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At least 289 records · Page 16Linked to original sources
PubMed2005

Selective enhancement of the type 1 cytokine response by expression of a canine interleukin (IL)-12 fused heterodimeric DNA.

Interleukin-12 (IL-12) is a heterodimeric cytokine that is a principal mediator of the innate immune response and modulator of acquired cell-mediated immunity. Administration of exogenous IL-12 can direct the host adaptive T cell response toward a type 1 phenotype. The co-administration of IL-12 with vaccine antigens has been shown to augment the vaccine-induced T(H)1 response and protection against intracellular pathogens. We show here that a canine IL-12 DNA, constructed by fusing the p35 and p40 subunit cDNAs with an interspacing linker, generated stable IL-12 transcripts when placed under control of a strong constitutive promoter. The protein expressed from this fused cDNA was fully functional in promoting a type 1 (IFN-gamma) and suppressing a type 2 (IL-4) cytokine response following both in vitro transfection of a canine cell line and in vivo delivery to dogs. This DNA construct may be useful as an adjuvant for vaccines that target tumors or intracellular pathogens of the dog.

Animals↗
PubMed2005

Microarray analysis of Haemophilus parasuis gene expression under in vitro growth conditions mimicking the in vivo environment.

Haemophilus parasuis is the causative agent of polyserositis in pigs, a mostly fatal disease on the rise especially in early-weaned pigs and in pig herds with a high-health status. The mechanisms by which H. parasuis propagates through the body and colonizes the serous membranes are unknown. We have used an H. parasuis microarray to identify virulence genes involved in host adaptation. H. parasuis gene expression was analysed under in vitro growth conditions mimicking the environmental conditions encountered during an infection. These included iron-limitation, acidic and temperature stress and growth under microaerobic conditions. A kinetic impression of the gene regulation was obtained by analysing the transcription 10, 30 and 60 min after induction of the altered growth conditions. A total of 75 regulated H. parasuis genes were identified, most of which coded for transporters of iron and sugar metabolites, metabolic enzymes, DNA metabolism and hypothetical proteins with unknown functions. Furthermore, H. parasuis genes were identified that have homology to known virulence factors in other pathogenic bacteria. Homologues of some of the identified H. parasuis genes are known to be expressed during natural and experimental infections in pathogens of the Pasteurellaceae family.

Bacterial Proteins↗
PubMed2006

Antigenic variation as an exploitable weakness of babesial parasites.

Babesia bovis and its bovine host interact in many ways, resulting in a range of disease and infection phenotypes. Host responses to the parasite elicit or select for a variety of responses on the part of the parasite, the full range of which is not yet known. One well-established phenomenon, thought to aid parasite survival by evasion of host adaptive immune responses, is the sequential expansion of antigenically variant populations during an infection, a phenomenon referred to as "antigenic variation". Antigenic variation in B. bovis, like that in the human malarial parasite, Plasmodium falciparum, is intimately linked to a second survival mechanism, cytoadhesion. In cytoadhesion, mature parasite-containing erythrocytes bind to the capillary and post-capillary venous endothelium through parasite-derived ligands. The reliance of these parasites on both functions, and on their linkage, may provide opportunities to develop anti-babesial and, perhaps, anti-malarial protection strategies. The development of inhibitors of DNA metabolism in B. bovis may be used to abrogate the process of antigenic variation, whereas small molecular mimics may provide the means to vaccinate against a wide range of variants or to prevent the surface export of variant antigen ligands. In this article, aspects of antigenic variation and cytoadhesion in bovine babesiosis are explored, with a discussion of opportunities for prophylactic or therapeutic intervention in these intertwined processes.

Animals↗
PubMed2006

Wide geographic distribution of Cryptosporidium bovis and the deer-like genotype in bovines.

