Wide host range and strong lytic activity of Staphylococcus aureus lytic phage Stau2

In searching for an alternative antibacterial agent against multidrug-resistant Staphylococcus aureus, we have isolated and characterized a lytic staphylophage, Stau2. It possesses a double-stranded DNA genome estimated to be about 134.5 kb and a morphology resembling that of members of the family Myoviridae. With an estimated latency period of 25 min and a burst size of 100 PFU/infected cell, propagation of Stau2 in liquid culture gave a lysate of ca. 6 × 10(10) PFU/ml. It was stable at pH 5 to 13 in normal saline at room temperature for at least 4 weeks and at -85°C for more than 2 years, while 1 × 10(9) out of 2 × 10(12) PFU/ml retained infectivity after 36 months at 4°C. Stau2 could lyse 80% of the S. aureus isolates (164/205) obtained from hospitals in Taiwan, with complete lysis of most of the isolates tested within 3 h; however, it was an S. aureus-specific phage because no lytic infection could be found in the coagulase-negative staphylococci tested. Its host range among S. aureus isolates was wider than that of polyvalent phage K (47%), which can also lyse many other staphylococcal species. Experiments with mice demonstrated that Stau2 could provide 100% protection from lethal infection when a multiplicity of infection of 10 was administered immediately after a challenge with S. aureus S23. Considering these results, Stau2 could be considered at least as a candidate for topical phage therapy or an additive in the food industry.     

Isolation and preliminary characterization of lytic and lysogenic phages with wide host range within the streptomycetes

Examination of approximately 700 soil samples yielded about 100 actinophages. Restriction analysis of phage DNA indicated that 57 are unique, and of these, 20 produce turbid plaques on one or more of the streptomycetes tested. Five phages are shown to insert into the genome of Streptomyces avermitilis. None of the phages was able to perform generalized transduction of S. avermitilis.     

Bacteriophages drive strain diversification in a marine Flavobacterium: implications for phage resistance and physiological properties

Genetic, structural and physiological differences between strains of the marine bacterium Cellulophaga baltica MM#3 (Flavobacteriaceae) developing in response to the activity of two virulent bacteriophages, ΦS_M and ΦS_T, was investigated during 3 weeks incubation in chemostat cultures. A distinct strain succession towards increased phage resistance and a diversification of the metabolic properties was observed. During the incubation the bacterial population diversified from a single strain, which was sensitive to 24 tested Cellulophaga phages, into a multistrain and multiresistant population, where the dominant strains had lost susceptibility to up to 22 of the tested phages. By the end of the experiment the cultures reached a quasi steady state dominated by ΦS_T‐resistant and ΦS_M + ΦS_T‐resistant strains coexisting with small populations of phage‐sensitive strains sustaining both phages at densities of > 10⁶ plaque forming units (pfu) ml^?1. Loss of susceptibility to phage infection was associated with a reduction in the strains' ability to metabolize various carbon sources as demonstrated by BIOLOG assays. This suggested a cost of resistance in terms of reduced physiological capacity. However, there was no direct correlation between the degree of resistance and the loss of metabolic properties, suggesting either the occurrence of compensatory mutations in successful strains or that the cost of resistance in some strains was associated with properties not resolved by the BIOLOG assay. The study represents the first direct demonstration of phage‐driven generation of functional diversity within a marine bacterial host population with significant implications for both phage susceptibility and physiological properties. We propose, therefore, that phage‐mediated selection for resistant strains contributes significantly to the extensive microdiversity observed within specific bacterial species in marine environments.     

Molecular interactions between bacterial symbionts and their hosts

Symbiotic bacteria are important in animal hosts, but have been largely overlooked as they have proved difficult to culture in the laboratory. Approaches such as comparative genomics and real-time PCR have provided insights into the molecular mechanisms that underpin symbiont-host interactions. Studies on the heritable symbionts of insects have yielded valuable information about how bacteria infect host cells, avoid immune responses, and manipulate host physiology. Furthermore, some symbionts use many of the same mechanisms as pathogens to infect hosts and evade immune responses. Here we discuss what is currently known about the interactions between bacterial symbionts and their hosts.     

