Plasmodium yoelii macrophage migration inhibitory factor is necessary for efficient liver-stage development

A decade of dinoflagellate genomics illuminating an enigmatic eukaryote cell

Dinoflagellates are a remarkable group of protists, not only for their association with harmful algal blooms and coral reefs but also for their numerous characteristics deviating from the rules of eukaryotic biology. Genome research on dinoflagellates has lagged due to their immense genome sizes in most species (~ 1-250 Gbp). Nevertheless, the last decade marked a fruitful era of dinoflagellate genomics, with 27 genomes sequenced and many insights attained. This review aims to synthesize information from these genomes, along with other omic data, to reflect on where we are now in understanding dinoflagellates and where we are heading in the future. The most notable insights from the decade-long genomics work include: (1) dinoflagellate genomes have been expanded in multiple times independently, probably by a combination of rampant retroposition, accumulation of repetitive DNA, and genome duplication; (2) Symbiodiniacean genomes are highly divergent, but share about 3,445 core unigenes concentrated in 219 KEGG pathways; (3) Most dinoflagellate genes are encoded unidirectionally and are not intron-poor; (4) The dinoflagellate nucleus has undergone extreme evolutionary changes, including complete or nearly complete loss of nucleosome and histone H1, and acquisition of dinoflagellate viral nuclear protein (DVNP); (5) Major basic nuclear protein (MBNP), histone-like protein (HLP), and bacterial HU-like protein (HCc) belong to the same protein family, and MBNP can be the unifying name; (6) Dinoflagellate gene expression is regulated by poorly understood mechanisms, but microRNA and other epigenetic mechanisms are likely important; (7) Over 50% of dinoflagellate genes are "dark" and their functions remain to be deciphered using functional genetics; (8) Initial insights into the genomic basis of parasitism and mutualism have emerged. The review then highlights functionally unique and interesting genes. Future research needs to obtain a finished genome, tackle large genomes, characterize the unknown genes, and develop a quantitative molecular ecological model for addressing ecological questions.

Macrophage migration inhibitory factor favors Neospora caninum infection in mice

Neospora caninum is a protozoan parasite with worldwide incidence, acting as a major cause of reproductive failures in ruminants and neuromuscular symptoms in dogs. Macrophage Migration Inhibitory Factor (MIF) is produced by several cell types and exhibits a central role in immune responses against intracellular pathogens. The present study aimed to comprehend the role of MIF in the relationship between N. caninum and its host. We used in vivo, in vitro and ex vivo experiments in a model of infection based on genetically deficient mice to analyze the infection kinetics and inflammatory markers. MIF production was measured in response to N. caninum during the acute and chronic phases of the infection. While Mif-/- mice survived lethal doses of NcLiv tachyzoites, sublethal infections in these mice showed that parasite burden was controlled in target tissues, alongside with reduced inflammatory infiltrates detected in lung and brain sections. TNF was increased at the initial site of the infection in genetically deficient mice and the MIF-dependent reduction was confirmed in vitro with macrophages and ex vivo with primed spleen cells. In sum, MIF negatively regulated host immunity against N. caninum, favoring disease progression.

MIF-like domain containing protein orchestrates cellular differentiation and virulence in the fungal pathogen Magnaporthe oryzae

Macrophage migration inhibitory factor (MIF) is a pleiotropic protein with chemotactic, pro-inflammatory, and growth-promoting activities first discovered in mammals. In parasites, MIF homologs are involved in immune evasion and pathogenesis. Here, we present the first comprehensive analysis of an MIF protein from the devastating plant pathogen Magnaporthe oryzae (Mo). The fungal genome encodes a single MIF protein (MoMIF1) that, unlike the human homolog, harbors multiple low-complexity regions (LCRs) and is unique to Ascomycota. Following infection, MoMIF1 is expressed in the biotrophic phase of the fungus, and is strongly down-regulated during subsequent necrotrophic growth in leaves and roots. We show that MoMIF1 is secreted during plant infection, affects the production of the mycotoxin tenuazonic acid and inhibits plant cell death. Our results suggest that MoMIF1 is a novel key regulator of fungal virulence that maintains the balance between biotrophy and necrotrophy during the different phases of fungal infection.

Macrophage Migration Inhibitory Factor in Psoroptes ovis: Molecular Characterization and Potential Role in Eosinophil Accumulation of Skin in Rabbit and Its Implication in the Host-Parasite Interaction

Psoroptes ovis, a common surface-living mite of domestic and wild animals worldwide, results in huge economic losses and serious welfare issues in the animal industry. P. ovis infestation rapidly causes massive eosinophil infiltration in skin lesions, and increasing research revealed that eosinophils might play an important role in the pathogenesis of P. ovis infestation. Intradermal injection of P. ovis antigen invoked massive eosinophil infiltration, suggesting that this mite should contain some relative molecules involved in eosinophil accumulation in the skin. However, these active molecules have not yet been identified. Herein, we identified macrophage migration inhibitor factor (MIF) in P. ovis (PsoMIF) using bioinformatics and molecular biology methods. Sequence analyses revealed that PsoMIF appeared with high similarity to the topology of monomer and trimer formation with host MIF (RMSD = 0.28 angstroms and 2.826 angstroms, respectively) but with differences in tautomerase and thiol-protein oxidoreductase active sites. Reverse transcription PCR analysis (qRT-PCR) results showed that PsoMIF was expressed throughout all the developmental stages of P. ovis, particularly with the highest expression in female mites. Immunolocalization revealed that MIF protein located in the ovary and oviduct of female mites and also localized throughout the stratum spinosum, stratum granulosum, and even basal layers of the epidermis in skin lesions caused by P. ovis. rPsoMIF significantly upregulated eosinophil-related gene expression both in vitro (PBMC: CCL5, CCL11; HaCaT: IL-3, IL-4, IL-5, CCL5, CCL11) and in vivo (rabbit: IL-5, CCL5, CCL11, P-selectin, ICAM-1). Moreover, rPsoMIF could induce cutaneous eosinophil accumulation in a rabbit model and increased the vascular permeability in a mouse model. Our findings indicated that PsoMIF served as one of the key molecules contributing to skin eosinophil accumulation in P. ovis infection of rabbits.

Plasmodium-encoded murine IL-6 impairs liver stage infection and elicits long-lasting sterilizing immunity

Introduction

Plasmodium sporozoites (SPZ) inoculated by Anopheles mosquitoes into the skin of the mammalian host migrate to the liver before infecting hepatocytes. Previous work demonstrated that early production of IL-6 in the liver is detrimental for the parasite growth, contributing to the acquisition of a long-lasting immune protection after immunization with live attenuated parasites.

