The Experts below are selected from a list of 2922 Experts worldwide ranked by ideXlab platform
John Colvin - One of the best experts on this subject based on the ideXlab platform.
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mathematical models of host plant infection by Helper Dependent Virus complexes why are Helper Viruses always avirulent
Phytopathology, 2000Co-Authors: Xusheng Zhang, J Holt, John ColvinAbstract:ABSTRACT Interactions between Viruses in plants are common, and some Viruses depend on such interactions for their survival. Frequently, a Virus lacks some essential molecular function that another provides. In "Helper-Dependent" Virus complexes, the Helper Virus is transmitted inDependently by a vector, whereas the Dependent Virus depends on molecular agents associated with the Helper Virus for transmission by a vector. A general mathematical model was developed of the dynamics of host plant infection by a Helper-Dependent Virus complex. Four categories of host plants were considered: healthy, infected with Helper Virus alone, infected with Dependent Virus alone, and infected with both Viruses. New planting of the host crop was constrained by a maximum abundance due to limitation of the cropping area. The ratio of infection rate to host loss rate due to infection is proposed as an important epidemiological quantity, A, that can be used as a measure of the mutual adaptation of the Virus and host. A number of alternative equilibria of host infection could occur and were determined exclusively by parameter values; it was informative to display their distribution in the parameter plane: (1/A)(Helper) versus (1/A)(Dependent). A simple analysis of the distribution of the final equilibria illustrated that the Dependent Virus could affect the survival of the Helper Virus, so facilitation between the two can be reciprocal. The distribution of the final equilibria also indicated that a well-adapted Helper Virus increases the opportunity for a Dependent Virus to evolve and survive, and the model, therefore, explains why infection with a Helper Virus usually causes no or little damage to plants, whereas infection with a Dependent Virus or mixed infection with both often causes very severe damage.
Xusheng Zhang - One of the best experts on this subject based on the ideXlab platform.
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mathematical models of host plant infection by Helper Dependent Virus complexes why are Helper Viruses always avirulent
Phytopathology, 2000Co-Authors: Xusheng Zhang, J Holt, John ColvinAbstract:ABSTRACT Interactions between Viruses in plants are common, and some Viruses depend on such interactions for their survival. Frequently, a Virus lacks some essential molecular function that another provides. In "Helper-Dependent" Virus complexes, the Helper Virus is transmitted inDependently by a vector, whereas the Dependent Virus depends on molecular agents associated with the Helper Virus for transmission by a vector. A general mathematical model was developed of the dynamics of host plant infection by a Helper-Dependent Virus complex. Four categories of host plants were considered: healthy, infected with Helper Virus alone, infected with Dependent Virus alone, and infected with both Viruses. New planting of the host crop was constrained by a maximum abundance due to limitation of the cropping area. The ratio of infection rate to host loss rate due to infection is proposed as an important epidemiological quantity, A, that can be used as a measure of the mutual adaptation of the Virus and host. A number of alternative equilibria of host infection could occur and were determined exclusively by parameter values; it was informative to display their distribution in the parameter plane: (1/A)(Helper) versus (1/A)(Dependent). A simple analysis of the distribution of the final equilibria illustrated that the Dependent Virus could affect the survival of the Helper Virus, so facilitation between the two can be reciprocal. The distribution of the final equilibria also indicated that a well-adapted Helper Virus increases the opportunity for a Dependent Virus to evolve and survive, and the model, therefore, explains why infection with a Helper Virus usually causes no or little damage to plants, whereas infection with a Dependent Virus or mixed infection with both often causes very severe damage.
J Holt - One of the best experts on this subject based on the ideXlab platform.