Dynamic interactions between transposable elements and their hosts

Transposable elements (TEs) have a unique ability to mobilize to new genomic locations, and the major advance of second-generation DNA sequencing has provided insights into the dynamic relationship between TEs and their hosts. It now is clear that TEs have adopted diverse strategies - such as specific integration sites or patterns of activity - to thrive in host environments that are replete with mechanisms, such as small RNAs or epigenetic marks, that combat TE amplification. Emerging evidence suggests that TE mobilization might sometimes benefit host genomes by enhancing genetic diversity, although TEs are also implicated in diseases such as cancer. Here, we discuss recent findings about how, where and when TEs insert in diverse organisms.     

Interactions of Vibrio phages and their hosts in aquatic environments

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Balance between promiscuity and specificity in phage λ host range

As hosts acquire resistance to viruses, viruses must overcome that resistance to re-establish infectivity, or go extinct. Despite the significant hurdles associated with adapting to a resistant host, viruses are evolutionarily successful and maintain stable coevolutionary relationships with their hosts. To investigate the factors underlying how pathogens adapt to their hosts, we performed a deep mutational scan of the region of the λ tail fiber tip protein that mediates contact with the receptor on λ’s host, Escherichia coli. Phages harboring amino acid substitutions were subjected to selection for infectivity on wild type E. coli, revealing a highly restrictive fitness landscape, in which most substitutions completely abrogate function. A subset of positions that are tolerant of mutation in this assay, but diverse over evolutionary time, are associated with host range expansion. Imposing selection for phage infectivity on three λ-resistant hosts, each harboring a different missense mutation in the λ receptor, reveals hundreds of adaptive variants in λ. We distinguish λ variants that confer promiscuity, a general ability to overcome host resistance, from those that drive host-specific infectivity. Both processes may be important in driving adaptation to a novel host.Subject terms: Bacteriophages, Molecular evolution, Viral genetics     

A note on the isolation and propagation of lytic phages from Streptococcus uberis and their potential for strain typing

Thirty-eight of 98 strains of Streptococcus uberis were shown to be carrying lysogenic phage. Although propagating strains were rare, host modification by field strains sensitive to phage was used to increase the lytic spectra. When 120 nationally-collected strains were challenged with 25 phages, selected on the basis of differing lytic spectra and propagating strains, 30% were susceptible to at least one phage, increasing to 42% when 480 strains from a single farm were considered. A typing system based on susceptibility to lytic phage was considered feasible.     

A note on the isolation and propagation of lytic phages from Streptococcus uberis and their potential for strain typing

Thirty-eight of 98 strains of Streptococcus uberis were shown to be carrying lysogenic phage. Although propagating strains were rare, host modification by field strains sensitive to phage was used to increase the lytic spectra. When 120 nationally-collected strains were challenged with 25 phages, selected on the basis of differing lytic spectra and propagating strains, 30% were susceptible to at least one phage, increasing to 42% when 480 strains from a single farm were considered. A typing system based on susceptibility to lytic phage was considered feasible.     

Phage-borne factors and host LexA regulate the lytic switch in phage GIL01

The Bacillus thuringiensis temperate phage GIL01 does not integrate into the host chromosome but exists stably as an independent linear replicon within the cell. Similar to that of the lambdoid prophages, the lytic cycle of GIL01 is induced as part of the cellular SOS response to DNA damage. However, no CI-like maintenance repressor has been detected in the phage genome, suggesting that GIL01 uses a novel mechanism to maintain lysogeny. To gain insights into the GIL01 regulatory circuit, we isolated and characterized a set of 17 clear plaque (cp) mutants that are unable to lysogenize. Two phage-encoded proteins, gp1 and gp7, are required for stable lysogen formation. Analysis of cp mutants also identified a 14-bp palindromic dinBox1 sequence within the P1-P2 promoter region that resembles the known LexA-binding site of Gram-positive bacteria. Mutations at conserved positions in dinBox1 result in a cp phenotype. Genomic analysis identified a total of three dinBox sites within GIL01 promoter regions. To investigate the possibility that the host LexA regulates GIL01, phage induction was measured in a host carrying a noncleavable lexA (Ind(-)) mutation. GIL01 formed stable lysogens in this host, but lytic growth could not be induced by treatment with mitomycin C. Also, mitomycin C induced β-galactosidase expression from GIL01-lacZ promoter fusions, and induction was similarly blocked in the lexA (Ind(-)) mutant host. These data support a model in which host LexA binds to dinBox sequences in GIL01, repressing phage gene expression during lysogeny and providing the switch necessary to enter lytic development.     

