As the BioMalPar conference marks its 20th anniversary, we celebrate two decades of pioneering research and collaboration in the battle against malaria. This milestone is a testament to the relentless pursuit of knowledge about the Plasmodium parasite, its interactions with hosts and vectors, and the ongoing quest to develop effective intervention strategies.

This year, the conference was not just a reflection on past achievements but a vibrant exchange of ideas, where scientists from around the world connected to push the boundaries of our understanding. Among the many highlights of the event, the poster prize winners stood out for their innovative contributions to malaria research.

In this post, we are excited to spotlight four of these outstanding winners, whose work exemplifies the cutting-edge research being conducted in the field. Congratulations to Inês, Samuel, Ana Maria, and Lauren!

Liver stage replication: finding a new path to thousands

Presenter: Inês Bento 

Authors: Inês Bento, Nuno Leal, Mónica Galocha, Rita Tewari, Maria Mota, Sabrina Absalon

Abstract:

Malaria imposes an immense public health and economic burden on large parts of the world. Expanding the knowledge on the fundamental principles orchestrating Plasmodium basic biology, the causative agent of malaria, may prove paramount in the ongoing battle against this life-threatening disease.

Once inside a hepatocyte, parasites replicate at an intriguingly high rate generating thousands of new erythrocyte-infectious forms. Despite the critical role of the intra-hepatic phase in successfully establishing infection, how parasites replicate within the hepatocyte remains unexplored.

The use of ultrastructure expansion microscopy revealed a groundbreaking observation that Plasmodium replication inside hepatocytes involves ENDOPOLYGENY – consecutive rounds of DNA replication without nuclear separation resulting in polyploid nuclei – followed by SCHIZOGONY, with the concomitant individualization of the nuclei and a final phase of cellularization. This challenges the current dogma on Plasmodium replication which is considered to occur exclusively via schizogony as observed during a blood stage infection.

Additionally, we show that in the absence of methionine, an essential amino acid, parasites replicate exclusively via endopolygeny, suggesting that parasite’s replication strategies during liver stage are adaptable, responding to host nutritional status.

Altogether, this led us to hypothesize that endopolygeny followed by schizogony is a strategy parasites use to ensure a high progeny. Thus, we are currently: i) quantifying the newly formed genomes during endopolygeny versus schizogony (by droplet digital PCR); ii) ascertain parasite’s nuclear organization by ultrastructural expansion microscopy; and ii) identifying the molecular players in Plasmodium cell cycle that dictate the distinct liver stage replication strategies, by performing a functional reverse genetic screen for kinases as putative cell cycle regulators.

By uncovering the ultrastructural and molecular details behind the uniqueness of Plasmodium’s liver stage replication, we gain valuable insights into new intervention targets and strategies to reduce parasite biomass that ultimately bring us closer to the goal of eradicating malaria worldwide.

Due to the confidentiality of the unpublished data, we cannot share the poster.

The evolutionary battle between Plasmodium falciparum and NK cells of the innate immune system: RIFINs engage, and signal through, both KIR2DL1 and KIR2DS1

Presenter: Samuel Chamberlain

Authors: Samuel Chamberlain, Shiroh Iwanaga, Matt Higgins, Alexander Mørch, Arase Hisashi, Thomas Harrison, Michael Dustin, Akihito Sakoguchi

Abstract:

Natural Killer (NK) cells of the innate immune system are armed with inhibitory and
activatory immune receptors. These receptors enable them to discriminate between our own cells and those which pose harm to the body, including pathogens and pathogen-infected or damaged cells. Some immune receptors such as the KIRs (Killer Immunoglobulin-like Receptors) exist as paired receptors, with both long (L) and short (S) intracellular tails, that can mediate either inhibitory or activatory signalling, respectively. The balance of signalling through these receptors determines whether NK cells are activated and target cells are destroyed. RIFINs, the largest family of variable surface antigen proteins in Plasmodium falciparum, are displayed on the surface of the infected erythrocytes. Previous studies have shown that RIFINs can bind to inhibitory immune receptors and dampen NK cell activation, which potentially reduces parasite clearance. Here, we identify a clade of RIFINs that bind to the inhibitory receptor KIR2DL1. We show that this interaction mediates inhibitory signalling and that NK cell activation is reduced as a result. We use structural studies to reveal the molecular basis for the interaction between the RIFIN and KIR2DL1 and show that the utilised interface is conserved between KIR2DL1 and the activatory KIR2DS1 receptor. Indeed, we show that the same RIFIN can bind to, and signal through, KIR2DS1, leading to the activation of KIR2DS1-expressing NK cells. This study highlights the evolutionary battle between pathogen and host, suggesting that activatory KIRs have evolved to allow the detection of Plasmodium falciparum infected erythrocytes, countering the immune-evasion strategies of the parasite and improving host clearance mechanisms.

