Inhibitory and neutral antibodies to Plasmodium falciparum MSP119 form ring structures with their antigen

Blood-stage malaria vaccine candidates include surface proteins of the merozoite. Antibodies to these proteins may either block essential steps during invasion or render the merozoite susceptible to phagocytosis or complement-mediated degradation. Structural information on merozoite surface proteins complexed to antibodies provides crucial information for knowledge-based vaccine design. The major merozoite surface protein MSP1 is an abundant surface molecule in Plasmodium falciparum. Only a subset of antibodies against MSP119 inhibits invasion (inhibitory antibodies), whereas other antibodies binding to MSP119 have no effect on invasion (neutral antibodies). Here we report on the complex of MSP119 with both inhibitory monoclonal antibody 12.10 and neutral monoclonal antibody 2F10. The complexes were established using both whole IgG's and Fab fragments, and analysed by dynamic light scattering, electron microscopy and analytical ultra centrifugation. Specific ring structures were formed in the ternary complex with the two antibodies, providing direct evidence of non-overlapping epitopes on MSP119. Mutational studies also indicated that the epitopes of the inhibitory and neutral antibodies are spatially remote.     

Monoclonal Antibodies to Trypanosoma cruzi Inhibit Motility and Nucleic Acid Synthesis of Culture Forms

Monoclonal antibodies were raised against the surface of epimastigotes and metacylic trypomastigotes of Trypanosoma cruzi, as shown by electron microscopy, agglutination, and immunofluorescence. The antibodies were stage specific but not strain specific. A deleterious effect of the antibodies on T. cruzi culture forms was shown by the drastic reduction of parasite motility and incorporation of nucleic acid precursors. Some fraction of the parasite population, however, was viable and replicated and infected mouse macrophages in culture. The antibodies were found to also mediate complement-induced lysis of culture forms of T. cruzi.     

Genetic polymorphisms of orosomucoid and alpha-2-HS-glycoprotein in Thai,Sri Lankan and Paraguayan populations

The genetic polymorphism of orosomucoid (ORM) and alpha-2-HS-glycoprotein (AHSG) were studied in Thai, Sri Lankan and Paraguayan populations using isoelectric focusing. Gene frequencies in these populations were compared with those in other populations. Four new ORM variants were detected:ORM1 ^* 15 in Thai,ORM1 ^* 16 in Paraguayan,ORM2 ^* 21 andORM2 ^* 22 in Sri Lankan.     

Acanthamoeba sp. from the Philippines: electron microscopy studies on naturally occurring bacterial symbionts

The isolation of two plasmind-like ciruclar DNAs, measuring 52 and 42 kbp, from anAcanthamoeba sp. from the Philippines has led to the demonstration of a bacterial endosymbiont occurring in this free-living amoeba. The 52-kbp band hybridized with a short sequence of cytochrome b gene and was identified as the mitochondrial DNA, whereas the 42-kbp band was identified as plasmid DNA of the bacterial symbionts on the basis of electron microscopy. The endosymbionts are gram-negative, rod-shaped bacteria measuring approximately 1.3×0.43 m and numbering about eight to ten cells per section. They are randomly distributed in both cysts and trophozoites and are surrounded neither by a phagolysosomal membrane nor by a clear or electrontranslucent region. The endosymbiont membrane appears to have a close association with ribosomes, which are seen to be more concentrated within the vicinity of the symbionts than elsewhere within the cytoplasm. Attempts to grow the symbionts and the amoebae separately have failed.     

Comparison of polymerase chain reaction with light microscopy for detection of microsporidia in clinical specimens

The detection of microsporidial DNA by the polymerase chain reaction (PCR) has been suggested as an alternative or supplement to conventional microscopic methods. However, the relative merits of these techniques remain uncertain. In the present study, clinical specimens of different origin (stool, urine, sputum, nasal discharge, and cerebrospinal fluid) containing four different microsporidial species were blinded after microscopic examination and analyzed by PCR and subsequent restriction fragment length polymorphism (RFLP) to determine the respective species. Thirty-four specimens from 31 patients were evaluated, 16 of which were positive and 18 negative by microscopic examination; PCR detection of microsporidia produced identical results in 82% (28/34) of these specimens. Four samples were microscopically negative, PCR-positive, and two were microscopically positive, PCR-negative. Species determination by RFLP analysis of the amplified product was accurate for all isolates containingEnterocytozoon bieneusi, Encephalitozoon intestinalis, Encephalitozoon hellem, andEncephalitozoon cuniculi compared with microscopic identification of the genusEnterocytozoon or molecular analysis ofEncephalitozoon species after in vitro culture. Therefore, PCR-RFLP is useful for the rapid detection and differentiation of microsporidian spores in clinical specimens.     