Recent studies in the United States reported that approximately 85% of pre-weaned dairy calves were infected with zoonotic Cryptosporidium parvum, whereas only 1-2% of post-weaned calves and 1-2-year-old heifers were infected with this species. Cryptosporidium bovis and Cryptosporidium deer-like genotype were much more prevalent in the post-weaned animals. It is not clear whether the same infection pattern also occurs in other geographic areas. In this study, to determine whether the same Cryptosporidium infection pattern was present in other geographic areas, we genotyped Cryptosporidium specimens collected from two farms in China and India, using specimens from farms in Georgia, USA for comparison. C. bovis was the most common species found in pre- and post-weaned calves in all three areas. In Georgia, the deer-like genotype was found frequently in pre- and post-weaned calves and Cryptosporidium andersoni was found in one post-weaned calf. Both C. bovis and the deer-like genotype were found in the few milking cows examined in Georgia. There were no differences in the small subunit rRNA gene sequences obtained from C. bovis or deer-like genotype among the three areas. One adult yak in China, however, was infected with a species similar to C. bovis, with only three nucleotide mutations in the target gene. All four common bovine Cryptosporidium spp. were differentiated from each other by restriction fragment length polymorphism analysis of PCR products with enzymes SspI and MboII. Thus, both C. bovis and the deer-like genotype are found in all age groups of cattle in diverse geographic areas and host adaptation of C. bovis might have occurred in yaks.

Age Factors↗
PubMed2004

Strain-specific rate of shutdown of CMV enhancer activity in murine liver confirmed by use of persistent [E1(-), E2b(-)] adenoviral vectors.

The systemic delivery of [E1(-)] adenoviral (Ad) vectors encoding a transgene results in efficient viral uptake and abundant transgene expression in the liver. However, [E1(-)]Ad vector persistence is transient due to cytotoxic T lymphocyte (CTL)-mediated loss of the Ad-infected cells. Our laboratory has previously demonstrated that additional modifications to the [E1(-)]Ad vector genome, by deletion of the Ad E2b genes, significantly decreased virus-genome-derived gene expression and simultaneously improved the long-term performance of the resultant [E1(-), E2b(-)]Ad vector. In this study, we confirmed that [E1(-), E2b(-)]Ad vector genomes could persist equally well in C57Bl/6 or Balb/c mouse hepatocytes. Despite vector genome persistence, we observed a strain-dependent variability in the duration of CMV enhancer/promoter-driven transgene expression in the liver. While Balb/c mice rapidly shut down [E1(-), E2b(-)]Ad-derived transgene expression, C57Bl/6 mice allowed for prolonged transgene expression. This occurred even when both strains were crossed into a severe combined immune-deficient background, demonstrating that host adaptive immune responses are not responsible for the phenomenon. Furthermore, differential methylation of the CMV enhancer/promoter was also not demonstrated in either strain of mouse, eliminating this mechanism as causative. Thus, alternative mechanisms for this phenomenon are discussed.

Adenoviridae↗
PubMed2005

A map of the diversity of RNA3 recombinants appearing in plants infected with Cucumber mosaic virus and Tomato aspermy virus.

In order to better understand the role of recombination in creating the diversity of viral genomes that is acted on by selection, we have studied in detail the population of recombinant RNA3 molecules occurring in tobacco plants coinfected with wild-type strains of cucumber mosaic virus (CMV) and tomato aspermy virus (TAV) under conditions of minimal selection pressure. Recombinant RNA3s were observed in 9.6% of the samples. Precise homologous recombination predominated since it was observed at 28 different sites, primarily in six hot spots. Imprecise homologous recombination was observed at two sites, particularly within a GU repeat in the 5' noncoding region. Seven of the eight aberrant homologous recombination sites observed were clustered in the 3' noncoding region. These results have implications on the role of recombination in host adaptation and virus evolution. They also provide essential baseline information for understanding the potential epidemiological impact of recombination in transgenic plants expressing viral sequences.

Base Sequence↗
PubMed2006

Linking patterns and processes of species diversification in the cone flies Strobilomyia (Diptera: Anthomyiidae).

Phytophagous insects provide useful models for the study of ecological speciation. Much attention has been paid to host shifts, whereas situations where closely related lineages of insects use the same plant during different time periods have been relatively neglected in previous studies of insect diversification. Flies of the genus Strobilomyia are major pests of conifers in Eurasia and North America. They are specialized feeders in cones and seeds of Abies (fir), Larix (larch) ,and Picea (spruce). This close association is accompanied by a large number of sympatric Strobilomyia species coexisting within each tree genus. We constructed a molecular phylogeny with a 1320 base-pair fragment of mitochondrial DNA that demonstrated contrasting patterns of speciation in larch cone flies, as opposed to spruce and fir cone flies; this despite their comparable geographic distributions and similar resource quality of the host. Species diversity is the highest on larch, and speciation is primarily driven by within-host phenological shifts, followed by allopatric speciation during geographical expansion. By contrast, fewer species exploit spruce and fir, and within-host phenological shifts did not occur. This study illustrates within-host adaptive radiation through phenological shifts, a neglected mode of sympatric speciation.

