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Introduction: Concomitant risk factors challenge the mechanistic understanding of cardiac aging. We determined the degree to which the left atrial function could be distinguished by advanced cardiac magnetic resonance (CMR) imaging in older adults and assessed associations between the left atrial function and the plasma biomarkers related to biological aging and cardiovascular disease [serum monocyte chemoattractant protein-1 (MCP1), matrix metallopeptidase 9 (MMP-9), B-type natriuretic peptides (BNPs), galectin-3 (Gal-3), high-sensitivity cardiac troponin I (hsTn1), high-sensitivity C-reactive protein (hs-CRP), and soluble urokinase plasminogen activator receptor (sUPAR)]. Methods: Among a cross-sectional population-based cohort of older adults, longitudinal LA strain including reservoir strain (ϵs), conduit strain (ϵe), and booster strain (ϵa) as well as peak strain rates (SRs, SRe, SRa) were determined using CMR and studied in association with blood biomarkers. Results: We studied 243 community adults (42.8% female, mean age 70.3 ± 9.5 years). In bivariate analysis, ϵe and SRe were reduced in gradation with increasing risk factors (all p values

Efforts to develop vaccines against malaria represent a major research target. The observations that 1) sterile protection can be obtained when the host is exposed to live parasites and 2) the immunity against blood stage parasite is principally mediated by protective antibodies suggest that a protective vaccine is feasible. However, only a small number of proteins have been investigated so far and most of the Plasmodium proteome has yet to be explored. To date, only few immunodominant antigens have emerged for testing in clinical trials but no formulation has led to substantial protection in humans. The nature of parasite molecules associated with protection remains elusive. Here, immunomic screening of mice immune sera with different protection efficiencies against the whole parasite proteome allowed us to identify a large repertoire of antigens validated by screening a library expressing antigens. The calculation of weighted scores reflecting the likelihood of protection of each antigen using five predictive criteria derived from immunomic and proteomic data sets, highlighted a priority list of protective antigens. Altogether, the approach sheds light on conserved antigens across Plasmodium that are amenable to targeting by the host immune system upon merozoite invasion and blood stage development. Most of these antigens have preliminary protection data but have not been widely considered as candidate for vaccine trials, opening new perspectives that overcome the limited choice of immunodominant, poorly protective vaccines currently being the focus of malaria vaccine researches. NMRC (Natl Medical Research Council, S’pore) MOH (Min. of Health, S’pore) Accepted version

Numerous reports of vascular events after an initial recovery from COVID-19 form our impetus to investigate the impact of COVID-19 on vascular health of recovered patients. We found elevated levels of circulating endothelial cells (CECs), a biomarker of vascular injury, in COVID-19 convalescents compared to healthy controls. In particular, those with pre-existing conditions (e.g., hypertension, diabetes) had more pronounced endothelial activation hallmarks than non-COVID-19 patients with matched cardiovascular risk. Several proinflammatory and activated T lymphocyte-associated cytokines sustained from acute infection to recovery phase, which correlated positively with CEC measures, implicating cytokine-driven endothelial dysfunction. Notably, we found higher frequency of effector T cells in our COVID-19 convalescents compared to healthy controls. The activation markers detected on CECs mapped to counter receptors found primarily on cytotoxic CD8+ T cells, raising the possibility of cytotoxic effector cells targeting activated endothelial cells. Clinical trials in preventive therapy for post-COVID-19 vascular complications may be needed. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Ministry of Health (MOH) Nanyang Technological University National Medical Research Council (NMRC) National Research Foundation (NRF) Published version This research is funded by National Medical Research Council (COVID19RF-001, COVID19RF-060, NMRC/TA/0031/2015, MOH-000153, NMRC/OFIRG/0018/2016, NMRC/BnB/0017/2015, MOH-000358), Biomedical Research Council, A*STAR (H20/04/g1/006), National Research Foundation Singapore (NRF2017_SISFP09), Nanyang Technological University (Nanyang Assistant Professorship Start-Up Grant), Ministry of Education - Singapore (MOE2018-T2-1-042) and Agency for Science, Technology and Research (H18/01/a0/017).

