Surface antigen cross-linking triggers forced exit of a protozoan parasite from its host.

We used the common fish pathogen Ichthyophthirius multifiliis as a model for studying interactions between parasitic ciliates and their vertebrate hosts. Although highly pathogenic, Ichthyophthirius can elicit a strong protective immune response in fish after exposure to controlled infections. To investigate the mechanisms underlying host resistance, a series of passive immunization experiments were carried out using mouse monoclonal antibodies against a class of surface membrane proteins, known as immobilization antigens (or i-antigens), thought to play a role in the protective response. Such antibodies bind to cilia and immobilize I. multifiliis in vitro. Surprisingly, we found that passive antibody transfer in vivo caused rapid exit of parasites from the host. The effect was highly specific for a given I. multifiliis serotype. F(ab)2 subfragments had the same effect as intact antibody, whereas monovalent Fab fragments failed to protect. The activity of Fab could, nevertheless, be restored after subsequent i.p. injection of bivalent goat anti-mouse IgG. Parasites that exit the host had detectable antibody on their surface and appeared viable in all respects. These findings represent a novel instance among protists in which protective immunity (and evasion of the host response) result from an effect of antibody on parasite behavior.

Parasite abundance and diversity in mammals: correlates with host ecology.

Fecally dispersed parasites of 12 wild mammal species in Mudumalai Sanctuary, southern India, were studied. Fecal propagule densities and parasite diversity measures were correlated with host ecological variables. Host species with higher predatory pressure had lower parasite loads and parasite diversity. Host body weight, home range, population density, gregariousness, and diet did not show predicted effects on parasite loads. Measures of alpha diversity were positively correlated with parasite abundance and were negatively correlated with beta diversity. Based on these data, hypotheses regarding determinants of parasite community are discussed.

Manipulation of host hepatocytes by the malaria parasite for delivery into liver sinusoids.

The merozoite stage of the malaria parasite that infects erythrocytes and causes the symptoms of the disease is initially formed inside host hepatocytes. However, the mechanism by which hepatic merozoites reach blood vessels (sinusoids) in the liver and escape the host immune system before invading erythrocytes remains unknown. Here, we show that parasites induce the death and the detachment of their host hepatocytes, followed by the budding of parasite-filled vesicles (merosomes) into the sinusoid lumen. Parasites simultaneously inhibit the exposure of phosphatidylserine on the outer leaflet of host plasma membranes, which act as "eat me" signals to phagocytes. Thus, the hepatocyte-derived merosomes appear to ensure both the migration of parasites into the bloodstream and their protection from host immunity.

Host relations of the parasitic cowbirds /

At head of title: Museum of Natural History.

Parasite-host interaction of the protoplast isolates of Entomophthora egressa with the eastern hemlock looper and the eastern spruce budworm

Hemocytes of the insects Lambdina fiscellaria fiscellaria and Choristoneura fumiferana did not adhere to the protoplasts of ~he fungus EntomoEhthora egressa. Hemocyte reaction for both insect species to test-particles was not suppressed by the protoplasts. The spherule cells of _-L. fiscellaria fiscellaria adhered to the spherical hyphal bodies and hyphae of ~· ~gressa. The granular cells of -c. fumiferana adhered to the hyphae of ~· egress~. Protoplasts exposed to papain were attacked by the granular ·cells of -c. fumiferana. Spent growth medium of both protoplast isolates produced paralysis when injected into -c. fumiferana larvae. Evidence suggests that heat-stable proteins may be involved. Protoplast isolates showed differences in the growth rates and regeneration sequences using coagulated egg yolk medium, a highly modified version of Grace's insect tissue . culture medium (MGM) and modifications of MGM and in the presence of C0₂. The isolates also differed in the changes that they induced in MGM composition during protoplast growth and in the rates of glucose utilization and protein secretion. The serum of c. fumiferana larvae contained protein(s) which we believe adhere to the cell membranes of the protoplasts of E. egressa. Evidence is presented for hemocyteplasn~ interaction in the presence of protoplasts. Components in the larval serum were found to influence protoplast growth patterns. The possibility of antiprotoplast serum activity is presented. Melanin, toxic levels of ninhydrinpositive compounds and antiprotoplast proteins may have been involved in this activity. The granular cells of -L. fiscellaria fiscellaria and Q• fumiferana adhered to the hyphae of ,Rhizopus ~i$rican~. Spores of Absidia repens and the bacteria Escherichia coli and Bacillus cereus adhered to the granular cells of both species of· insects. The granular cells and plasmatocytes of -c. fumiferana were capable of phagocytosing -B. cereus. Adhesion of .A... . repens spores to c. fumiferana granular cells ~ . - was stimulated by N-acetylglucosamine and glucosamine, moderately reduced by D-fucose, D-arabinose, D-mannose, D-galatose and sucrose and mildly reduced by D-glucose, D-fructose and trehalose. There was no evidence of humoral opsonins in larval hemolymph favoring test-particle-hemocyte interaction. Granular cells of c. fumiferana exposed to papain had reduced affinities for A. repens spores.