Methods

Considering that IL-6 as a critical pro-inflammatory signal, we explored a novel approach whereby the parasite itself encodes for the murine IL-6 gene. We generated transgenic P. berghei parasites that express murine IL-6 during liver stage development.

Results and Discussion

Though IL-6 transgenic SPZ developed into exo-erythrocytic forms in hepatocytes in vitro and in vivo, these parasites were not capable of inducing a blood stage infection in mice. Furthermore, immunization of mice with transgenic IL-6-expressing P. berghei SPZ elicited a long-lasting CD8⁺ T cell-mediated protective immunity against a subsequent infectious SPZ challenge. Collectively, this study demonstrates that parasite-encoded IL-6 attenuates parasite virulence with abortive liver stage of Plasmodium infection, forming the basis of a novel suicide vaccine strategy to elicit protective antimalarial immunity.

Detection of positive selection acting on protein surfaces at the whole-genome scale in the human malaria parasite Plasmodium falciparum

The host-parasite evolutionary arms race is a fundamental process with medical implications. During this process, the host develops parasite resistance, and the parasite develops host immune evasion strategies. Thus, this process accelerates relevant protein evolution. This study test hypothesizes that proteins subject to sequence evolution structural constraints play a crucial role and that these constraints hinder the modification of such proteins in this process. These hypotheses were tested using Plasmodium falciparum model and evaluated protein structures predicted for the entire proteome by the AlphaFold method. Based on dN/dS test results and P. falciparum and P. reichenowi comparisons, the presented approach identified proteins subject to purifying selection acting on the whole sequence and buried residues (dN < dS) and positive selection on nonburied residues. Of the 26 proteins, some known antigens (ring-exported protein 3, RAP protein, erythrocyte binding antigen-140, and protein P47) targeted by the host immune system are promising vaccine candidates. The set also contained 11 enzymes, including FIKK kinase, which modifies host proteins. This set was compared with genes for which the dN/dS test suggested that positive selection acts on the whole gene (i.e., dN > dS). The present study found that such genes encode enzymes and antigenic vaccine candidates less frequently than genes for which evolution is not subject to selection constraints and positive selection acts on only exposed residues. The analysis was repeated comparing P. falciparum with P. alderi, which is more distantly related. The study discusses the potential implications of the presented methodology for rational vaccine design and the parasitology and evolutionary biology fields.

Macrophage migration inhibitory factor contributes to immunopathogenesis during Plasmodium yoelii 17XL infection

Macrophage migration inhibitory factor (MIF) is a cytokine recognized regulator of the inflammatory immune response associated with several immune cells that produce inflammatory cytokines such as IL-1β, IL-6, IL-12, IL-18, and TNF-α. This study aimed to understand the effect of MIF on the immune response and pathogenesis during Plasmodium infection. Wild-type (Wt) and MIF knockout (Mif ^-/-) mice were intravenously infected with 1×10³ Plasmodium yoelii (Py) 17XL-parasitized red blood cells. Our data showed that Py17XL-infected Wt mice died 11 days postinfection, while Mif ^-/- mice showed reduced parasitemia and an increase in their survival at day 11 up to 58%, importantly they succumb up to day 21 postinfection. The increased survival rate in Mif ^-/- mice was associated with less severe cachexia and anemia as a result of a mixed Th1/Th2 cytokine profile, high levels of IL-12, IL-17/IL-4, and IL-10 in serum; and high levels of IL-4 and IL-10, and low levels of IFN-γ in spleen cells compared to Py17XL infected Wt mice. Moreover, macrophages (Mφs) from Mif ^-/- mice exhibited higher concentrations of IL-10 and IL-12 and reduced levels of TNF-α and nitric oxide (NO) compared to Py17XL-infected Wt mice. These results demonstrate that MIF has an important role in regulating the immune response associated with host pathogenesis and lethality, which is relevant to consider in preventing/reducing complications in Plasmodium infections.

Suppression of Plasmodium MIF-CD74 signaling protects against severe malaria

The deadliest complication of infection by Plasmodium parasites, cerebral malaria, accounts for the majority of malarial fatalities. Although our understanding of the cellular and molecular mechanisms underlying the pathology remains incomplete, recent studies support the contribution of systemic and neuroinflammation as the cause of cerebral edema and blood-brain barrier (BBB) dysfunction. All Plasmodium species encode an orthologue of the innate cytokine, Macrophage Migration Inhibitory Factor (MIF), which functions in mammalian biology to regulate innate responses. Plasmodium MIF (PMIF) similarly signals through the host MIF receptor CD74, leading to an enhanced inflammatory response. We investigated the PMIF-CD74 interaction in the onset of experimental cerebral malaria (ECM) and liver stage Plasmodium development by using a combination of CD74 deficient (Cd74^-/- ) hosts and PMIF deficient parasites. Cd74^-/- mice were found to be protected from ECM and the protection was associated with the inability of brain microvessels to present parasite antigen to sequestered and pathogenic Plasmodium-specific CD8⁺ T cells. Infection of WT hosts with PMIF-deficient sporozoites or infection of Cd74^-/- hosts with WT sporozoites impacted the survival of infected hepatocytes and subsequently reduced blood-stage associated inflammation, contributing to protection from ECM. We recapitulated these finding with a novel pharmacologic PMIF-selective antagonist that reduced PMIF/CD74 signaling and fully protected mice from ECM. These findings reveal a conserved mechanism for Plasmodium usurpation of host CD74 signaling and suggest a tractable approach for new pharmacologic intervention.

Expansion and loss events characterized the occurrence of MIF-like genes in bivalves

Macrophage migration inhibitory factor (MIF) dynamically connects innate and adaptive immune systems in vertebrate animals, allowing highly orchestrated systemic responses to various insults. The occurrence of MIF-like genes in non-vertebrate organisms suggests its origin from an ancestral metazoan gene, whose function is still a matter of debate. In the present work, by analyzing available genomic and transcriptomic data from bivalve mollusks, we identified 137 MIF-like sequences, which were classified into three types, based on phylogeny and conservation of key residues: MIF, D-DT, and the lineage-specific type MDL. Comparative genomics revealed syntenic conservation of homologous genes at the family level, the loss of D-DT in the Ostreidae family as well as the expansion of MIF-like genes in the Mytilidae family, possibly underpinning the neofunctionalization of duplicated gene copies. In M. galloprovincialis, MIF and one D-DT were mostly expressed in haemocytes and mantle rim of untreated animals, while D-DT paralogs often showed very limited expression, suggesting an accessory role or their persistence as relict genes.