Physiological and biochemical aspects of interactions between insect parasitoids and their hosts

In the present review, available literary data on physiological and biochemical interactions between parasitoids and their hosts are analyzed. In order to achieve successful development inside or on their hosts, parasitoids widely use various strategies aimed at suppressing host immunity. Suppression agents used by parasitoids include venom and ovarian fluid components as well as symbiotic microorganisms. The influence of parasitoids on the host organism is complicated, covering many physiological functions and inducing changes of the host metabolism and behavior. The influence of ecto- and endoparasitoids on the host organism is analyzed separately.     

Coevolution between slave-making ants and their hosts: host specificity and geographical variation

We explored the impact of a slave-making ant, Protomognathus americanus, on two of its hosts, Leptothorax longispinosus and L. ambiguus. We showed that, on average, slave-maker colonies conduct raids on 2.7 L. longispinosus and 1.4 L. ambiguus nests in a single year. The more common host, L. longispinosus, survives raiding and colony-founding events in a third of the cases, but the less common host rarely survives attacks from the slave-makers. We compare our results, collected in Vermont, to a study conducted in New York where the slave-maker pressure is much stronger. Our results suggest that in Vermont the slave-maker has a sparing strategy when raiding L. longispinosus, but not when raiding L. ambiguus. Thus coevolution between slave-making ants and their hosts shows host specificity and geographical variation.     

Evaluation of relations between plasmids and phage host range among clinical isolates of Enterobacter cloacae

The aim of this study was evaluation the plasmid influence on phage host range of clinical strains of Enterobacter cloacae. We found that strains included in restrictive pattern A, displayed reduced host range. Such reduced sensitivity make these strains excellent candidates for search restrictive-modification systems. High discriminative efficacy of isolated phages (specific for strains Enterobacter cloacae) make them useful tool for phage typing in epidemiological investigations.     

The mechanism of bacterial infection by filamentous phages involves molecular interactions between TolA and phage protein 3 domains

The early events in filamentous bacteriophage infection of gram-negative bacteria are mediated by the gene 3 protein (g3p) of the virus. This protein has a sophisticated domain organization consisting of two N-terminal domains and one C-terminal domain, separated by flexible linkers. The molecular interactions between these domains and the known bacterial coreceptor protein (TolA) were studied using a biosensor technique, and we report here on interactions of the viral coat protein with TolA, as well as on interactions between the TolA molecules. We detected an interaction between the pilus binding second domain (N2) of protein 3 and the bacterial TolA. This novel interaction was found to depend on the periplasmatic domain of TolA (TolAII). Furthermore, extensive interaction was detected between TolA molecules, demonstrating that bacterial TolA has the ability to interact functionally with itself during phage infection. The kinetics of g3p binding to TolA is also different from that of bacteriocins, since both N-terminal domains of g3p were found to interact with TolA. The multiple roles for each of the separate g3p and TolA domains imply a delicate interaction network during the phage infection process and a model for the infection mechanism is hypothesized.     

Give-and-take: interactions between DNA transposons and their host plant genomes

Recent genome sequencing efforts have revealed how extensively transposable elements (TEs) have contributed to the shaping of present day plant genomes. DNA transposons associate preferentially with the euchromatic or genic component of plant genomes and have had the opportunity to interact intimately with the genes of the plant host. These interactions have resulted in TEs acquiring host sequences, forming chimeric genes through exon shuffling, replacing regulatory sequences, mobilizing genes around the genome, and contributing genes to the host. The close interaction of transposons with genes has also led to the evolution of intricate cellular mechanisms for silencing transposon activity. Transposons have thus become important subjects of study in understanding epigenetic regulation and, in cases where transposons have amplified to high numbers, how to escape that regulation.     

The dialogue between viruses and hosts in compatible interactions

Understanding the biological principles behind virus-induced symptom expression in plants remains a longstanding challenge. By dissecting the compatible host-virus relationship temporally and genetically, we have begun to map out the relationships of its component parts. The picture that emerges is one in which host gene expression and physiology are under tight temporal control during infection.     