Two mistletoes are too many?: Interspecific occurrence of mistletoes on the same host tree

Mistletoe can have a major impact on the fitness of the host plant. If there is more than one species of mistletoe on the same host tree, the overall impact might be amplified. We report the occurrence of more than one species of mistletoe on the same host tree. Although it is not a rule in the field, to our knowledge, there have been no studies of this topic. In most cases, two species of mistletoe were recorded on the same host tree, although we recorded three species of mistletoe on one occasion. This demonstrates that different species of mistletoe can be compatible with the same host species. Therefore, compatibility (structural and physiological) might be an important factor for the occurrence of mistletoe. Recent studies have shown that if the mistletoe does not recognize the host species, the deposited seeds will germinate but the haustorium will not penetrate the host branch. This is probably the primary mechanism in the establishment of more than one species of mistletoe on the same host, which can trigger a cascade of harmful effects for the host species.

A century of research: what have we learned about the interaction of Trypanosoma cruzi with host cells?

Since the discovery of Trypanosoma cruzi and the brilliant description of the then-referred to "new tripanosomiasis" by Carlos Chagas 100 years ago, a great deal of scientific effort and curiosity has been devoted to understanding how this parasite invades and colonises mammalian host cells. This is a key step in the survival of the parasite within the vertebrate host, and although much has been learned over this century, differences in strains or isolates used by different laboratories may have led to conclusions that are not as universal as originally interpreted. Molecular genotyping of the CL-Brener clone confirmed a genetic heterogeneity in the parasite that had been detected previously by other techniques, including zymodeme or schizodeme (kDNA) analysis. T. cruzi can be grouped into at least two major phylogenetic lineages: T. cruzi I, mostly associated with the sylvatic cycle and T. cruzi II, linked to human disease; however, a third lineage, T. cruziIII, has also been proposed. Hybrid isolates, such as the CL-Brener clone, which was chosen for sequencing the genome of the parasite (Elias et al. 2005, El Sayed et al. 2005a), have also been identified. The parasite must be able to invade cells in the mammalian host, and many studies have implicated the flagellated trypomastigotes as the main actor in this process. Several surface components of parasites and some of the host cell receptors with which they interact have been described. Herein, we have attempted to identify milestones in the history of understanding T. cruzi- host cell interactions. Different infective forms of T. cruzi have displayed unexpected requirements for the parasite to attach to the host cell, enter it, and translocate between the parasitophorous vacuole to its final cytoplasmic destination. It is noteworthy that some of the mechanisms originally proposed to be broad in function turned out not to be universal, and multiple interactions involving different repertoires of molecules seem to act in concert to give rise to a rather complex interplay of signalling cascades involving both parasite and cellular components.

The Function and Three-Dimensional Structure of a Thromboxane A(2)/Cysteinyl Leukotriene-Binding Protein from the Saliva of a Mosquito Vector of the Malaria Parasite