Chronic TLR7 and TLR9 signaling drives anemia via differentiation of specialized hemophagocytes

Cytopenias are an important clinical problem associated with inflammatory disease and infection. We show that specialized phagocytes that internalize red blood cells develop in Toll-like receptor 7 (TLR7)-driven inflammation. TLR7 signaling caused the development of inflammatory hemophagocytes (iHPCs), which resemble splenic red pulp macrophages but are a distinct population derived from Ly6C^hi monocytes. iHPCs were responsible for anemia and thrombocytopenia in TLR7-overexpressing mice, which have a macrophage activation syndrome (MAS)-like disease. Interferon regulatory factor 5 (IRF5), associated with MAS, participated in TLR7-driven iHPC differentiation. We also found iHPCs during experimental malarial anemia, in which they required endosomal TLR and MyD88 signaling for differentiation. Our findings uncover a mechanism by which TLR7 and TLR9 specify monocyte fate and identify a specialized population of phagocytes responsible for anemia and thrombocytopenia associated with inflammation and infection.

Ribozyme-mediated, multiplex CRISPR gene editing and CRISPR interference (CRISPRi) in rodent-infectious Plasmodium yoelii

Malaria remains a major global health issue, affecting millions and killing hundreds of thousands of people annually. Efforts to break the transmission cycle of the causal Plasmodium parasite, and to cure those that are afflicted, rely upon functional characterization of genes essential to the parasite's growth and development. These studies are often based upon manipulations of the parasite genome to disrupt or modify a gene of interest to understand its importance and function. However, these approaches can be limited by the availability of selectable markers and the time required to generate transgenic parasites. Moreover, there also is a risk of disrupting native gene regulatory elements with the introduction of exogenous sequences. To address these limitations, we have developed CRISPR-RGR, a Streptococcus pyogenes (Sp)Cas9-based gene editing system for Plasmodium that utilizes a ribozyme-guide-ribozyme (RGR) single guide RNA (sgRNA) expression strategy with RNA polymerase II promoters. Using rodent-infectious Plasmodium yoelii, we demonstrate that both gene disruptions and coding sequence insertions are efficiently generated, producing marker-free parasites with homology arms as short as 80-100 bp. Additionally, we find that the common practice of using one sgRNA can produce both unintended plasmid integration and desired locus replacement editing events, whereas the use of two sgRNAs results in only locus replacement editing. Lastly, we show that CRISPR-RGR can be used for CRISPR interference (CRISPRi) by binding catalytically dead SpCas9 (dSpCas9) to the region upstream of a gene of interest, resulting in a position-dependent, but strand-independent reduction in gene expression. This robust and flexible system facilitates efficient genetic characterizations of rodent-infectious Plasmodium species.

Host-parasite interactions and ecology of the malaria parasite-a bioinformatics approach

Malaria remains one of the highest mortality infectious diseases. Malaria is caused by parasites from the genus Plasmodium. Most deaths are caused by infections involving Plasmodium falciparum, which has a complex life cycle. Malaria parasites are extremely well adapted for interactions with their host and their host's immune system and are able to suppress the human immune system, erase immunological memory and rapidly alter exposed antigens. Owing to this rapid evolution, parasites develop drug resistance and express novel forms of antigenic proteins that are not recognized by the host immune system. There is an emerging need for novel interventions, including novel drugs and vaccines. Designing novel therapies requires knowledge about host-parasite interactions, which is still limited. However, significant progress has recently been achieved in this field through the application of bioinformatics analysis of parasite genome sequences. In this review, we describe the main achievements in 'malarial' bioinformatics and provide examples of successful applications of protein sequence analysis. These examples include the prediction of protein functions based on homology and the prediction of protein surface localization via domain and motif analysis. Additionally, we describe PlasmoDB, a database that stores accumulated experimental data. This tool allows data mining of the stored information and will play an important role in the development of malaria science. Finally, we illustrate the application of bioinformatics in the development of population genetics research on malaria parasites, an approach referred to as reverse ecology.

Plasmodium male gametocyte development and transmission are critically regulated by the two putative deadenylases of the CAF1/CCR4/NOT complex

With relatively few known specific transcription factors to control the abundance of specific mRNAs, Plasmodium parasites may rely more on the regulation of transcript stability and turnover to provide sufficient gene regulation. Plasmodium transmission stages impose translational repression on specific transcripts in part to accomplish this. However, few proteins are known to participate in this process, and those that are characterized primarily affect female gametocytes. We have identified and characterized Plasmodium yoelii (Py) CCR4-1, a putative deadenylase, which plays a role in the development and activation of male gametocytes, regulates the abundance of specific mRNAs in gametocytes, and ultimately increases the efficiency of host-to-vector transmission. We find that when pyccr4-1 is deleted or its protein made catalytically inactive, there is a loss in the initial coordination of male gametocyte maturation and a reduction of parasite infectivity of the mosquito. Expression of only the N-terminal CAF1 domain of the essential CAF1 deadenylase leads to a similar phenotype. Comparative RNA-seq revealed that PyCCR4-1 affects transcripts important for transmission-related functions that are associated with male or female gametocytes, some of which directly associate with the immunoprecipitated complex. Finally, circular RT-PCR of one of the bound, dysregulated transcripts showed that deletion of the pyccr4-1 gene does not result in gross changes to its UTR or poly(A) tail length. We conclude that the two putative deadenylases of the CAF1/CCR4/NOT complex play critical and intertwined roles in gametocyte maturation and transmission.

Neutralization of the Plasmodium-encoded MIF ortholog confers protective immunity against malaria infection

Plasmodium species produce an ortholog of the cytokine macrophage migration inhibitory factor, PMIF, which modulates the host inflammatory response to malaria. Using a novel RNA replicon-based vaccine, we show the impact of PMIF immunoneutralization on the host response and observed improved control of liver and blood-stage Plasmodium infection, and complete protection from re-infection. Vaccination against PMIF delayed blood-stage patency after sporozoite infection, reduced the expression of the Th1-associated inflammatory markers TNF-α, IL-12, and IFN-γ during blood-stage infection, augmented Tfh cell and germinal center responses, increased anti-Plasmodium antibody titers, and enhanced the differentiation of antigen-experienced memory CD4 T cells and liver-resident CD8 T cells. Protection from re-infection was recapitulated by the adoptive transfer of CD8 or CD4 T cells from PMIF RNA immunized hosts. Parasite MIF inhibition may be a useful approach to promote immunity to Plasmodium and potentially other parasite genera that produce MIF orthologous proteins.

