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The reverse transcriptase-polymerase chain reaction (RT-PCR) was used to amplify the first part or full capsid gene (VP60) of EBHSV and RHDV. The fragment covered full capsid gene and the most part of gene contained in ORF2 of EBHSV was also obtained. The specificity of PCR products was checked by digestion with restriction enzymes.
Eight Polish strains of European brown hare syndrome virus, isolated in 1992-93, 1998 and 2001, as well as 2 standard strains: French (F/st) and Italian (It/st) were analysed. The fragments of genome, including the capsid protein gene, were amplified by RT-PCR or N-PCR and digested by endonucleases: Xho I, Sst I, BamH I, Sma I, Hpa II and BsuR I. The results of restriction enzyme digestion were compared with restriction maps, obtained after computer analysis of nucleotide sequences of other European strains, available in GenBank. The results of analysis of Polish strains, isolated in different years, revealed the changes in restriction profiles between them and other European strains. The 3 out of 5 Polish strains detected in 1992-93 demonstrated the same restriction profiles, similar to French "GD" strain. The two other strains revealed, for same endonucleases, restriction patterns similar to ltalian "BS89" or German strains. The strains isolated in 1998 and 2001 demonstrated higher differences in restriction profiles in comparison with Polish and other European strains previously detected. These changes in nucleotide scquences of the part of genome studied, indicate the diversity of EBHSV.
The 18 RHDV strains, isolated between 1993 and 2005 in Poland, as well as one standard strain were used in these studies. The RT-PCR technique was carried out in order to amplify the 538 bp fragment located in the variable region of gene encoding capsid protein (VP60). The phylogenetic analysis of nucleotide sequences of 18 Polish and 25 foreign strains revealed that Polish strains were clustered to 4 genogroups. One of them from 1993 was grouped together with old European strains isolated between 1987 and 1990. Thirteen strains isolated between 1994 and 2004, as well as two strains isolated in 1994 and 1996, were clustered to two separate genetic groups. Two strains detected in 2004 and 2005, were located in genogroup of antigenic variants. The maximum nucleotide divergence among Polish strains (10.3%) was found between strain isolated in 1996 and antigenic variants. The alignment of deduced amino acid sequences of the VP60 confirmed the localisation of 2 Polish strains in genetic group of antigenic variants. The identical amino acid substitutions in the same positions, like in other antigenic variants, were observed. The relation between antigenic properties and genetic variations of strains was taken under consideration.
Rabbit hemorrhagic disease virus (RHDV) which causes a highly contagious disease of wild and domestic rabbits belongs to the family Caliciviridae. It is a small, positive single-stranded RNA virus with a genome of 7.5 kb and has a diameter of approximately 40 nm. In negatively stained electron micrographs the virus shows typical calicivirus morphology with regularly arranged cup-shaped structures on the surface. It is a major pathogen of rabbits in many countries. Vp60 - a coat protein of molecular mass around 60 kDa is the major antigen of RHDV. It is present as 90 dimeric units per virion particle. We have expressed VP60 gene in the baculovirus system with the aim to use it as a potential vaccine against RHDV and a diagnostic reagent in immunological tests. cDNA of the vp60 gene of strain SGM, was cloned into a baculovirus transfer vector as full-length gene, as well as truncated gene lacking 600 5'-terminal nucleotides. The sequence of SGM VP60 differed markedly from that of the reference strain. Full-length recombinant VP60 protein from the SGM strain self-assembled to form virus-like particles (VLPs). These particles observed by electron microscopy were morphologically similar to native virions and were able to agglutinate human group 0 erythrocytes. After immunization the recombinant particles induced RHDV-specific antibodies in rabbits and guinea pigs. Rabbits immunized with the VLPs were fully protected against challenge with a virulent RHDV.
Changes in the number of T and B lymphocytes and their subpopulations (Th, Tc/Ts, cells with CD25+ receptor) in peripheral blood of rabbits experimentally infected with one of two Czech strains (CAMPV-351 and CAMPV-561) of RHD virus were studied. The lymphocytes were identified using a cytometer and monoclonal antibodies directed against CD5+ (at T lymphocytes), CD4+ (at Th lymphocytes), CD8+ (at Tc/Ts lymphocytes), CD25, or IgM receptor at B lymphocytes. In addition, disease symptoms were recorded in the infected rabbits and their mortality was monitored. Analysis of the results showed that the examined strains induced a distinct immune response of the lymphocytes and that the response was more pronounced following the infection with the CAMPV-561 strain. The recorded changes were expressed more frequently by an increased than decreased percentages of the examined lymphocytes. The mortality was variable and reached 30% in animals infected with the CAMPV-351 strain and 75% in animals infected with the CAMPV-561 strain.
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