Differential plasticity and fate of brain-resident and recruited macrophages during the onset and resolution of neuroinflammation

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Cloning and sequencing of putative acetylcholinesterase cDNAs from the American dog tick, Dermacentor variabilis, and the brown dog tick, Rhipicephalus sanguineus (Acari: Ixodidae)

Two putative cDNAs of acetylcholinesterase (AChE), one from Dermacentor variabilis, and the other from Rhipicephalus sanguineus, were amplified and sequenced. The deduced amino acid sequences have high amino acid identities (between 70 and 94%) to known tick AChE sequences deposited in GenBank. Furthermore, these two AChEs also possess common features in their primary AChE structure such as catalytic active sites. A 2,220-bp contiguous sequence, containing a 1,791-bp open reading frame encoding an AChE precursor with 596 amino acid residues, was obtained from D. variabilis. The deduced proteins of R. sanguineus are different in size by 6 amino acids because of alternative splicing at the 5' end. A gene tree deduced from phylogenetic analysis indicates that there are at least three lineages of AChE in arthropods.     

Experimental infection of immunomodulated NOD/LtSz-SCID mice as a new model for Plasmodium falciparum erythrocytic stages

The main objective of this study was to determine whether a chemical immunomodulation protocol could reduce the resistance of NOD/LtSz-SCID mice to Plasmodium falciparum infection and provide an improved mouse model for screening the antimalarial activity of new compounds. This model was compared with the presently used immunodeficient Beige/Nude/Xid (BNX) mouse model, using the same protocol, in terms of percentage of infected mice, parasite development, leukocyte response and phagocytosis of P. falciparum infected cells in various organs. Our results show that the combination of the chemical immune modulation protocol with the genetic background of NOD/LtSz-SCID mice results in the development of long-lasting P. falciparum infection in a high percentage of mice. A comparison of the results obtained in the histological study for both mouse models suggests that the higher rate of success in NOD/LtSz-SCID mice could be related to the reduced macrophage recruitment developed in different tissues to remove the parasite from blood.     

Incubation in rats of a nematodal larva from cod to establish its specific identity:Contracaecum osculatum, (Rudolphi)

Infective, third-stage larvae of the genusContracaecum from fish were cultured in vitro and fed to laboratory animals in order to obtain later developmental stages to permit their specific identification. The in vitro incubation was unsuccessful. In orally infected laboratory rats and hamsters, fourth-stage larvae were obtained from the stomach at 2–5 days postinfection (p.i.), but no adult worms developed. Larvae introduced surgically into the body cavity of laboratory rats yielded some adult worms from day 42 onwards. Adult males were identified asContracaecum osculatum.     

Serological and Molecular Evidence of Human Granulocytic Ehrlichiosis Focus in the Białowieża Primeval Forest (Puszcza Białowieska), Northeastern Poland

Human granulocytic ehrlichiosis (HGE) is an emerging tickborne zoonosis. First described in the USA, it is being increasingly reported from several European countries. This study was undertaken to provide serological and molecular evidence of the occurrence of the HGE focus in the Białowieża Primeval Forest, located in northeastern Poland. To this end, the seroprevalence of HGE in this area, where Lyme borreliosis and tickborne encephalitis are highly endemic, was determined by means of an indirect immunofluorescence antibody assay. In addition, the frequency of granulocytic Ehrlichia spp. infection in Ixodes ricinus ticks from the same area was estimated using a polymerase chain reaction method with EHR 521 and EHR 747 primers, which amplified a fragment of 16S rDNA. The rate of seropositivity for HGE was 6.2% (8/130 subjects). Individuals seropositive for Lyme borreliosis were more likely to have anti-HGE antibodies than seronegative ones (P<0.05; OR=6.34, 95%CI=1.12–36.98). There was no association between self-reported frequency of tick bites or forestry employment and HGE seropositivity. Sixty of 376 (16%) Ixodes ricinus ticks tested were positive for the Ehrlichia phagocytophila genogroup by polymerase chain reaction. Ehrlichial DNA was present in 59 of 302 (19.5%) adult ticks and in 1 of 74 nymphs (1.4%). There was a significantly higher infection rate among female ticks (32.9%; 49/149) than among male ticks (6.5%; 10/153) (P<0.05). Dual infection with Ehrlichia spp. and Borrelia burgdorferi sensu lato was detected in 10 samples that were positive for ehrlichiae. The results obtained confirm the perpetuation of the HGE agent in the primeval forest ecosystem of northeastern Poland. Electronic Publication