Genetic differentiation between two host “races” and two species of cleptoparasitic bees and between their two hosts

In this paper we test the following two hypotheses: (1) that apparently conspecific samples of the cleptoparasitic beeCoelioxys funeraria, differing markedly in size and reared from different host species, do indeed represent one panmictic population; (2) that bees that nest in holes in wood or twigs have higher levels of genetic variation than those nesting in the ground. Based upon 41 loci, the genetic differences between the two samples ofC. funeraria could be explained entirely in terms of sampling error. In contrast, the sympatricC. moesta showed 16 fixed allelic differences from theC. funeraria samples. Similarly, the two hosts ofC. funeraria, Megachile relativa andM. inermis, had 21 fixed allelic differences between them out of 42 presumptive gene loci. Heterozygosities among the wood-nesting bees were not particularly high for Hymenoptera, ranging from 0.045 to 0.054. Comparisons of heterozygosity estimates among bees remain ambiguous as to whether soil nesting confers sufficient environmental buffering effects to reduce possible advantages of heterosis in ground-nesting species.     

Friend or foe: using systems biology to elucidate interactions between fungi and their hosts

Modelling the networks sustaining the fruitful coexistence between fungi and their mammalian hosts is becoming increasingly important to control emerging fungal pathogens. In a 'systems biology' perspective, the microbiota and host should be seen as an ecosystem, and disease considered as an alteration of the equilibrium. This review addresses host-fungus interaction with a special focus on systems biology approaches to investigate the mechanisms developed by Candida albicans and Aspergillus fumigatus to circumvent host immune responses during fungal infections. Such genome-wide integrative approaches hold the promise to significantly improve our ability to understand which fungal traits can be considered potential threats and the regulatory networks involved in immune subversion.     

An evolving picture of the interactions between malaria parasites and their host erythrocytes