The rapid rise of coronavirus disease 2019 patients who suffer from vascular events after their initial recovery is expected to lead to a worldwide shift in disease burden. We aim to investigate the impact of COVID-19 on the pathophysiological state of blood vessels in convalescent patients. Here, convalescent COVID-19 patients with or without preexisting conditions (i.e. hypertension, diabetes, hyperlipidemia) were compared to non-COVID-19 patients with matched cardiovascular risk factors or healthy participants. Convalescent patients had elevated circulating endothelial cells (CECs), and those with underlying cardiovascular risk had more pronounced endothelial activation hallmarks (ICAM1, P-selectin or CX3CL1) expressed by CECs. Multiplex microbead-based immunoassays revealed some levels of cytokine production sustained from acute infection to recovery phase. Several proinflammatory and activated T lymphocyte-associated cytokines correlated positively with CEC measures, implicating cytokine-driven endothelial dysfunction. Finally, the activation markers detected on CECs mapped to the counter receptors (i.e. ITGAL, SELPLG, and CX3CR1) found primarily on CD8+ T cells and natural killer cells, suggesting that activated endothelial cells could be targeted by cytotoxic effector cells. Clinical trials in preventive therapy for post-COVID-19 vascular complications may be needed.Graphical abstract

COVID-19 management guidelines have largely attributed critically ill patients who develop acute respiratory distress syndrome, to a systemic overproduction of pro-inflammatory cytokines. Cardiovascular dysfunction may also represent a primary phenomenon, with increasing data suggesting that severe COVID-19 reflects a confluence of vascular dysfunction, thrombosis and dysregulated inflammation. Here, we first consolidate the information on localized microvascular inflammation and disordered cytokine release, triggering vessel permeability and prothrombotic conditions that play a central role in perpetuating the pathogenic COVID-19 cascade. Secondly, we seek to clarify the gateways which SARS-CoV-2, the causative COVID-19 virus, uses to enter host vascular cells. Post-mortem examinations of patients' tissues have confirmed direct viral endothelial infection within several organs. While there have been advances in single-cell RNA sequencing, endothelial cells across various vascular beds express low or undetectable levels of those touted SARS-CoV-2 entry factors. Emerging studies postulate alternative pathways and the apicobasal distribution of host cell surface factors could influence endothelial SARS-CoV-2 entry and replication. Finally, we provide experimental considerations such as endothelial polarity, cellular heterogeneity in organoids and shear stress dynamics in designing cellular models to facilitate research on viral-induced endothelial dysfunctions. Understanding the vascular underpinning of COVID-19 pathogenesis is crucial to managing outcomes and mortality. Published version

The development of an effective malaria vaccine has remained elusive even until today. This is because of our incomplete understanding of the immune mechanisms that confer and/or correlate with protection. Human volunteers have been protected experimentally from a subsequent challenge by immunization with Plasmodium falciparum sporozoites under drug cover. Here, we demonstrate that sera from the protected individuals contain neutralizing antibodies against the pre-erythrocytic stage. To identify the antigen(s) recognized by these antibodies, a newly developed library of P. falciparum antigens was screened with the neutralizing sera. Antibodies from protected individuals recognized a broad antigenic repertoire of which three antigens, PfMAEBL, PfTRAP and PfSEA1 were recognized by most protected individuals. As a proof of principle, we demonstrated that anti-PfMAEBL antibodies block liver stage development in human hepatocytes. Thus, these antigens identified are promising targets for vaccine development against malaria.

Summary Development of the erythrocytic malaria parasite requires targeting of parasite proteins into multiple compartments located within and beyond the para- site confine. Beyond the PEXEL/VTS pathway and its characterized players, increasing amount of evidence has highlighted the existence of pro- teins exported using alternative export-signal(s)/ pathway(s); hence, the exportomes currently pre- dicted are incomplete. The nature of these ex- ported proteins which could have a prominent role in most of the Plasmodium species remains elusive. Using P. yoelii variant proteins, we identi- fied a signal associated to lipophilic region that mediates export of P. yoelii proteins. This non- PEXEL signal termed PLASMED is defined by semi-conserved residues and possibly a second- ary structure. In vivo characterization of exported- proteins indicated that PLASMED is a bona fide export-signal that allowed us to identify an unseen P. yoelii exportome. The repertoire of the newly predicted exported proteins opens up perspec- tives for unravelling the remodelling of the host- cell by the parasite, against which new therapies could be elaborated.

Scientific Reports 6: Article number: 31055; published online: 09 August 2016; updated: 21 November 2016.