Plasmodium species produce an ortholog of the cytokine macrophage migration inhibitory factor, PMIF, which modulates the host inflammatory response to malaria. Here, the authors show that inhibition of PMIF may have translational benefits for managing malaria infections.

In Vitro Culture, Drug Sensitivity, and Transcriptome of Plasmodium Vivax Hypnozoites

The unique relapsing nature of Plasmodium vivax infection is a major barrier to malaria eradication. Upon infection, dormant liver-stage forms, hypnozoites, linger for weeks to months and then relapse to cause recurrent blood-stage infection. Very little is known about hypnozoite biology; definitive biomarkers are lacking and in vitro platforms that support phenotypic studies are needed. Here, we recapitulate the entire liver stage of P. vivax in vitro, using a multiwell format that incorporates micropatterned primary human hepatocyte co-cultures (MPCCs). MPCCs feature key aspects of P. vivax biology, including establishment of persistent small forms and growing schizonts, merosome release, and subsequent infection of reticulocytes. We find that the small forms exhibit previously described hallmarks of hypnozoites, and we pilot MPCCs as a tool for testing candidate anti-hypnozoite drugs. Finally, we employ a hybrid capture strategy and RNA sequencing to describe the hypnozoite transcriptome and gain insight into its biology.

Nuclear, Cytosolic, and Surface-Localized Poly(A)-Binding Proteins of Plasmodium yoelii

Malaria remains one of the great global health problems. The parasite that causes malaria (Plasmodium genus) relies upon exquisite control of its transmission between vertebrate hosts and mosquitoes. One crucial way that it does so is by proactively producing mRNAs needed to establish the new infection but by silencing and storing them until they are needed. One key protein in this process of translational repression in model eukaryotes is poly(A)-binding protein (PABP). Here we have shown that Plasmodium yoelii utilizes both a nuclear PABP and a cytosolic PABP, both of which bind specifically to polyadenylated RNA sequences. Moreover, we find that the cytosolic PABP forms chains in vitro, consistent with its appreciated role in coating the poly(A) tails of mRNA. Finally, we have also verified that, surprisingly, the cytosolic PABP is found on the surface of Plasmodium sporozoites. Taking the data together, we propose that Plasmodium utilizes a more metazoan-like strategy for RNA metabolism using specialized PABPs.

Malaria is a devastating illness that causes approximately 500,000 deaths annually. The malaria-causing parasite (Plasmodium genus) uses the process of translational repression to regulate its growth, development, and transmission. As poly(A)-binding proteins (PABP) have been identified as critical components of RNA metabolism and translational repression in model eukaryotes and in Plasmodium, we have identified and investigated two PABPs in Plasmodium yoelii, PyPABP1 and PyPABP2. In contrast to most single-celled eukaryotes, Plasmodium closely resembles metazoans and encodes both a nuclear PABP and a cytosolic PABP; here, we provide multiple lines of evidence in support of this observation. The conserved domain architectures of PyPABP1 and PyPABP2 resemble those of yeast and metazoans, while multiple independent binding assays demonstrated their ability to bind very strongly and specifically to poly(A) sequences. Interestingly, we also observed that purified PyPABP1 forms homopolymeric chains despite exhaustive RNase treatment in vitro. Finally, we show by indirect immunofluorescence assays (IFAs) that PyPABP1 and PyPABP2 are cytoplasm- and nucleus-associated PABPs during the blood stages of the life cycle. Surprisingly, however, PyPABP1 was instead observed to also be localized on the surface of transmitted salivary gland sporozoites and to be deposited in trails when parasites glide on a substrate. This is the third RNA-binding protein verified to be found on the sporozoite surface, and the data may point to an unappreciated RNA-centered interface between the host and parasite.

IMPORTANCE Malaria remains one of the great global health problems. The parasite that causes malaria (Plasmodium genus) relies upon exquisite control of its transmission between vertebrate hosts and mosquitoes. One crucial way that it does so is by proactively producing mRNAs needed to establish the new infection but by silencing and storing them until they are needed. One key protein in this process of translational repression in model eukaryotes is poly(A)-binding protein (PABP). Here we have shown that Plasmodium yoelii utilizes both a nuclear PABP and a cytosolic PABP, both of which bind specifically to polyadenylated RNA sequences. Moreover, we find that the cytosolic PABP forms chains in vitro, consistent with its appreciated role in coating the poly(A) tails of mRNA. Finally, we have also verified that, surprisingly, the cytosolic PABP is found on the surface of Plasmodium sporozoites. Taking the data together, we propose that Plasmodium utilizes a more metazoan-like strategy for RNA metabolism using specialized PABPs.

Dietary alterations modulate susceptibility to Plasmodium infection

The relevance of genetic factors in conferring protection to severe malaria has been demonstrated, as in the case of sickle cell trait and G6PD deficiency ¹ . However, it remains unknown whether environmental components, such as dietary or metabolic variations, can contribute to the outcome of infection ² . Here, we show that administration of a high-fat diet to mice for a period as short as 4 days impairs Plasmodium liver infection by over 90%. Plasmodium sporozoites can successfully invade and initiate replication but die inside hepatocytes, thereby are unable to cause severe disease. Transcriptional analyses combined with genetic and chemical approaches reveal that this impairment of infection is mediated by oxidative stress. We show that reactive oxygen species, probably spawned from fatty acid β-oxidation, directly impact Plasmodium survival inside hepatocytes, and parasite load can be rescued by exogenous administration of the antioxidant N-acetylcysteine or the β-oxidation inhibitor etomoxir. Together, these data reveal that acute and transient dietary alterations markedly impact the establishment of a Plasmodium infection and disease outcome.