Animals↗
PubMedDate not supplied

Current perspectives in salmonellosis.

Salmonellosis remains an important human and animal problem worldwide and, despite extensive research effort, many of the details of its pathogenesis are not known. While there have been recent advances in some aspects of pathogenesis, other areas are not understood. The host adaptation shown by several serotypes and the recent dramatic changes in the predominance of particular serotypes are examples. Molecular techniques using in vitro model systems have identified several genes involved in adhesion and invasion, though their function and even their relevance to disease remain poorly defined. Similarly, several potential toxins have been identified and the genes cloned, although their significance is far from clear. Some of the essential genes on the large virulence plasmids have been defined, and these are known to be necessary for the establishment of systemic infection. Two of these genes are regulatory, but the function of the other genes is unknown. A general theme has been the identification of gene systems involved in regulation of virulence. New vaccines, based on 'rational attenuation' are being designed, and these have also been used to carry heterologous antigens; such vaccines are currently undergoing trials. The improved understanding of the pathogenesis of salmonellosis may also provide a model of wide applicability to a more general understanding of bacterial pathogenesis. New techniques, including the polymerase chain reaction, are being applied to diagnose salmonellosis.

Animals↗
PubMed1999

Variation in Cryptosporidium: towards a taxonomic revision of the genus.

Cryptosporidium is an important cause of enteric disease in humans and other animals. Limitations associated with conventional diagnostic methods for cryptosporidiosis based on morphological features, coupled with the difficulty of characterising parasites isolated in the laboratory, have restricted our ability to clearly identify species. The application of sensitive molecular approaches has obviated the necessity for laboratory amplification. Such studies have found considerable evidence of genetic heterogeneity among isolates of Cryptosporidium from different species of vertebrate, and there is now mounting evidence suggesting that a series of host-adapted genotypes/strains/species of the parasite exist. In this article, studies on the molecular characterisation of Cryptosporidium during the last 5 years are reviewed and put into perspective with the past and present taxonomy of the genus. The predictive value of achieving a sound taxonomy for the genus Cryptosporidium with respect to understanding its epidemiology and transmission and controlling outbreaks of the disease is also discussed.

Animals↗
PubMed1999

Phenotypic diversity in Lewis expression of Helicobacter pylori isolates from the same host.

Populations of Helicobacter pylori cells show a stable expression of Lewis surface antigens, although phase variation may occur among individual organisms grown in vitro. We searched for variation in Lewis phenotypes among H. pylori cells of minimally in vitro-passaged isolates. Lewis expression in 180 clonal H. pylori populations from the primary culture of 20 gastric biopsy samples from 12 patients, and that in 160 isolates from primary cultures from 16 experimentally infected rodents, were examined by enzyme immunoassays. Substantial differences in Lewis expression were found among the isolates from 9 (75%) of 12 patients. These differences were unrelated to overall genetic diversity as determined by polymerase chain reactions for random amplified polymorphic DNA or cagA status, and they persisted during subsequent in vitro passage. In contrast, Lewis expression was highly uniform in H. pylori isolates from different rodents infected for up to 20 weeks. Variation in H. pylori Lewis expression in genetically closely related organisms in human subjects may provide a pool of bacterial phenotypes for the continuous selection of optimally host-adapted populations suitable for persistence.

Animals↗
PubMed2001

Gamma/delta T cell response of chickens after oral administration of attenuated and non-attenuated Salmonella typhimurium strains.