Plasmodium associated virulence in the host is linked to extensive remodelling of the host erythrocyte by parasite proteins that form the “remodellome”. However, without a common motif or structure available to identify these proteins, little is known about the proteins that are destined to reside in the parasite periphery, the host-cell cytoplasm and/or the erythrocyte membrane. Here, the subcellular fractionation of erythrocytic P. yoelii at trophozoite and schizont stage along with label-free quantitative LC-MS/MS analysis of the whole proteome, revealed a proteome of 1335 proteins. Differential analysis of the relative abundance of these proteins across the subcellular compartments allowed us to map their locations, independently of their predicted features. These results, along with literature data and in vivo validation of 61 proteins enabled the identification of a remodellome of 184 proteins. This approach identified a significant number of conserved remodelling proteins across plasmodium that likely represent key conserved functions in the parasite and provides new insights into parasite evolution and biology.

An effective antibody response can assist drug treatment to contribute to better parasite clearance in malaria patients. To examine this, sera were obtained from two groups of adult patients with acute falciparum malaria, prior to drug treatment: patients who (1) have subsequent recrudescent infection, or (2) were cured by Day 28 following treatment. Using a Plasmodium falciparum antigen library, we examined the antibody specificities in these sera. While the antibody repertoire of both sera groups was extremely broad and varied, there was a differential antibody profile between the two groups of sera. The proportion of cured patients with antibodies against EXP1, MSP3, GLURP, RAMA, SEA and EBA181 was higher than the proportion of patients with recrudescent infection. The presence of these antibodies was associated with higher odds of treatment cure. Sera containing all six antibodies impaired the invasion of P. falciparum clinical isolates into erythrocytes. These results suggest that antibodies specific against EXP1, MSP3, GLURP, RAMA, SEA and EBA181 in P. falciparum infections could assist anti-malarial drug treatment and contribute to the resolution of the malarial infection. Published version

Plasmodium multigene families play a central role in the pathogenesis of malaria. The Plasmodium interspersed repeat (pir) genes comprise the largest multigene family in many Plasmodium spp. However their function(s) remains unknown. Using the rodent model of malaria, Plasmodium chabaudi, we show that individual CIR proteins have differential localizations within infected red cell (iRBC), suggesting different functional roles in a blood-stage infection. Some CIRs appear to be located on the surface of iRBC and merozoites and are therefore well placed to interact with host molecules. In line with this hypothesis, we show for the first time that a subset of recombinant CIRs bind mouse RBCs suggesting a role for CIR in rosette formation and/or invasion. Together, our results unravel differences in subcellular localization and ability to bind mouse erythrocytes between the members of the cir family, which strongly suggest different functional roles in a blood-stage infection.

Background. Severe malaria and one of its most important pathogenic processes, cerebral malaria, involves the sequestration of parasitized red blood cells (pRBCs) in brain postcapillary veinules. Although the pathogenic mechanisms underlying malaria remain poorly characterized, it has been established that adhesion of pRBCs to endothelial cells (ECs) can result in cell apoptosis, which in turn may lead to disruption of the blood-brain barrier. The nature of the parasite molecules involved in the pathogenesis of severe malaria remains elusive. Methods. Whole-transcriptome profiling of nonapoptogenic versus apoptogenic parasite field isolates obtained from Gabonese children was performed with pan-genomic Plasmodium faldparum DNA microarrays; radiolabeled instead of fluorescent cDNAs were used to improve the sensitivity of signal detection. Results. Our methods allowed the identification of 59 genes putatively associated with the induction of EC apoptosis. Silencing of Plasmodium gene expression with specific double-stranded RNA was performed on 8 selected genes; 5 of these, named "Plasmodium apoptosis-linked pathogenicity factors" (PALPFs), were found to be linked to parasite apoptogenicity. Of these genes, 2 might act via parasite cytoadherence. Conclusion. This is the first attempt to identify genes involved in parasite pathogenic mechanisms against human ECs. The finding of PALPFs illuminates perspectives for novel therapeutic strategies against cerebral complications of malaria.

Development of the erythrocytic malaria parasite requires targeting of parasite proteins into multiple compartments located within and beyond the parasite confine. Beyond the PEXEL/VTS pathway and its characterized players, increasing amount of evidence has highlighted the existence of proteins exported using alternative export-signal(s)/pathway(s); hence, the exportomes currently predicted are incomplete. The nature of these exported proteins which could have a prominent role in most of the Plasmodium species remains elusive. Using P. yoelii variant proteins, we identified a signal associated to lipophilic region that mediates export of P. yoelii proteins. This non-PEXEL signal termed PLASMED is defined by semi-conserved residues and possibly a secondary structure. In vivo characterization of exported-proteins indicated that PLASMED is a bona fide export-signal that allowed us to identify an unseen P. yoelii exportome. The repertoire of the newly predicted exported proteins opens up perspectives for unravelling the remodelling of the host-cell by the parasite, against which new therapies could be elaborated.