ALBA4 modulates its stage-specific interactions and specific mRNA fates during Plasmodium yoelii growth and transmission

Transmission of the malaria parasite occurs in an unpredictable moment, when a mosquito takes a blood meal. Plasmodium has therefore evolved strategies to prepare for transmission, including translationally repressing and protecting mRNAs needed to establish the infection. However, mechanisms underlying these critical controls are not well understood, including whether Plasmodium changes its translationally repressive complexes and mRNA targets in different stages. Efforts to understand this have been stymied by severe technical limitations due to substantial mosquito contamination of samples. Here using P. yoelii, for the first time we provide a proteomic comparison of a protein complex across asexual blood, sexual and sporozoite stages, along with a transcriptomic comparison of the mRNAs that are affected in these stages. We find that the Apicomplexan-specific ALBA4 RNA-binding protein acts to regulate development of the parasite's transmission stages, and that ALBA4 associates with both stage-specific and stage-independent partners to produce opposing mRNA fates. These efforts expand our understanding and ability to interrogate both sexual and sporozoite transmission stages and the molecular preparations they evolved to perpetuate their infectious cycle.

Malaria Parasite Liver Infection and Exoerythrocytic Biology

In their infection cycle, malaria parasites undergo replication and population expansions within the vertebrate host and the mosquito vector. Host infection initiates with sporozoite invasion of hepatocytes, followed by a dramatic parasite amplification event during liver stage parasite growth and replication within hepatocytes. Each liver stage forms up to 90,000 exoerythrocytic merozoites, which are in turn capable of initiating a blood stage infection. Liver stages not only exploit host hepatocyte resources for nutritional needs but also endeavor to prevent hepatocyte cell death and detection by the host's immune system. Research over the past decade has identified numerous parasite factors that play a critical role during liver infection and has started to delineate a complex web of parasite-host interactions that sustain successful parasite colonization of the mammalian host. Targeting the parasites' obligatory infection of the liver as a gateway to the blood, with drugs and vaccines, constitutes the most effective strategy for malaria eradication, as it would prevent clinical disease and onward transmission of the parasite.

Reprint of: The non-mammalian MIF superfamily

Macrophage migration inhibitory factor (MIF) was first described as a cytokine 50 years ago, and emerged in mammals as a pleiotropic protein with pro-inflammatory, chemotactic, and growth-promoting activities. In addition, MIF has gained substantial attention as a pivotal upstream mediator of innate and adaptive immune responses and with pathologic roles in several diseases. Of less importance in mammals is an intrinsic but non-physiologic enzymatic activity that points to MIF's evolution from an ancient defense molecule. Therefore, it is not surprising that mif-like genes also have been found across a range of different organisms including bacteria, plants, protozoa, helminths, molluscs, arthropods, fish, amphibians and birds. While Genebank analysis identifying mif-like genes across species is extensive, contained herein is an overview of the non-mammalian MIF-like proteins that have been most well studied experimentally. For many of these organisms, MIF contributes to an innate defense system or plays a role in development. For parasitic organisms however, MIF appears to function as a virulence factor aiding in the establishment or persistence of infection by modulating the host immune response. Consequently, a combined targeting of both parasitic and host MIF could lead to more effective treatment strategies for parasitic diseases of socioeconomic importance.

Host-Parasite Interactions in Human Malaria: Clinical Implications of Basic Research

The malaria parasite, Plasmodium, is one of the oldest parasites documented to infect humans and has proven particularly hard to eradicate. One of the major hurdles in designing an effective subunit vaccine against the malaria parasite is the insufficient understanding of host–parasite interactions within the human host during infections. The success of the parasite lies in its ability to evade the human immune system and recruit host responses as physiological cues to regulate its life cycle, leading to rapid acclimatization of the parasite to its immediate host environment. Hence understanding the environmental niche of the parasite is crucial in developing strategies to combat this deadly infectious disease. It has been increasingly recognized that interactions between parasite proteins and host factors are essential to establishing infection and virulence at every stage of the parasite life cycle. This review reassesses all of these interactions and discusses their clinical importance in designing therapeutic approaches such as design of novel vaccines. The interactions have been followed from the initial stages of introduction of the parasite under the human dermis until asexual and sexual blood stages which are essential for transmission of malaria. We further classify the interactions as “direct” or “indirect” depending upon their demonstrated ability to mediate direct physical interactions of the parasite with host factors or their indirect manipulation of the host immune system since both forms of interactions are known to have a crucial role during infections. We also discuss the many ways in which this understanding has been taken to the field and the success of these strategies in controlling human malaria.

Towards a Humanized Mouse Model of Liver Stage Malaria Using Ectopic Artificial Livers

The malaria liver stage is an attractive target for antimalarial development, and preclinical malaria models are essential for testing such candidates. Given ethical concerns and costs associated with non-human primate models, humanized mouse models containing chimeric human livers offer a valuable alternative as small animal models of liver stage human malaria. The best available human liver chimeric mice rely on cellular transplantation into mice with genetically engineered liver injury, but these systems involve a long and variable humanization process, are expensive, and require the use of breeding-challenged mouse strains which are not widely accessible. We previously incorporated primary human hepatocytes into engineered polyethylene glycol (PEG)-based nanoporous human ectopic artificial livers (HEALs), implanted them in mice without liver injury, and rapidly generated human liver chimeric mice in a reproducible and scalable fashion. By re-designing the PEG scaffold to be macroporous, we demonstrate the facile fabrication of implantable porous HEALs that support liver stage human malaria (P. falciparum) infection in vitro, and also after implantation in mice with normal liver function, 60% of the time. This proof-of-concept study demonstrates the feasibility of applying a tissue engineering strategy towards the development of scalable preclinical models of liver stage malaria infection for future applications.

PyMIF enhances the inflammatory response in a rodent model by stimulating CD11b(+) Ly6C(+) cells accumulation in spleen

Macrophage migration inhibitory factor (PMIF) expressed by Plasmodium parasites has been proved to be similar to the mammalian MIF in both structure and biological activity and is a critical upstream regulator in antimalaria innate immunity. In this work, using a genetically modified (MIF-KO) strain of highly lethal rodent Plasmodium yoelii 17XL (Py17XL), we found that PyMIF could increase the secretion of pro-inflammatory factors by eliciting the CD11b(+) Ly6C(+) cells accumulated in the spleen of infected mouse. In addition, the chemotactic effect of PyMIF was demonstrated to associate with cell receptors CXCR2, CXCR4 and the cell surface markers ICAM-1, LFA-4.