The highly expressed D7 protein family of mosquito saliva has previously been shown to act as an anti-inflammatory mediator by binding host biogenic amines and cysteinyl leukotrienes (CysLTs). In this study we demonstrate that AnSt-D7L1, a two-domain member of this group from Anopheles stephensi, retains the CysLT binding function seen in the homolog AeD7 from Aedes aegypti but has lost the ability to bind biogenic amines. Unlike any previously characterized members of the D7 family, AnSt-D7L1 has acquired the important function of binding thromboxane A(2) (TXA(2)) and its analogs with high affinity. When administered to tissue preparations, AnSt-D7L1 abrogated Leukotriene C(4) (LTC(4))-induced contraction of guinea pig ileum and contraction of rat aorta by the TXA(2) analog U46619. The protein also inhibited platelet aggregation induced by both collagen and U46619 when administered to stirred platelets. The crystal structure of AnSt-D7L1 contains two OBP-like domains and has a structure similar to AeD(7). In AnSt-D7L1, the binding pocket of the C-terminal domain has been rearranged relative to AeD7, making the protein unable to bind biogenic amines. Structures of the ligand complexes show that CysLTs and TXA(2) analogs both bind in the same hydrophobic pocket of the N-terminal domain. The TXA(2) analog U46619 is stabilized by hydrogen bonding interactions of the omega-5 hydroxyl group with the phenolic hydroxyl group of Tyr 52. LTC(4) and occupies a very similar position to LTE(4) in the previously determined structure of its complex with AeD7. As yet, it is not known what, if any, new function has been acquired by the rearranged C-terminal domain. This article presents, to our knowledge, the first structural characterization of a protein from mosquito saliva that inhibits collagen mediated platelet activation.

Identification of the Schistosoma mansoni TNF-Alpha Receptor Gene and the Effect of Human TNF-Alpha on the Parasite Gene Expression Profile

Background: Schistosoma mansoni is the major causative agent of schistosomiasis. The parasite takes advantage of host signals to complete its development in the human body. Tumor necrosis factor-alpha (TNF-alpha) is a human cytokine involved in skin inflammatory responses, and although its effect on the adult parasite's metabolism and egg-laying process has been previously described, a comprehensive assessment of the TNF-alpha pathway and its downstream molecular effects is lacking. Methodology/Principal Findings: In the present work we describe a possible TNF-alpha receptor (TNFR) homolog gene in S. mansoni (SmTNFR). SmTNFR encodes a complete receptor sequence composed of 599 amino acids, and contains four cysteine-rich domains as described for TNFR members. Real-time RT-PCR experiments revealed that SmTNFR highest expression level is in cercariae, 3.5 (+/- 0.7) times higher than in adult worms. Downstream members of the known human TNF-alpha pathway were identified by an in silico analysis, revealing a possible TNF-alpha signaling pathway in the parasite. In order to simulate parasite's exposure to human cytokine during penetration of the skin, schistosomula were exposed to human TNF-alpha just 3 h after cercariae-to-schistosomula in vitro transformation, and large-scale gene expression measurements were performed with microarrays. A total of 548 genes with significantly altered expression were detected, when compared to control parasites. In addition, treatment of adult worms with TNF-alpha caused a significantly altered expression of 1857 genes. Interestingly, the set of genes altered in adults is different from that of schistosomula, with 58 genes in common, representing 3% of altered genes in adults and 11% in 3 h-old early schistosomula. Conclusions/Significance: We describe the possible molecular elements and targets involved in human TNF-alpha effect on S. mansoni, highlighting the mechanism by which recently transformed schistosomula may sense and respond to this host mediator at the site of cercarial penetration into the skin.

Counterregulation of Th2 immunity by interleukin 12 reduces host defenses against Strongyloides venezuelensis infection

The aim of this study was to investigate the role of interleukin 12 (IL-12) during Strongyloides venezuelensis infection. IL-12(-/-) and wildtype C57BL/6 mice were subcutaneously infected with 1500 larvae of S. venezuelensis. On days 7, 14, and 21 post-infection, we determined eosinophil and mononuclear cell numbers in the blood and broncoalveolar lavage fluid (BALF), Th2 cytokine secretion in the lung parenchyma, and serum antibody levels. The numbers of eggs in the feces and worm parasites in the duodena were also quantified. The eosinophil and mononuclear cell counts and the concentrations of IL-3, IL-5, IL-10, IL-13, and IgG1 and IgE antibodies increased significantly in infected IL-12(-/-) and wild-type mice as compared with uninfected controls. However, the number of eosinophils and mononuclear cells in the blood and BALF and the Th2 cytokine levels in the lungs of infected IL-12-/- mice were greater than in infected wild-type C57BL/6 mice. In addition, serum IgE and IgG1 levels were also significantly enhanced in the infected mice lacking IL-12. Meanwhile, parasite burden and fecal egg counts were significantly decreased in infected IL-12-/- mice. Together, our results showed that the absence of IL-12 upregulates the Th2 immune response, which is important for control of S. venezuelensis infection. (C) 2009 Elsevier Masson SAS. All rights reserved.

