs in pathogenicity, gene regulation and sexual differentiation. These findings also open new avenues for targeted approaches towards therapeutic strategies against the deadly malaria parasite.

microbiology↗

bioRxiv2022

Transport of Antibody into the Skin is Only Partially Dependent Upon the Neonatal Fc-Receptor

The dermis is the portal of entry for most vector-transmitted pathogens, making the hosts immune response at this site critical in mitigating the magnitude of infection. For malaria, antibody-mediated neutralization of Plasmodium parasites in the dermis was recently demonstrated. However, surprisingly little is known about the mechanisms that govern antibody transport into the skin. Since the neonatal Fc receptor (FcRn) has been shown to transcytose IgG into various tissues, we sought to understand its contribution to IgG transport and antibody-mediated inhibition of Plasmodium parasites following mosquito bite inoculation. Using confocal imaging, we show that the transport of an anti-Langerin mAb into the skin is only partially reduced in mice lacking FcRn. To understand the relevance of FcRn in the context of malaria infection, we use the rodent parasite Plasmodium berghei and show that the protective efficacy of a passively-administered anti-malarial antibody is reduced in the skin in FcRn deficient mice, but not to the same extent that we have previously observed in wildtype mice. Overall, our data suggest that FcRn plays a role in the transport of IgG into the skin but is not the major driver of IgG transport into this tissue. These findings have implications for the rational design of antibody-based therapeutics for malaria as well as other vector-transmitted pathogens.

immunology↗

bioRxiv2022

Screening the Pathogen Box Compounds for Activity Against Plasmodium falciparum Sporozoite Motility

As the malaria parasite becomes resistant to every drug that we develop, identification and development of novel drug candidates is essential. Many studies have screened compounds designed to target the clinically important blood stages. However, if we are to shrink the malaria map, new drugs that block transmission of the parasite are needed. Sporozoites are the infective stage of the malaria parasite, transmitted to the mammalian host as mosquitoes probe for blood. Sporozoite motility is critical to their ability to exit the inoculation site and establish infection and drug-like compounds targeting motility are effective in blocking infection in the rodent malaria model. In this study, we established a moderate throughput motility assay for sporozoites of the human malaria parasite Plasmodium falciparum, enabling us to screen the 400 drug-like compounds from the Pathogen box provided by Medicines for Malaria Venture for their activity. Compounds exhibiting inhibitory effects on P. falciparum sporozoite motility were further assessed against transmission-blocking activity and asexual stage growth. Five compounds had a significant inhibitory effect on P. falciparum sporozoite motility at 1 M concentration and four of these compounds also showed significant inhibition on transmission of P. falciparum gametocytes to the mosquito and of these four, three had previously been shown to have inhibitory activity on asexual blood stage parasites. Our findings provide new antimalarial drug candidates that have multi-stage activity.

microbiology↗

bioRxiv2021

The repeat region of the circumsporozoite protein is an elastic linear spring with a functional role in Plasmodium sporozoite motility

The circumsporozoite protein (CSP) forms a dense coat on the surface of the sporozoite, the infective stage of the malaria parasite. The central repeat region of CSP is a critical component of the only licensed malaria vaccine yet little is known about its structure or function. We found that sporozoite mutants with severely truncated or scrambled repeats have impaired motility due to altered adhesion site formation and dynamics, suggesting that the CSP repeats provide a cohesive environment in which adhesion sites can form. We hypothesized that biophysical properties of the repeats are important in this role and interrogated this using single-molecule fluorescence-force spectroscopy. We show that the repeats are a stiff, linear spring with elastic properties, dependent upon length and lost when the repeats are scrambled. These data are the first evidence that the CSP repeat region serves a functional role during infection and motility, likely mediated through its biophysical properties. SummaryNo clear function of the central repeat region of the malaria circumsporozoite protein has been described to date, despite its central role in the only licensed malaria vaccine. Here we use mutational analysis and single-molecule fluorescence-force spectroscopy to describe the structural properties and determine the function of this conserved region and important vaccine target. HighlightsThe CSP repeats have properties of a linear spring Scrambling or large truncations of the repeats leads to defects in sporozoite motility Motility defects are attributed to abnormal formation of adhesion sites

microbiology↗

bioRxiv2021

Altered cleavage of Caspase-1 in hepatocytes limits control of malaria in the liver