The non-mammalian MIF superfamily

Macrophage migration inhibitory factor (MIF) was first described as a cytokine 50 years ago, and emerged in mammals as a pleiotropic protein with pro-inflammatory, chemotactic, and growth-promoting activities. In addition, MIF has gained substantial attention as a pivotal upstream mediator of innate and adaptive immune responses and with pathologic roles in several diseases. Of less importance in mammals is an intrinsic but non-physiologic enzymatic activity that points to MIF's evolution from an ancient defense molecule. Therefore, it is not surprising that mif-like genes also have been found across a range of different organisms including bacteria, plants, ‎protozoa, helminths, molluscs, arthropods, fish, amphibians and birds. While Genebank analysis identifying mif-like genes across species is extensive, contained herein is an overview of the non-mammalian MIF-like proteins that have been most well studied experimentally. For many of these organisms, MIF contributes to an innate defense system or plays a role in development. For parasitic organisms however, MIF appears to function as a virulence factor aiding in the establishment or persistence of infection by modulating the host immune response. Consequently, a combined targeting of both parasitic and host MIF could lead to more effective treatment strategies for parasitic diseases of socioeconomic importance.

Time for Genome Editing: Next-Generation Attenuated Malaria Parasites

Immunization with malaria parasites that developmentally arrest in or immediately after the liver stage is the only way currently known to confer sterilizing immunity in both humans and rodent models. There are various ways to attenuate parasite development resulting in different timings of arrest, which has a significant impact on vaccination efficiency. To understand what most impacts vaccination efficiency, newly developed gain-of-function methods can now be used to generate a wide array of differently attenuated parasites. The combination of multiple attenuation approaches offers the potential to engineer efficiently attenuated Plasmodium parasites and learn about their fascinating biology at the same time. Here we discuss recent studies and the potential of targeted parasite manipulation using genome editing to develop live attenuated malaria vaccines.

Identification of Novel Pre-Erythrocytic Malaria Antigen Candidates for Combination Vaccines with Circumsporozoite Protein

Malaria vaccine development has been hampered by the limited availability of antigens identified through conventional discovery approaches, and improvements are needed to enhance the efficacy of the leading vaccine candidate RTS,S that targets the circumsporozoite protein (CSP) of the infective sporozoite. Here we report a transcriptome-based approach to identify novel pre-erythrocytic vaccine antigens that could potentially be used in combination with CSP. We hypothesized that stage-specific upregulated genes would enrich for protective vaccine targets, and used tiling microarray to identify P. falciparum genes transcribed at higher levels during liver stage versus sporozoite or blood stages of development. We prepared DNA vaccines for 21 genes using the predicted orthologues in P. yoelii and P. berghei and tested their efficacy using different delivery methods against pre-erythrocytic malaria in rodent models. In our primary screen using P. yoelii in BALB/c mice, we found that 16 antigens significantly reduced liver stage parasite burden. In our confirmatory screen using P. berghei in C57Bl/6 mice, we confirmed 6 antigens that were protective in both models. Two antigens, when combined with CSP, provided significantly greater protection than CSP alone in both models. Based on the observations reported here, transcriptional patterns of Plasmodium genes can be useful in identifying novel pre-erythrocytic antigens that induce protective immunity alone or in combination with CSP.

Proteomic characterization of mucosal secretions in the eastern oyster, Crassostrea virginica

The soft body surface of marine invertebrates is covered by a layer of mucus, a slippery gel secreted by mucocytes lining epithelia. The functions of this gel are diverse including locomotion, cleansing, food particles processing and defense against physicochemical injuries and infectious agents. In oysters, mucus covering pallial organs has been demonstrated to have a major importance in the processing of food particles and in the interactions with waterborne pathogens. Given the limited information available on mucus in bivalves and the apparent wide spectra of activity of bioactive molecules present in this matrix, the characterization of these mucosal secretions has become a research priority. In this study, mucus was separately collected from the mantle, gills and labial palps of the eastern oyster (Crassostrea virginica) and analyzed by liquid chromatography and tandem mass spectrometry. Results showed the presence of a wide variety of molecules involved in host-microbe interactions, including putative adhesion molecules (e.g. c-type lectins) confirming that transcripts previously identified in epithelial cells are translated into proteins secreted in mucus. Mucus composition was different among samples collected from different organs. These results generate a reference map for C. virginica pallial mucus to better characterize the various physiological functions of mucosal secretions.

Chimeric DNA vaccines encoding Eimeria acervulina macrophage migration inhibitory factor (E.MIF) induce partial protection against experimental Eimeria infection

Chimeric DNA vaccines co-expressing Eimeria acervulina macrophage migration inhibitory factor (E.MIF) and chicken IL-2 (IL-2) or interferon-γ (IFN-γ) were constructed and their efficacies against E. acervulina were evaluated. The open reading frame (ORF) of E.MIF was cloned from E. acervulina merozoites and subcloned into the eukaryotic expression vector pVAX1 with chicken cytokine gene IFN-γ or IL-2 to construct the DNA vaccines pVAX-E.MIF-IFN-γ, pVAX-E.MIF-IL-2 and pVAX-E.MIF. The in vivo transfection of the target genes was detected by use of reverse transcription polymerase chain reaction (RT-PCR) and Western blot. Immunizations were carried out by vaccinating chickens twice with a dose rate of 100 μg intramuscularly. Seven days post second immunization, all chickens except the unchallenged control group were challenged orally with 1 × 105 sporulated oocysts of E. acervulina. Seven days later, the duodenum was collected. The results showed that the target genes were expressed effectively in vivo. DNA vaccines and the recombinant E.MIF protein could alleviate body weight loss and duodenal lesions significantly compared to the control groups. Furthermore, pVAX-E.MIF-IL-2 and pVAX-E.MIF-IFN-γ induced anticoccidial indexs (ACIs) of 179.12 and 170, respectively, which were significantly higher than that of pVAX-E.MIF (ACI = 162.31). Our results demonstrated that E.MIF is a potential vaccine candidate against E. acervulina and chicken IFN-γ or IL- 2 may be used as genetic adjuvants to improve the efficacies of DNA vaccines against avian coccidiosis.

A Plasmodium α/β-hydrolase modulates the development of invasive stages

The bud emergence (BEM)46 proteins are evolutionarily conserved members of the α/β-hydrolase superfamily, which includes enzymes with diverse functions and a wide range of substrates. Here, we identified a Plasmodium BEM46-like protein (PBLP) and characterized it throughout the life cycle of the rodent malaria parasite Plasmodium yoelii. The Plasmodium BEM46-like protein is shown to be closely associated with the parasite plasma membrane of asexual erythrocytic stage schizonts and exo-erythrocytic schizonts; however, PBLP localizes to unique intracellular structures in sporozoites. Generation and analysis of P. yoelii knockout (Δpblp) parasite lines showed that PBLP has an important role in erythrocytic stage merozoite development with Δpblp parasites forming fewer merozoites during schizogony, which results in decreased parasitemia when compared with wild-type (WT) parasites. Δpblp parasites showed no defects in gametogenesis or transmission to mosquitoes; however, because they formed fewer oocysts there was a reduction in the number of developed sporozoites in infected mosquitoes when compared with WT. Although Δpblp sporozoites showed no apparent defect in mosquito salivary gland infection, they showed decreased infectivity in hepatocytes in vitro. Similarly, mice infected with Δpblp sporozoites exhibited a delay in the onset of blood-stage patency, which is likely caused by reduced sporozoite infectivity and a discernible delay in exo-erythrocytic merozoite formation. These data are consistent with the model that PBLP has an important role in parasite invasive-stage morphogenesis throughout the parasite life cycle.