A key step for the survival of the malaria parasite is the release from and subsequent invasion of erythrocytes by the merozoite. Differences in the efficiency of these two linked processes have a direct impact on overall parasite burden in the host and thereby virulence. A number of parasite proteases have recently been shown to play important roles during both merozoite egress as well as merozoite invasion. The rodent malaria parasite Plasmodium yoelii has been extensively used to investigate the mechanisms of parasite virulence in vivo and a number of important proteins have been identified as being key contributors to pathology. Here we have utilized transcriptional comparisons to identify two protease-like SERAs as playing a potential role in virulence. We show that both SERAs are non-essential for blood stage development of the parasite though they provide a subtle but important growth advantage in vivo. In particular SERA2 appears to be an important factor in enabling the parasite to fully utilize the whole age repertoire of circulating erythrocytes. This work for the first time demonstrates the subtle contributions different protease-like SERAs make to provide the parasite with a maximal capacity to successfully maintain an infection in the host. Published version

Plasmodium sporozoites are deposited in the skin by Anopheles mosquitoes. They then find their way to the liver, where they specifically invade hepatocytes in which they develop to yield merozoites infective to red blood cells. Relatively little is known of the molecular interactions during these initial obligatory phases of the infection. Recent data suggested that many of the inoculated sporozoites invade hepatocytes an hour or more after the infective bite. We hypothesised that this pre-invasive period in the mammalian host prepares sporozoites for successful hepatocyte infection. Therefore, the genes whose expression becomes modified prior to hepatocyte invasion would be those likely to code for proteins implicated in the subsequent events of invasion and development. We have used P. falciparum sporozoites and their natural host cells, primary human hepatocytes, in in vitro co-culture system as a model for the pre-invasive period. We first established that under co-culture conditions, sporozoites maintain infectivity for an hour or more, in contrast to a drastic loss in infectivity when hepatocytes were not included. Thus, a differential transcriptome of salivary gland sporozoites versus sporozoites co-cultured with hepatocytes was established using a pan-genomic P. falciparum microarray. The expression of 532 genes was found to have been up-regulated following co-culture. A fifth of these genes had no orthologues in the genomes of Plasmodium species used in rodent models of malaria. Quantitative RT-PCR analysis of a selection of 21 genes confirmed the reliability of the microarray data. Time-course analysis further indicated two patterns of up-regulation following sporozoite co-culture, one transient and the other sustained, suggesting roles in hepatocyte invasion and liver stage development, respectively. This was supported by functional studies of four hitherto uncharacterized proteins of which two were shown to be sporozoite surface proteins involved in hepatocyte invasion, while the other two were predominantly expressed during hepatic parasite development. The genome-wide up-regulation of expression observed supports the hypothesis that the shift from the mosquito to the mammalian host contributes to activate quiescent salivary gland sporozoites into a state of readiness for the hepatic stages. Functional studies on four of the up-regulated genes validated our approach as one means to determine the repertoire of proteins implicated during the early events of the Plasmodium infection, and in this case that of P. falciparum, the species responsible for the severest forms of malaria., Author Summary Sporozoites, the infective form of the malaria parasites Plasmodium, are deposited in the skin by Anopheles mosquitoes. They then find their way to the liver where they specifically invade hepatocytes, in which they develop to yield another form, the merozoite, infective to red blood cells. Relatively little is known of the molecular interactions during these initial obligatory phases of the infection. We studied the changes in gene expression in sporozoites, from the parasite species P. falciparum that infects humans, in an in vitro system where they were co-cultured with their natural host cells, primary human hepatocytes. The whole genome transcriptome profiling carried out led to the identification of 532 genes that were up-regulated following co-culture. This genome-wide up-regulation of expression supports the hypothesis that the shift from the mosquito to the mammalian host contributes to activate quiescent salivary gland sporozoites into a state of readiness for the hepatic stages. Functional studies on four of the up-regulated genes we identified validated our approach as one means to determine the repertoire of proteins implicated during the early events in the infection by P. falciparum, the species responsible for the severest forms of malaria.