In patients with malaria, Plasmodium falciparum parasites multiply to enormous numbers in the bloodstream, initiating processes of erythrocyte destruction, endothelial activation and microvascular inflammation that cause devastating pathological effects on host tissues and organs. Recent research casts new light on a mechanism by which hemoglobin mutations may protect against these effects, and on a critical receptor-ligand interaction that provides fresh opportunities for the development of vaccines against blood-stage infection.The symptoms of malaria occur in the period of the Plasmodium life cycle when erythrocytes are infested by parasites. This period commences when parasites emerge from the liver after replicating from the sporozoites introduced by a mosquito bite. The new blood-stage parasites multiply quickly as haploid, asexual forms in one-, two- or three-day cycles (depending on the Plasmodium species) and increase their numbers enormously, often infecting 1% or more of the trillions of erythrocytes in the bloodstream. These populations of asexual forms are required for the production of sexual gametocyte forms that enter feeding mosquitoes, in which the parasites mate and produce new sporozoites for transmission to other human hosts. While large numbers of erythrocytes support the propagation and survival of malaria parasites, the inflammatory and erythrocyte-destroying effects of the parasite biomass cause devastating pathological effects on host tissues and organs.These pathological effects and the deaths that they cause have exerted powerful selection pressure on the human genome over thousands of generations. Outcomes of this pressure include the sickle cell hemoglobin (HbS) mutation, which protects young children against the life-threatening complications of Plasmodium falciparum malaria, and various blood group antigens, which affect the ligand-receptor interactions utilized by different Plasmodium parasites for erythrocyte invasion. Two recent papers in Science and Nature offer fresh and interesting discoveries from research in these areas: (i) a molecular mechanism by which mutation of hemoglobin may protect against malaria ¹, and (ii) a newly discovered ligand-receptor interaction that may be critical for P. falciparum invasion of human erythrocytes ².HbS represents a classic example of a balanced polymorphism: the heterozygous sickle cell trait (HbAS, from the inheritance of one normal HbA and one sickle HbS β-globin-coding gene) protects against severe life-threatening malaria, while the homozygous HbAA condition offers no protection from malaria and the homozygous HbSS condition produces frequent fatalities from sickle cell anemia ³. Although early studies implicated poor growth of P. falciparum in HbAS erythrocytes as a mechanism of protection that keeps parasitemias low, other work found that laboratory-adapted parasite clones grew normally in HbAS erythrocytes even under reduced oxygen conditions ^{4, 5}. Further, it was clear that substantial parasitemias and frequent episodes of uncomplicated malaria occurred in HbAS as well as HbAA children, despite marked differences in the incidence of severe malaria between these groups ⁶. Differential protection against severe malaria is also provided by hemoglobin C (HbC) in West Africa ⁷. These field observations suggest a mechanism of protection that, instead of merely reducing the numbers of parasitized erythrocytes in the circulation, works to ameliorate the inflammation that arises at the host-parasite interface from the interactions of infected erythrocytes with the endothelium and other blood elements. Indeed, parasitized HbAC and HbAS erythrocytes show significant impairment of cytoadherence in association with perturbed display of the P. falciparum major cytoadherence protein (PfEMP1) on abnormal knob protrusions ^{5, 8}.Using cryo-electron tomography, Cryklaff et al. ¹ show that P. falciparum hijacks and remodels erythrocyte actin into a network that may support the trafficking of PfEMP1 and other virulence proteins to the host cell membrane, where these proteins form the knobs involved in sequestration-related events and inflammation (Figure 1). Branching patterns of actin were found in association with Maurer''s clefts, membranous compartments that have an important role in exporting proteins from the parasite to the periphery of the host cell cytoplasm ⁹. Further, Cryklaff et al. ¹ observed significantly reduced actin remodeling and aberrant Maurer''s clefts in HbCC and HbSC erythrocytes, suggesting that these mutant hemoglobin states may interfere with the installation of actin scaffolds that help to tether Maurer''s clefts and support vesicle and protein trafficking to the erythrocyte membrane.Open in a separate windowFigure 1Junctures of pathogenesis in P. falciparum malaria: cytoadherence of parasitized erythrocytes to microvascular endothelium and parasite invasion of erythrocytes. P. falciparum parasites display knobs at the surface of their host erythrocytes as they mature from ring to trophozoite and schizont forms. PfEMP1 cytoadherence proteins are concentrated on knobs, where they bind receptors (e.g., CD36 and ICAM-1), activate endothelial cells, and recruit blood elements including platelets and white blood cells. By adhering in microvessels, the mature parasites avoid being carried by the bloodstream to the spleen where they are destroyed. Sequestration-related events lead to upregulation of tissue factor, resulting in thrombin and complement activation, platelet activation, cytokine production, endothelial dysfunction and inflammation ¹⁴. To support the transport of PfEMP1 and other proteins including the knob-associated histidine-rich protein (KAHRP) to the erythrocyte membrane, P. falciparum parasites tether membranous Maurer''s clefts beneath the cytoskeleton ⁹. In knobs, PfEMP1 associates with KAHRP anchored to spectrin-actin-protein 4.1 complexes, to spectrin-actin junctions, and to the band 3-binding domain of ankyrin ^{15, 16}. Cryklaff et al. ¹ report that P. falciparum remodels host actin into a network of filaments associated with Maurer''s clefts and the erythrocyte membrane; this network may support protein and vesicle trafficking to the knobs. Hemoglobin variants HbS and HbC interfere with proper knob formation and PfEMP1 display, weaken the binding of parasitized erythrocytes to endothelium and may thereby reduce sequestration-related pathology ^{5, 8}. Aberrant Maurer''s clefts and compromised remodeling of the actin network occur in HbSC and HbCC erythrocytes ¹; these abnormalities remain to be demonstrated in HbAS and HbAC erythrocytes. Inset (left) is adapted from ref ¹⁷. Merozoites