View poster

Unravelling the role of calcium-dependent protein kinases in Babesia divergens lifecycle

Presenter: Ana Maria Filipe

Authors: Ana Maria Filipe, Adéla Chlastáková, Alper Dede, Tereza Žirovnická, Daniel Sojka, Marie Jalovecka

Abstract:

Babesia divergens is a tick-transmitted parasite commonly found in Europe as an economically important agent of bovine babesiosis and a life-threatening zoonosis in humans. Central to its pathogenesis is parasitism inside host erythrocytes – an ability shared with its apicomplexan relative Plasmodium, the causative agent of malaria. The parasite invasion to host cells and subsequent intracellular multiplication are orchestrated by a wide repertoire of molecules including the calcium-dependent protein kinases (CDPKs). We focus on the unbiased screen of yet unrevealed Babesia divergens CDPKs and their association with fundamental biological processes in the lifecycle of this parasite. B. divergens was cultivated in vitro in bovine erythrocytes and adult Ixodes ricinus females acquired this parasite through an artificial feeding technique. Two distinct experiments were conducted to evaluate BdCDPKs role during the B. divergens life cycle: one involving sorted and synchronized intra-erythrocytic parasite stages the other using infected tick tissues (salivary glands, ovaries and gut epithelial cells). The relative expression of BdCDPKs was quantified in collected cDNA templates using multiplex qPCR, employing the ΔCt method, and normalized to B. divergens reference genes, gapdh (Bdiv_010720) and actin (Bdiv_007890). Throughout the intra-erythrocytic and intra-tick stages of the parasite, dynamic expression profiles of individual BdCDPKs were monitored, suggesting distinct roles for BdCDPKs within each host environment. In summary, this study contrasts the expression levels of individual BdCDPKs during intra-erythrocytic and intra- tick stages, providing compelling evidence for distinct regulatory pathways operating within each host. Exploring the specific functions of CDPKs in both vectors holds the potential to unveil the underlying mechanisms governing host cell invasion, intracellular parasitism, and interactions between the parasite and host. These endeavours contribute to comprehension of B. divergens parasititic strategies.

Due to the confidentiality of the unpublished data, we cannot share the poster.

Deconvolving the transcriptional signature of sexual commitment in Plasmodium falciparum schizonts

Presenter: Lauren Galloway

Authors: Lauren Galloway, Matthias Marti, Thomas Otto, Fiona Achcar, Barbara Strokes, Lauriane Sollelis

Abstract:

The Plasmodium species responsible for most of the fatal cases of malaria is Plasmodium falciparum. For successful transmission to the mosquito vector, Plasmodium must convert a subset of blood stage parasites into the only form capable of transmission: the sexual stage or gametocyte. The proportion of gametocytes produced within a given intraerythrocytic cycle is referred to as the conversion rate which is known to vary between Plasmodium species and transmission settings. During infection, the conversion rate also exhibits adaptive plasticity and is responsive to environmental factors such as depletion of the serum phospholipid lysophosphatidylcholine (LysoPC). LysoPC depletion can induce sexual commitment and stage conversion in a subset of cells in vitro, however, the transcriptional programme underlying the different parasite responses to this environmental trigger remains unclear. Here, we used single cell RNA sequencing to deconvolute the transcriptional signatures of sexually and asexually committed schizonts across two parasite strains with different LysoPC sensitivity. We validated previous findings from bulk RNA sequencing demonstrating a general metabolic response and reduced expression of nutrient channel components, such as PSAC, triggered by LysoPC depletion. We identify for the first time three major transcriptional differences between asexually and sexually committed schizonts under limiting conditions: i) induced expression of cytoadherence-linked factors such as kahrp in asexually committed schizonts (in addition to their ring stage expression peak), ii) further reduction of nutrient channel components in sexually committed schizonts, and iii) differential expression of a series of invasion ligands between asexually and sexually committed schizonts. The phenotypic relevance of these differences remains to be determined. Finally, we were able to deconvolve the pathway of sexual commitment and propose a testable model starting from the initial transcriptional response to LysoPC depletion until the positive feedback loop activating ap2-g and its downstream targets once commitment becomes irreversible.

Due to the confidentiality of the unpublished data, we cannot share the poster.

The EMBL Conference ‘BioMalPar XX: biology and pathology of the malaria parasite’ took place from 21 – 23 May 2024 at EMBL Heidelberg and virtually. To join us for the next edition, please have a look here.