Contains fulltext : 71106.pdf (Publisher’s version ) (Closed access) Infection of hepatocytes by Plasmodium falciparum sporozoites requires the host tetraspanin CD81. CD81 is also predicted to be a coreceptor, along with scavenger receptor BI (SR-BI), for hepatitis C virus. Using SR-BI-knockout, SR-BI-hypomorphic and SR-BI-transgenic primary hepatocytes, as well as specific SR-BI-blocking antibodies, we demonstrate that SR-BI significantly boosts hepatocyte permissiveness to P. falciparum, P. yoelii, and P. berghei entry and promotes parasite development. We show that SR-BI, but not the low-density lipoprotein receptor, acts as a major cholesterol provider that enhances Plasmodium infection. SR-BI regulates the organization of CD81 at the plasma membrane, mediating an arrangement that is highly permissive to penetration by sporozoites. Concomitantly, SR-BI upregulates the expression of the liver fatty-acid carrier L-FABP, a protein implicated in Plasmodium liver-stage maturation. These findings establish the mechanistic basis of the CD81-dependent Plasmodium sporozoite invasion pathway.

Background The global spread of multidrug–resistant malaria parasites has led to an urgent need for new chemotherapeutic agents. Drug discovery is primarily directed to the asexual blood stages, and few drugs that are effective against the obligatory liver stages, from which the pathogenic blood infection is initiated, have become available since primaquine was deployed in the 1950s. Methods and Findings Using bioassay-guided fractionation based on the parasite's hepatic stage, we have isolated a novel morphinan alkaloid, tazopsine, from a plant traditionally used against malaria in Madagascar. This compound and readily obtained semisynthetic derivatives were tested for inhibitory activity against liver stage development in vitro (P. falciparum and P. yoelii) and in vivo (P. yoelii). Tazopsine fully inhibited the development of P. yoelii (50% inhibitory concentration [IC50] 3.1 μM, therapeutic index [TI] 14) and P. falciparum (IC50 4.2 μM, TI 7) hepatic parasites in cultured primary hepatocytes, with inhibition being most pronounced during the early developmental stages. One derivative, N-cyclopentyl-tazopsine (NCP-tazopsine), with similar inhibitory activity was selected for its lower toxicity (IC50 3.3 μM, TI 46, and IC50 42.4 μM, TI 60, on P. yoelii and P. falciparum hepatic stages in vitro, respectively). Oral administration of NCP-tazopsine completely protected mice from a sporozoite challenge. Unlike the parent molecule, the derivative was uniquely active against Plasmodium hepatic stages. Conclusions A readily obtained semisynthetic derivative of a plant-derived compound, tazopsine, has been shown to be specifically active against the liver stage, but inactive against the blood forms of the malaria parasite. This unique specificity in an antimalarial drug severely restricts the pressure for the selection of drug resistance to a parasite stage limited both in numbers and duration, thus allowing researchers to envisage the incorporation of a true causal prophylactic in malaria control programs., A derivative of a morphinan alkaloid, tazopsine, from a plant used against malaria in Madagascar, is active against the hepatic stages ofPlasmodium species., Editors' Summary Background. The parasite that causes malaria has quickly developed resistance to many of the drugs that are commonly used to treat this disease. As a result, new drugs and drug combinations are needed. In some parts of the world where antimalarial drugs are failing due to resistance, or are not available to everyone, people often turn to traditional herbal remedies instead. These traditional plant remedies can be a useful starting point for development of new drugs, but the process of developing effective new drugs from plant remedies is long and complicated. An important initial step is to isolate and identify the active compounds from plants and then see how well these compounds perform against malaria parasites in laboratory tests. If the tests are successful, such compounds could then progress to experiments in animals and possibly eventually human trials. One plant used widely in Madagascar for treatment of malaria is Strychnopsis thouarsii; the traditional remedy consists of the plant stem bark boiled in water. Why Was This Study Done? The group of researchers doing this study wanted to discover candidates for new malaria drugs. They therefore wanted to find out which molecular compounds in the stem bark of S. thouarsii contained antimalarial activity, and what particular stage of the malaria parasite's life cycle these compounds had an effect on. The researchers suspected that the agents in this plant bark had some activity against the “liver stage” of malaria infection in humans. This is the first stage of infection, after a person has been bitten by a malaria-infected mosquito, and before blood cells are invaded by malaria parasites (which then causes the disease symptoms). Very few drugs currently in existence have an effect on the “liver stage” of infection, but activity at this stage would be tremendously useful because it could mean a drug is better for prevention of malaria than others in existence. What Did the Researchers Do and Find? First, the researchers wanted to take the traditional herbal remedy—of S. thouarsii bark boiled in water—and find out precisely which molecule in that remedy was responsible for the antimalarial activity. They therefore used a method called chromatography to progressively separate the herbal extract into its distinct components. At each stage of separation, the extract was checked for activity against malaria using a laboratory test. Inactive extracts were disregarded, and the active component then taken on to a further separation round. After many rounds of separation and testing, the researchers got down to a single, apparently new, molecule that was active against malaria in the laboratory test, and this molecule was named tazopsine (in the Malagasy language the word Tazo refers to malaria). In order to find out how effective the molecule was at killing malaria parasites, the researchers took human or mouse liver cells cultured in the laboratory, infected them with malaria parasites (either the malaria parasite that normally infects humans, or a related species that infects mice), and then added tazopsine at different concentrations. The compound completely killed the malaria parasites even at very low concentrations, and had activity against malaria infecting either liver cells or red blood cells. Tazopsine was then given to mice injected with a species of the malaria parasite. The compound protected most mice against malaria infection when it was used at a dosage level lower than the toxic dose. The researchers then tried making a series of different variants of tazopsine in the hope that some variants would be less toxic, but equally active as, the original compound. They found one variant, named NCP-tazopsine, that was much less toxic but just as active as tazopsine, but only against the malaria infecting liver cells. What Do These Findings Mean? In these experiments a new molecule, tazopsine, was discovered from a Malagasy plant, and it was found to be active against liver-stage malaria parasites, in laboratory experiments and in mice. This molecule or variants of it could in future become candidate antimalarial drugs in humans. However, much work would need to be done before testing could get to that stage. Different variants of molecules related to tazopsine would need to be tested to find one that has low toxicity, and these variants would need to be fully evaluated in animals to see how they are handled in the body before any trials could begin in humans. Additional Information. Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0030513 The World Health Organization publishes a minisite containing links to information about all aspects of malaria worldwide, including treatment, prevention, and current programmes for malaria control Medicines for Malaria Venture is a collaboration between public and private organizations (including the pharmaceutical industry) that aims to fund and manage the development of new drugs for treatment and prevention of malaria Wikipedia entries for drug discovery and drug development (note: Wikipedia is an internet encyclopedia that anyone can edit)