Infection of the epaulette shark, Hemiscyllium ocellatum (Bonnaterre), by the nematode parasite Proleptus australis Bayliss (Spirurida : Physalopteridae)

Seventy-two epaulette sharks, Hemiscyllium ocellatum (Bonnaterre), were infected with the nematode parasite Proleptus australis Bayliss, 1933. The parasite population was overdispersed. Infection intensity ranged from 3 to 1002 worms per fish stomach, and there was a positive correlation between shark length and number of parasites present. The majority of worms were attached to the stomach wall, and scanning electron microscopy and histological examination showed that worms penetrated the stomach lining. Worms were observed within the lamina propria of the stomach and occasionally penetrated the muscularis mucosa. Little to no inflammatory or cellular immune reaction to the presence of the parasites was observed, except in one case where a worm was being degraded by a host tissue response. There was a large amount of connective tissue proliferation as a result of nematode attachment,, but no obvious effects on the overall health of the sharks were seen. Three sharks were also found to be infected by the cestode Callitetrarhynchus sp.

A new social parasite in the ant genus Ectatomma F. Smith (Hymenoptera, Formicidae, Ectatomminae)

Ectatomma parasiticum Feitosa & Fresneau, a new ant species socially parasitic on Ectatomma tuberculatum (Olivier), is described from gynes discovered in Apazapan, state of Veracruz, Mexico, and reared in the laboratory. Ectatomma parasiticum is the first social parasite described in the Ectatomminae. This species can be distinguished from its host by morphological and behavioral features characteristic of the inquilines known in other ant subfamilies including reduced size, thickened petiole, and agonistic interactions with host species.

Natural Host Relationships and Genetic Diversity of Rodent-Associated Hantaviruses in Southeastern Brazil

Objective: Hantaviruses are rodent-borne RNA viruses that have caused hantavirus cardiopulmonary syndrome in several Brazilian regions. In the present study, geographical distribution, seroprevalence, natural host range, and phylogenetic relations of rodent-associated hantaviruses collected from seven counties of Southeastern Brazil were evaluated. Methods: ELISA, RT-PCR and phylogenetic analysis were used in this study. Results: Antibodies to hantavirus were detected in Bolomys lasiurus, Akodon sp. and Oligoryzomys sp., performing an overall seroprevalence of 5.17%. All seropositive rodents were associated with grasslands or woods surrounded by sugar cane fields. Phylogenetic analysis of partial S- and M-segment sequences showed that viral sequences isolated from B. lasiurus specimens clustered with Araraquara virus. However, a sequence from Akodon sp. shared 100% similarity with Argentinian/Chilean viruses based on the partial S- segment amino acid sequence. Conclusion: These results indicate that there are associations between rodent reservoirs and hantaviruses in some regions of Southeastern Brazil, and suggest the existence of additional hantavirus genetic diversity and host ecology in these areas. Copyright (C) 2008 S. Karger AG, Basel

Dendromonocotyle colorni sp n. (Monogenea : Monocotylidae) from the skin of Himantura uarnak (Dasyatididae) from Israel and a new host record for D-octodiscus from the Bahamas

Dendromonocotyle colorni sp. n. (Monogenea: Monocotylidae) is described from the dorsal skin surface of two specimens of Himantura uarnak (Forsskal) kept at the Eilat Underwater Observatory in Israel. Dendromonocotyle colorni is distinguished from the other eight species in the genus by the morphology of the terminal papillar sclerite on the haptor, the distal portion of the male copulatory organ and the morphology of the vagina. The development of the male copulatory organ is detailed for D. colorni and the adaptations of species of Dendromonocotyle to life on the dorsal skin surface of rays are discussed. Dendromonocotyle octodiscus Hargis, 1955 was identified from the dorsal skin surface of the southern stingray Dasyatis americana Hildebrand et Schroeder off Bimini, Bahamas and represents a new host record.