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mathematical models of host plant infection by Helper Dependent Virus complexes why are Helper Viruses always avirulent
Phytopathology, 2000Co-Authors: Xusheng Zhang, J Holt, John ColvinAbstract:ABSTRACT Interactions between Viruses in plants are common, and some Viruses depend on such interactions for their survival. Frequently, a Virus lacks some essential molecular function that another provides. In "Helper-Dependent" Virus complexes, the Helper Virus is transmitted inDependently by a vector, whereas the Dependent Virus depends on molecular agents associated with the Helper Virus for transmission by a vector. A general mathematical model was developed of the dynamics of host plant infection by a Helper-Dependent Virus complex. Four categories of host plants were considered: healthy, infected with Helper Virus alone, infected with Dependent Virus alone, and infected with both Viruses. New planting of the host crop was constrained by a maximum abundance due to limitation of the cropping area. The ratio of infection rate to host loss rate due to infection is proposed as an important epidemiological quantity, A, that can be used as a measure of the mutual adaptation of the Virus and host. A number of alternative equilibria of host infection could occur and were determined exclusively by parameter values; it was informative to display their distribution in the parameter plane: (1/A)(Helper) versus (1/A)(Dependent). A simple analysis of the distribution of the final equilibria illustrated that the Dependent Virus could affect the survival of the Helper Virus, so facilitation between the two can be reciprocal. The distribution of the final equilibria also indicated that a well-adapted Helper Virus increases the opportunity for a Dependent Virus to evolve and survive, and the model, therefore, explains why infection with a Helper Virus usually causes no or little damage to plants, whereas infection with a Dependent Virus or mixed infection with both often causes very severe damage.
Amine Kamen - One of the best experts on this subject based on the ideXlab platform.
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an efficient process for the purification of Helper Dependent adenoviral vector and removal of Helper Virus by iodixanol ultracentrifugation
Journal of Virological Methods, 2010Co-Authors: Edwige Dormond, Parminder Chahal, Alice Bernier, Rosa Tran, Michel Perrier, Amine KamenAbstract:The preparation of large amount of purified Helper-Dependent adenoviral vector material is hampered by the lack of development of downstream processes with proven records on separation and recovery efficiencies. In order to facilitate the use of clinical-grade Helper-Dependent Virus material for large-scale in vivo studies, a three-step purification scheme consisting of (1) an anion-exchange chromatography for initial capturing of Virus, (2) a shallow iodixanol density gradient ultracentrifugation for the removal of Helper Virus from Helper-Dependent Virus, and (3) a size-exclusion chromatography for the removal of iodixanol and residual protein contaminants as a polishing step was developed. The use of a fast iodixanol density ultracentrifugation step was highly effective in separating infectious Helper-Dependent Virus from contaminating Helper Virus. The overall downstream processing scheme gave 80% infectious particle yield. The contamination ratio of Helper Virus in the Helper-Dependent Virus preparation are reduced from 2.57 to 0.03% corresponding to a reduction of Helper Virus by factors of 85 by two iodixanol purification steps. It was also demonstrated that size-exclusion chromatography is an excellent step for the removal of iodixanol and polishing of the final Helper-Dependent Virus preparation.
Edwige Dormond - One of the best experts on this subject based on the ideXlab platform.
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an efficient process for the purification of Helper Dependent adenoviral vector and removal of Helper Virus by iodixanol ultracentrifugation
Journal of Virological Methods, 2010Co-Authors: Edwige Dormond, Parminder Chahal, Alice Bernier, Rosa Tran, Michel Perrier, Amine KamenAbstract:The preparation of large amount of purified Helper-Dependent adenoviral vector material is hampered by the lack of development of downstream processes with proven records on separation and recovery efficiencies. In order to facilitate the use of clinical-grade Helper-Dependent Virus material for large-scale in vivo studies, a three-step purification scheme consisting of (1) an anion-exchange chromatography for initial capturing of Virus, (2) a shallow iodixanol density gradient ultracentrifugation for the removal of Helper Virus from Helper-Dependent Virus, and (3) a size-exclusion chromatography for the removal of iodixanol and residual protein contaminants as a polishing step was developed. The use of a fast iodixanol density ultracentrifugation step was highly effective in separating infectious Helper-Dependent Virus from contaminating Helper Virus. The overall downstream processing scheme gave 80% infectious particle yield. The contamination ratio of Helper Virus in the Helper-Dependent Virus preparation are reduced from 2.57 to 0.03% corresponding to a reduction of Helper Virus by factors of 85 by two iodixanol purification steps. It was also demonstrated that size-exclusion chromatography is an excellent step for the removal of iodixanol and polishing of the final Helper-Dependent Virus preparation.