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Factors involved in initiation of infection by Lymantria dispar nuclear polyhedrosis virus
Abstract
The present research provides the first evidence for specific receptor binding of polyhedra-derived baculovirus (PDV) to host cells and to lepidopteran brush border membrane vesicles (BBMV) and demonstration of entry via a non-endocytotic pathway involving direct membrane fusion. The technique of fluorescence-activated cell sorting (FACS) analysis was employed to investigate the specificity of binding between the PDV phenotype of Lymantria dispar multicapsid nuclear polyhedrosis virus (LdMNPV) and host membranes. Fluorescein-labeled PDV was found to bind in a saturable manner to the gypsy moth cell line, IPLB-LdEIta, and to L. dispar BBMV. Excess levels of unlabeled PDV were highly efficient in competing with FITC-labeled PDV for limited receptor sites further supporting the specificity of the interaction. Major reductions in virus binding (as high as 70%) after protease treatment of cells indicated that a protein receptor is involved. A fluorescence dequenching assay of membrane fusion with octadecyl rhodamine B (R18)-labeled PDV as used to identify PDV fusion to host cells and BBMV. Fusion of PDV occurred at 27$\sp\circ$C to both target membranes, as well as at 4$\sp\circ$C at approximately 55% of the levels achieved at 27$\sp\circ$C. Virus fusion to BBMV occurred throughout the pH range of 4-11 with dramatically increased fusion levels (3x) under the alkaline conditions normal for lepidopteran larval midguts. Treatment of tissue cells with chloroquine, a lysosomotropic agent, did not significantly affect PDV fusion to cells or infectivity in tissue culture. To begin to characterize viral and host proteins involved in establishment of infection, monoclonal antibodies (MAbs) were produced against LdMNPV PDV as well as L. dispar BBMV. While no PDV-neutralizing MAbs were isolated, anti-BBMV MAbs were identified which appeared to alter either PDV fusion or infectivity. To determine whether LdMNPV occlusion bodies (OBs) may contain a soluble enhancing factor similar to that identified for several granulosis viruses, soluble LdMNPV OB proteins were tested in larval bioassays for enhancement of PDV infectivity and assayed for the ability to degrade L. dispar peritrophic membrane proteins. Soluble LdMNPV OB proteins were unable to enhance LdMNPV infectivity and did not degrade larval PM proteins.
Subject Area
Microbiology|Entomology
Recommended Citation
Horton, Holly Martha, "Factors involved in initiation of infection by Lymantria dispar nuclear polyhedrosis virus" (1993). Doctoral Dissertations Available from Proquest. AAI9316662.
https://scholarworks.umass.edu/dissertations/AAI9316662