The innate and adaptive response to mosquito saliva and Plasmodium sporozoites in the skin

A malaria infection begins when an infected mosquito takes a blood meal and inoculates parasites into the skin of its mammalian host. The parasite then has to exit the skin and escape the immune cells that protect the body from infection and alert the system to intruding pathogens. It has become apparent that this earliest stage of infection is amenable to vaccine interventions. Here, we discuss how the innate and adaptive host response to both mosquito saliva and the parasite may interfere with the infection, as well as possible mechanisms the parasite might use to circumvent the host defense.

Plasmodium vivax liver stage development and hypnozoite persistence in human liver-chimeric mice

Plasmodium vivax malaria is characterized by periodic relapses of symptomatic blood stage parasite infections likely initiated by activation of dormant liver stage parasites-hypnozoites. The lack of tractable P. vivax animal models constitutes an obstacle in examining P. vivax liver stage infection and drug efficacy. To overcome this obstacle, we have used human liver-chimeric (huHep) FRG KO mice as a model for P. vivax infection. FRG KO huHep mice support P. vivax sporozoite infection, liver stage development, and hypnozoite formation. We show complete P. vivax liver stage development, including maturation into infectious exo-erythrocytic merozoites as well as the formation and persistence of hypnozoites. Prophylaxis or treatment with the antimalarial primaquine can prevent and eliminate liver stage infection, respectively. Thus, P. vivax-infected FRG KO huHep mice are a model to investigate liver stage development and dormancy and may facilitate the discovery of drugs targeting relapsing malaria.

Susceptibility to Plasmodium yoelii preerythrocytic infection in BALB/c substrains is determined at the point of hepatocyte invasion

After transmission by Anopheles mosquitoes, Plasmodium sporozoites travel to the liver, infect hepatocytes, and rapidly develop as intrahepatocytic liver stages (LS). Rodent models of malaria exhibit large differences in the magnitude of liver infection, both between parasite species and between strains of mice. This has been mainly attributed to differences in innate immune responses and parasite infectivity. Here, we report that BALB/cByJ mice are more susceptible to Plasmodium yoelii preerythrocytic infection than BALB/cJ mice. This difference occurs at the level of early hepatocyte infection, but expression levels of reported host factors that are involved in infection do not correlate with susceptibility. Interestingly, BALB/cByJ hepatocytes are more frequently polyploid; thus, their susceptibility converges on the previously observed preference of sporozoites to infect polyploid hepatocytes. Gene expression analysis demonstrates hepatocyte-specific differences in mRNA abundance for numerous genes between BALB/cByJ and BALB/cJ mice, some of which encode hepatocyte surface molecules. These data suggest that a yet-unknown receptor for sporozoite infection, present at elevated levels on BALB/cByJ hepatocytes and also polyploid hepatocytes, might facilitate Plasmodium liver infection.

The macrophage migration inhibitory factor homolog of Entamoeba histolytica binds to and immunomodulates host macrophages

The host inflammatory response contributes to the tissue damage that occurs during amebic colitis, with tumor necrosis factor alpha (TNF-α) being a key mediator of the gut inflammation observed. Mammalian macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that plays an important role in the exacerbation of a wide range of inflammatory diseases, including colitis. We identified a MIF gene homolog in the Entamoeba histolytica genome, raising the question of whether E. histolytica MIF (EhMIF) has proinflammatory activity similar to that of mammalian MIF. In this report, we describe the first functional characterization of EhMIF. Antibodies were prepared against recombinantly expressed EhMIF and used to demonstrate that EhMIF is expressed as a 12-kDa protein localized to the cytoplasm of trophozoites. In a manner similar to that of mammalian MIF, EhMIF interacted with the MIF receptor CD74 and bound to macrophages. EhMIF induced interleukin-6 (IL-6) production. In addition, EhMIF enhanced TNF-α secretion by amplifying TNF-α production by lipopolysaccharide (LPS)-stimulated macrophages and by inhibiting the glucocorticoid-mediated suppression of TNF-α secretion. EhMIF was expressed during human infection, as evidenced by the presence of anti-EhMIF antibodies in the sera of children living in an area where E. histolytica infection is endemic. Anti-EhMIF antibodies did not cross-react with human MIF. The ability of EhMIF to modulate host macrophage function may promote an exaggerated proinflammatory immune response and contribute to the tissue damage seen in amebic colitis.

Characterization of Neospora caninum macrophage migration inhibitory factor

The present study is the first characterization of Neospora caninum macrophage migration inhibitory factor (NcMIF). BLAST-N analysis of NcMIF revealed high similarity (87%) to the Toxoplasma gondii MIF. NcMIF was cloned and expressed in Escherichia coli in 3 forms, NcMIF (mature protein), NcMIFm (mutation of proline-2 to glycine), and NcMIFhis (addition of a polyhistidine tag at the N-terminus). None of these recombinant NcMIFs (rNcMIF) had tautomerase, oxidoreductase, or immunologic regulatory activities. rNcMIF was unable to compete with recombinant human MIF for a MIF receptor (CD74), suggesting that NcMIF does not bind to this MIF receptor. The glycine substitution for proline-2 of NcMIF resulted in increased retention time on SEC-HPLC and decreased formation of dimers and trimers. The addition of N-terminal HIS-tag led to increased formation of trimers. Immunofluorescence staining demonstrated that NcMIF was localized to the apical end of N. caninum tachyzoites. Immunoelectron microscopy further revealed that NcMIF was present in the micronemes, rhoptries, dense granules, and nuclei. NcMIF was abundant in the tachyzoite lysate and present in excretory and secretory antigen (ESAg) preparations. Total and secretory NcMIF was more abundant in a non-pathologic clone, Ncts-8, than in the wild type isolate (NC1). Furthermore, NcMIF release by the both isolates was increased in the presence of calcium ionophore. This differential production of NcMIF by the pathologic and non-pathologic isolates of N. caninum may suggest a critical role of this molecule in the infectious pathogenesis of this parasite.