Item does not contain fulltext The CSP, EMP2/MESA, MSP2, MSP3, MSP5, RAP1, RAP2, RESA1, SERA1 and SSP2/TRAP genes of Plasmodium falciparum are vaccine candidates. The hepatic phase of the infection is of major interest due to the protection induced by immunization with radiation-attenuated sporozoites. We therefore performed RT-PCR experiments to determine whether these genes are transcribed during this phase. Whereas transcripts of the CSP gene were detectable only in sporozoites, transcripts of the MSP2, MSP5, RAP1, RAP2, SERA1 and SSP2/TRAP genes were present in both sporozoites and infected hepatocytes. Transcripts of the EMP2/MESA gene were detectable only in infected hepatocytes. Transcripts of the MSP3 and RESA1 genes were not detectable in sporozoites or in infected hepatocytes. Genes presently identified as being transcribed during the hepatic phase may be of interest with respect to the design of preventative vaccination strategies.

Plasmodium sporozoites are transmitted through the bite of infected mosquitoes and invade hepatocytes as a first and obligatory step of the parasite life cycle in man. Hepatocyte invasion involves proteins secreted from parasite vesicles called micronemes, the most characterized being the thrombospondin-related adhesive protein (TRAP). Here we investigated the expression and function of another microneme protein recently identified in Plasmodium falciparum sporozoites, apical membrane antigen 1 (AMA-1). P. falciparum AMA-1 is expressed in sporozoites and is lost after invasion of hepatocytes, and anti-AMA-1 antibodies inhibit sporozoite invasion, suggesting that the protein is involved during invasion of hepatocytes. As observed with TRAP, AMA-1 is initially mostly sequestered within the sporozoite. Upon microneme exocytosis, AMA-1 and TRAP relocate to the sporozoite surface, where they are proteolytically cleaved, resulting in the shedding of soluble fragments. A subset of serine protease inhibitors blocks the processing and shedding of both AMA-1 and TRAP and inhibits sporozoite infectivity, suggesting that interfering with sporozoite proteolytic processing may constitute a valuable strategy to prevent hepatocyte infection.