Listera ovata

Lectins The mannose-specific plant lectins from Galanthus, Hippeastrum, Narcissus, Epipactis helleborine, and Listera ovata, and the V-acctylglucosaminc-spccilic lectin from Urtica dioica would primarily be targeted at the virus-cell fusion process. 

A number of mannose-specific agglutinines (lectins) from Galanthus nivalis, Hippeastrum hybrid, Narcissus pseudonarcissus, Listera ovata, Cymbidium hybrid, Epipactis helleborine, and the N-acetylglucosamine-specific lectin from Urtica dioica have been found to inhibit HIV-1 and HIV-2 infection at similar concentrations as dextran sulfate (IC50 0.2 to 0.6 fig/ml), or even lower (IC50 0.04 to 0.08 pg/ml. Akin to sulfated polysaccharides, the plant lectins also exhibit activity against various enveloped viruses other than HIV, i.e., HSV-1, HSV-2, CMV, RSV, and influenza virus. Plant lectins would primarily interfere with the virus-cell fusion process. Their precise mode of action remains to be resolved. 

It will be noted that the snowdrop lectin (GNA) is specific for Man(al-3)Man linkages and exhibits high affinity for the branched trisaccharide Man(al-3)[Man(al-6)]Man [104,110] the daffodil lectin (NPA) for a-1,3- and a-l,6-linked mannose disaccharides [105] the amaryllis lectin (HHA) for a-l,6-linked mannose oligosaecharides [105] and the garlic (ASA) and ramsons (AUA) lectins for Man(al-3)Man units [106]. Similar to the snowdrop lectin, the orchid lectin Listera ovata) is highly specific for a-1,3-mannose oligomers [109]. 

PS from terrestrial plants have also been reported as anti-CMV agents. For example, PS from three plant species, Astragalus brachycentrus D. C., Astragalus echidnaeformis Sirjaev and Sterculia urens Roxb., which are devoid of in vitro antiviral activity, were evaluated in mouse models of murine CMV infections [109], Treatment with the compounds needed to be started one day prior to virus inoculation for maximum protective benefit. Treatments starting after virus inoculation were ineffective. The mannose-specific plant PS from the orchid species Cymbidium hybrid Cym., Epipactis helleborine (L) Crantz. and Listera ovata (L.) R.Br. Svenska are potent and selective inhibitors of human CMV in vitro [110], They presumably interact at the level of virion fusion with the target cell. 

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