Pre-erythrocytic malaria vaccines: identifying the targets

Pre-erythrocytic malaria vaccines target Plasmodium during its sporozoite and liver stages, and can prevent progression to blood-stage disease, which causes a million deaths each year. Whole organism sporozoite vaccines induce sterile immunity in animals and humans and guide subunit vaccine development. A recombinant protein-in-adjuvant pre-erythrocytic vaccine called RTS,S reduces clinical malaria without preventing infection in field studies and additional antigens may be required to achieve sterile immunity. Although few vaccine antigens have progressed to human testing, new insights into parasite biology, expression profiles and immunobiology have offered new targets for intervention. Future advances require human trials of additional antigens, as well as platforms to induce the durable antibody and cellular responses including CD8(+) T cells that contribute to sterile protection.

Perturbations of Plasmodium Puf2 expression and RNA-seq of Puf2-deficient sporozoites reveal a critical role in maintaining RNA homeostasis and parasite transmissibility

Malaria's cycle of infection requires parasite transmission between a mosquito vector and a mammalian host. We here demonstrate that the Plasmodium yoelii Pumilio-FBF family member Puf2 allows the sporozoite to remain infectious in the mosquito salivary glands while awaiting transmission. Puf2 mediates this solely through its RNA-binding domain (RBD) likely by stabilizing or hastening the degradation of specific mRNAs. Puf2 traffics to sporozoite cytosolic granules, which are negative for several markers of stress granules and P-bodies, and disappear rapidly after infection of hepatocytes. In contrast to previously described Plasmodium berghei pbpuf2(-) parasites, pypuf2(-) sporozoites have no apparent defect in host infection when tested early in salivary gland residence, but become progressively non-infectious and prematurely transform into EEFs during prolonged salivary gland residence. The premature overexpression of Puf2 in oocysts causes striking deregulation of sporozoite maturation and infectivity while extension of Puf2 expression in liverstages causes no defect, suggesting that the presence of Puf2 alone is not sufficient for its functions. Finally, by conducting the first comparative RNA-seq analysis of Plasmodium sporozoites, we find that Puf2 may play a role in directly or indirectly maintaining the homeostasis of specific transcripts. These findings uncover requirements for maintaining a window of opportunity for the malaria parasite to accommodate the unpredictable moment of transmission from mosquito to mammalian host.

Getting the most out of parasitic helminth transcriptomes using HelmDB: implications for biology and biotechnology

Compounded by a massive global food shortage, many parasitic diseases have a devastating, long-term impact on animal and human health and welfare worldwide. Parasitic helminths (worms) affect the health of billions of animals. Unlocking the systems biology of these neglected pathogens will underpin the design of new and improved interventions against them. Currently, the functional annotation of genomic and transcriptomic sequence data for socio-economically important parasitic worms relies almost exclusively on comparative bioinformatic analyses using model organism- and other databases. However, many genes and gene products of parasitic helminths (often >50%) cannot be annotated using this approach, because they are specific to parasites and/or do not have identifiable homologs in other organisms for which sequence data are available. This inability to fully annotate transcriptomes and predicted proteomes is a major challenge and constrains our understanding of the biology of parasites, interactions with their hosts and of parasitism and the pathogenesis of disease on a molecular level. In the present article, we compiled transcriptomic data sets of key, socioeconomically important parasitic helminths, and constructed and validated a curated database, called HelmDB (www.helmdb.org). We demonstrate how this database can be used effectively for the improvement of functional annotation by employing data integration and clustering. Importantly, HelmDB provides a practical and user-friendly toolkit for sequence browsing and comparative analyses among divergent helminth groups (including nematodes and trematodes), and should be readily adaptable and applicable to a wide range of other organisms. This web-based, integrative database should assist 'systems biology' studies of parasitic helminths, and the discovery and prioritization of novel drug and vaccine targets. This focus provides a pathway toward developing new and improved approaches for the treatment and control of parasitic diseases, with the potential for important biotechnological outcomes.

A rapid and scalable density gradient purification method for Plasmodium sporozoites

Background

Malaria remains a major human health problem, with no licensed vaccine currently available. Malaria infections initiate when infectious Plasmodium sporozoites are transmitted by Anopheline mosquitoes during their blood meal. Investigations of the malaria sporozoite are, therefore, of clear medical importance. However, sporozoites can only be produced in and isolated from mosquitoes, and their isolation results in large amounts of accompanying mosquito debris and contaminating microbes.

Methods

Here is described a discontinuous density gradient purification method for Plasmodium sporozoites that maintains parasite infectivity in vitro and in vivo and greatly reduces mosquito and microbial contaminants.

Results

This method provides clear advantages over previous approaches: it is rapid, requires no serum components, and can be scaled to purify >10⁷ sporozoites with minimal operator involvement. Moreover, it can be effectively applied to both human (Plasmodium falciparum, Plasmodium vivax) and rodent (Plasmodium yoelii) infective species with excellent recovery rates.

Conclusions

This novel method effectively purifies viable malaria sporozoites by greatly reducing contaminating mosquito debris and microbial burdens associated with parasite isolation. Large-scale preparations of purified sporozoites will allow for enhanced in vitro infections, proteomics, and biochemical characterizations. In conjunction with aseptic mosquito rearing techniques, this purification technique will also support production of live attenuated sporozoites for vaccination.

A Plasmodium-encoded cytokine suppresses T-cell immunity during malaria

The inability to acquire protective immunity against Plasmodia is the chief obstacle to malaria control, and inadequate T-cell responses may facilitate persistent blood-stage infection. Malaria is characterized by a highly inflammatory cytokine milieu, and the lack of effective protection against infection suggests that memory T cells are not adequately formed or maintained. Using a genetically targeted strain of Plasmodium berghei, we observed that the Plasmodium ortholog of macrophage migration inhibitory factor enhanced inflammatory cytokine production and also induced antigen-experienced CD4 T cells to develop into short-lived effector cells rather than memory precursor cells. The short-lived effector CD4 T cells were more susceptible to Bcl-2-associated apoptosis, resulting in decreased CD4 T-cell recall responses against challenge infections. These findings indicate that Plasmodia actively interfere with the development of immunological memory and may account for the evolutionary conservation of parasite macrophage migration inhibitory factor orthologs.