Poultry represents an important source of Salmonella infection in man. Despite intensive research on immunity, little is known about the involvement of T cell sub-populations in the immunological response of chickens against infection with non-host-adapted Salmonella (S.) serovars. In this study, the T cell composition of blood lymphocytes (CD4(+)CD8(+); CD4(+)CD8(-); CD4(-)CD8(+); CD8(+)TcR1(+); CD8(-)TcR1(+), CD8(+)TcR1(-)) after oral administration of the non-attenuated S. typhimurium wild-type strain 421 (infection) or the attenuated vaccine strain Salmonella vac((R)) T (immunization) to day-old chicks was investigated and compared with non-treated chickens by flow cytofluorometry. Additionally, the occurrence of T cell sub-populations (CD4(+); CD8(+); TcR1(+)(gammadelta); TcR2(+)(alphabeta(1))) in ceca, spleen and bursa of Fabricius of the birds was studied immunohistologically. Blood samples and tissues were examined between days 1 and 12 of age. Chicks inoculated with S. typhimurium 421 or Salmonella vac((R)) T showed significantly elevated percentages of CD8(+)TcR1(+) in blood on days 7, 8 and 9, or on day 8 in comparison to control animals. The CD4 to CD8 cell ratio was about 3:1 in infected animals on day 5 of age. In the organs of treated chicks the numbers of CD8(+)(gammadelta) and TcR1(+)(gammadelta) cells had markedly increased on days 4 and 5 in ceca, 8 and 9 in the bursa and 9 and 12 in the spleen. Moreover, infected or vaccinated birds revealed larger quantities of CD4(+) and TcR2(+) T cells in ceca on days 4 and 5. As shown by double staining, the TcR1(+) cells in the organs of infected animals additionally carried the CD8 antigen. In conclusion, immunization of day-old chicks with the attenuated Salmonella live vaccine strain resulted in the same changes in T cell composition as seen after infection with the non-attenuated Salmonella wild-type strain, but at a lower level. The remarkable increase of CD8(+)TcR1(+)(gammadelta) double positive cells in treated birds indicates an important role of this cell sub-population in the immunological defense of chickens against Salmonella exposure.

Animals↗
PubMed2002

The architecture of variant surface glycoprotein gene expression sites in Trypanosoma brucei.

Trypanosoma brucei evades the immune system by switching between Variant Surface Glycoprotein (VSG) genes. The active VSG gene is transcribed in one of approximately 20 telomeric expression sites (ESs). It has been postulated that ES polymorphism plays a role in host adaptation. To gain more insight into ES architecture, we have determined the complete sequence of Bacterial Artificial Chromosomes (BACs) containing DNA from three ESs and their flanking regions. There was variation in the order and number of ES-associated genes (ESAGs). ESAGs 6 and 7, encoding transferrin receptor subunits, are the only ESAGs with functional copies in every ES that has been sequenced until now. A BAC clone containing the VO2 ES sequences comprised approximately half of a 330 kb 'intermediate' chromosome. The extensive similarity between this intermediate chromosome and the left telomere of T. brucei 927 chromosome I, suggests that this previously uncharacterised intermediate size class of chromosomes could have arisen from breakage of megabase chromosomes. Unexpected conservation of sequences, including pseudogenes, indicates that the multiple ESs could have arisen through a relatively recent amplification of a single ES.

Animals↗
PubMed2001

Passive immunization with Neisseria meningitidis PorA specific immune sera reduces nasopharyngeal colonization of group B meningococcus in an infant rat nasal challenge model.

To examine the protective efficacy of specific immune sera generated by meningococcal vaccine candidates against nasopharyngeal colonization, we developed an infant rat nasal colonization model for group B meningococcus. In this model, Sprague-Dawley infant rats were challenged intranasally in with host adapted, piliated Neisseria meningitidis group B strains H355 or H44/76 administered concurrently with iron dextran. Colonization was assessed by quantitative culture of nasal homogenates and expressed as log(10) colony forming units (c.f.u.) per nose. Three to five log(10) c.f.u. of N. meningitidis were routinely recovered from the nasal tissue up to 4 days post-challenge. Passive immunization (i.p.) of the infant rats with either PorA or whole cell antisera 24 h prior to homologous challenge resulted in a significant reduction of N. meningitidis colonization in the nasal tissues of these animals. These results demonstrate that this model can be utilized to evaluate the role of antibody to prevent the initial nasopharyngeal colonization by group B meningococcus.

Administration, Intranasal↗
PubMed1999

Transmission trials, ITS2-PCR and RAPD-PCR show identity of Toxocara canis isolates from red fox and dog.