Malaria, caused by Plasmodium parasites, is a devastating disease that kills over half a million people each year1. Plasmodium sporozoites inoculated by mosquitoes into mammalian hosts undergo a clinically silent phase of obligatory development and replication in hepatocytes before initiating the life-threatening blood-stage of malaria2. Thus, understanding the immune responses elicited by Plasmodium infection in the liver is key to controlling clinical malaria and transmission3,4. Here, we show that Plasmodium DNA can be detected by AIM2 (absent in melanoma 2) sensors in the infected hepatocytes, resulting in Caspase-1 activation and pyroptotic cell-death. However, Caspase-1 was observed to undergo only partial cleavage in hepatocytes, limiting pyroptosis, and the maturation of pro-inflammatory cytokines classically associated with Caspase-1 activation. We discovered that the extent of Caspase-1 cleavage in cells is determined by the expression of ASC (apoptosis-associated speck-like protein containing a CARD). ASC expression is inherently low in hepatocytes, and transgenically enhancing it in the hepatocytes induced complete processing of Caspase-1, efficient secretion of pro-inflammatory cytokines, enhanced pyroptotic cell-death, and markedly improved control of malaria infection in the liver. In addition to describing a novel pathway of natural immunity to malaria, our findings uncover a key aspect of liver biology that may have been exploited during evolution by successful hepatotropic pathogens.

immunology↗

bioRxiv2019

Experimental Determination of the Force of Malaria Infection Reveals a Non-Linear Relationship to Mosquito Sporozoite Loads

Plasmodium sporozoites are the infective stage of the malaria parasite. Though this is a bottleneck for the parasite, the quantitative dynamics of transmission, from mosquito inoculation of sporozoites to patent blood-stage infection in the mammalian host, are poorly understood. Here we utilize a rodent model to determine the probability of malaria infection after infectious mosquito bite, and consider the impact of mosquito parasite load, blood-meal acquisition, probe-time, and probe location, on infection probability. We found that infection likelihood correlates with mosquito sporozoite load and, to a lesser degree, the duration of probing, and is not dependent upon the mosquitos ability to find blood. The relationship between sporozoite load and infection probability is non-linear and can be described by a set of models that include a threshold, with mosquitoes harboring over 10,000 salivary gland sporozoites being 7.5 times more likely to initiate a malaria infection. Overall, our data suggest that the small subset of highly infected mosquitoes may contribute disproportionally to malaria transmission in the field and that quantifying mosquito sporozoite loads could aid in predicting the force of infection in different transmission settings.\n\nAuthor SummaryMalaria is a leading cause of death in many parts of the world. Infection is initiated when infected Anopheles mosquitoes inject sporozoites as they look for blood. Though transmission is a bottleneck for the parasite and thus a good point for intervention, many aspects of transmission remain poorly understood. In this study, using a rodent model of malaria, we found that less than 20% of infectious bites result in disease, demonstrating that the majority of infective bites do not result in malaria infection. Furthermore, we found that the bites of mosquitoes with heavy parasite burdens are 7.5 times more likely to result in disease. These data have important implications for designing interventions targeting transmission stages of the malaria parasite as they suggest that reducing parasite loads, even without completely eliminating them, could be effective against disease spread. We also found that mosquitoes that probe but do not succeed in finding blood are equally likely to initiate infection, an important finding for human vaccine trials. Together, this work adds to our understanding of malaria transmission dynamics and our capacity to develop malaria elimination strategies.

microbiology↗