released from mature schizonts invade erythrocytes by steps of initial contact, reorientation with attachment, junction formation, and entry and membrane resealing. Most members of the PfEBL and PfRH protein families have overlapping and individually dispensable functions that support a diversity of invasion pathways by attachment to different blood group antigens. These events are followed by binding of P. falciparum AMA1 and RON proteins at the attachment interface, triggering junction formation (not shown) ¹⁸. The interaction of the PfRH5-PfRipr complex ¹² with basigin ² appears to be essential for invasion and may have a critical function beyond the roles of binding and attachment that characterize other members of the PfEBL and PfRH families. Inset (right) is adapted from ref ¹⁸.Are there also significant differences between the actin networks and/or Maurer''s clefts of HbAS, HbAC and HbAA erythrocytes? HbAS and HbAC are, after all, the prevalent malaria-protective states of HbS and HbC. On this question the report of Cryklaff et al. ¹ is unfortunately silent; actin remodeling and Maurer''s clefts in HbAS and HbAC erythrocytes still need to be investigated, as do the effects of HbAS and HbAC erythrocyte extracts on actin polymerization in vitro. Mechanisms apart from disturbed actin remodeling may still account for abnormal PfEMP1 display and knob formation on parasitized HbAC and HbAS erythrocytes. For example, hemichromes generated more readily from oxidation of HbC or HbS may physically hinder the docking of virulence proteins and thus interrupt the formation of regular knob arrays in the erythrocyte cytoskeleton (where hemichromes are known to bind). Another possibility is that HbC and HbS elevate the levels of oxidative stress in parasitized erythrocytes, damaging membranes and biochemically hampering the functions of Maurer''s clefts and their associated vesicles in the transport of knob-forming proteins. The challenge for the research field in the coming years will be to sort out these possible mechanisms and their contributions to malaria protection by the heterozygous HbAS and HbAC conditions.P. falciparum invades erythrocytes by various pathways involving different ligand-receptor interactions ¹⁰. Partner ligands in these interactions include members of two molecular families known as the EBA (erythrocyte binding antigen) and RBL (reticulocyte binding-like) proteins. In P. falciparum, members of these families are termed PfEBL (P. falciparum erythrocyte binding-like) and PfRH (P. falciparum reticulocyte binding-like homolog) proteins. Evidence suggests that the roles of many of these proteins are overlapping: P. falciparum lines can often invade erythrocytes that lack receptors for specific PfEBL or PfRH proteins (because of inherent mutations or enzyme treatment) and, conversely, knockout parasites that do not express individual PfEBL or PfRH proteins have been found to efficiently invade erythrocytes. It thus came as a surprise that focused efforts to knock out the gene encoding an atypical, foreshortened member of the PfRH family, PfRH5, did not succeed in two laboratories ^{10, 11}. While polymorphisms in PfRH5 could be linked to receptor preferences and an ability of a P. falciparum line to also invade Aotus monkey erythrocytes ¹¹, the function of PfRH5 as a parasite ligand and the erythrocyte receptor(s) that it uses for invasion remained unknown.Crosnier et al. ² have now identified the PfRH5 receptor by applying an avidity-based extracellular interaction screen (AVEXIS) to the expressed proteins of an erythrocyte ectodomain library. Results show that PfRH5 binds an isoform of basigin on erythrocytes (BSG-S, the Ok blood group antigen, CD147) and that P. falciparum appears to generally require this interaction to efficiently invade human erythrocytes. In contrast to the effects of glycan removal (by neuraminidase) from Aotus erythrocytes on PfRH5 binding and parasite invasion by particular P. falciparum lines ¹¹, removal of all glycans from human basigin does not alter PfRH5 binding ². Further, in experiments with multiple P. falciparum clones, Crosnier et al. show that the invasion of human erythrocytes is potently inhibited by a soluble pentamerized form of basigin, by anti-basigin monoclonal antibodies, and by reduction of basigin levels on the erythrocyte surface ².Two of five single amino acid polymorphisms (E92K, L90P) in basigin affected PfRH5 binding to or invasion of human erythrocytes. While one of these polymorphisms (E92K) is associated with a relatively rare Ok^a- blood group in Japan, there are no data to suggest that L90P (or perhaps another undiscovered basigin polymorphism) was naturally selected to high prevalence in malaria-endemic areas. Although the native function of basigin on human erythrocytes is unknown, its high level of conservation suggests that P. falciparum may have evolved to depend on basigin to a much greater extent than on other, more polymorphic receptors. Interestingly, PfRH5 is also unlike other members of the PfEBL and PfRH families in that it lacks a transmembrane domain; recent evidence indicates that it forms a complex with a processed EGF-like PfRH5-interacting protein (PfRipr) and that this complex, in turn, associates tightly with another partner on the merozoite membrane ¹² (Figure 1). Attempts to disrupt the PfRipr gene also have been unsuccessful ¹².These findings suggest a critical role for the PfRH5-PfRipr complex that goes beyond an additional contribution of mechanical attachment within the binding repertoire of PfEBL and PfRH proteins. Possibilities for essential function might include PfRH5-PfRipr participation in a signaling pathway required for invasion, or an essential partnership in the junction during merozoite entry (Figure 1). Recent results also show promise for the use of PfRH5 and PfRipr as targets for intervention: rabbit IgG antibodies against virally-vectored, full-length PfRH5 outperformed antibodies that were generated by the same strategy against nine other erythrocytic-stage vaccine candidates, including four other PfEBL and PfRH proteins ¹³; rabbit antibodies against PfRipr likewise inhibited merozoite attachment and parasite growth in culture ¹². Although variations in the susceptibility of different P. falciparum lines were observed in these studies (likely due to different utilization patterns of ligand-receptor interactions), striking neutralization was nevertheless achieved in all cases. These results support PfRH5 and other components of its binding complex as new targets for therapeutic intervention and give an important boost to vaccine efforts against the asexual blood stages of P. falciparum.