Toxocara canis isolates from dog and from red fox were compared in transmission trials and with molecular analysis using RAPD-PCR technique and comparison of the ITS2 sequence. After oral infection of bitches with 20,000 embryonated T. canis eggs of vulpine and canine origin, the vertical transmission to pup's was examined. All animals of both groups developed typical clinical symptoms of toxocarosis. The haematological, serological, parasitological and post mortem results showed no differences between both isolates except for the infectivity of T. canis stages in mice where the fox isolate showed a significant higher infectivity than the dog isolate. The RAPD-PCR showed a similarity coefficient of 0.95, similar to the range of intraspecific variation in Toxocara cati and Toxascaris leonina specimens as outgroups. The ITS2 comparison showed a 100% identity between both isolates with no intraspecific variations. Therefore, the study shows that the fox and the dog isolate of T. canis were identical in infectivity, transmission and molecular structure; a host adaptation could not be found and the fox has to be seen as a reservoir for T. canis infections in dogs. Considering the increasing number of foxes in urban areas the importance of helminth control in dogs is stressed.

Animals↗
PubMed2000

Structural features of the avian influenza virus hemagglutinin that influence virulence.

Analysis of the structure of the avian influenza (AI) virus hemagglutinin (HA) gene and protein has yielded a wealth of information on the virulence mechanisms of influenza viruses. The AI hemagglutinin appears to be unique in its capacity to accept basic amino acids at its proteolytic cleavage site (PCS). The association of multiple basic (MB) amino acids, HA cleavage, tissue spread and virulence by AI strains first proposed in the late 1970s and early 1980s [Klenk, H.D., Rott, R., Orlich, M., 1977. J. Gen. Virol. 36, 151-161; Bosch, F.X., Garten, W., Klenk, H.D., Rott, R., 1981. Virology 113, 725-735] has held fast for two decades now. While other structural characteristics and other genes can certainly influence virulence, the presence of MB amino acids at the PCS has provided a hallmark structural feature which justifies continuing sequence analysis of emerging field isolates of AI strains. In addition to this structural feature, the distal tip of the HA is prone to appearance and disappearance of glycosylation sites, some of which have been associated with virulence. The recent outbreaks of highly pathogenic AI in Mexico, Australia, Pakistan, Hong Kong and in the ongoing outbreak of moderately pathogenic H7 avian influenza in the northeast US have all provided new and useful information regarding the role of HA RNA and protein structure in both virulence and host adaptation. We have previously noted that stable RNA secondary structure near the PCS is related to the acquisition of virulence and have proposed that the secondary structure may promote the insertion of basic amino acids. In this report we evaluate the phylogenetic relationships for three recent isolates of highly pathogenic avian influenza viruses and the possible virulence factors associated with their primary and secondary structure.

Glycosylation↗
PubMed1999

Monophasic group B Salmonella species infecting harbour porpoises (Phocoena phocoena) inhabiting Scottish coastal waters.

A monophasic strain of Salmonella group B having the antigenic structure 4, 12: a: - was isolated in culture from various tissues of 39 harbour porpoises (Phocoena phocoena). The tissue from which the organism was recovered most frequently was lung in 33 animals and intestine in 16 animals, but it was also isolated from heart valve, liver, kidney, spleen, mesenteric lymph node, pulmonary lymph node, hepatic lymph node, urethra, sheath and epididymis. As far as we are aware this is the first record of this strain from an animal source, raising the possibility that it may be host-adapted to harbour porpoises. The possible modes of transmission of monophasic group B Salmonella between porpoises are discussed.

Agglutination Tests↗
PubMed1993

Strangles.

The etiology, epizootiology, pathogenesis, and clinical presentation of strangles are described. Streptococcus equi, the causative organism, is highly host-adapted to Equidae and shows no antigenic variation. Protective immunity apparently is mediated by a combination of serum opsonic and nasopharyngeal mucosal humoral responses. Vaccines based on M protein or inactivated bacterial suspensions may reduce the clinical attack rate by 50%, a level of protection much lower than that produced during recovery from strangles.

Animals↗
PubMed2001

Evolutionary trends in the genus Bordetella.

The genus Bordetella comprises seven species with pathogenic potential for different host organisms. This article attempts to review our current knowledge about the systematics and evolution of this important group of pathogens, their relationship to environmental microorganisms and about molecular mechanisms of host adaptation.

Animals↗