Hybridoma cells producing antibodies against A-chain of mistletoe lectin I are resistant to this toxin.
The cytotoxic effect of mistletoe lectin I (MLI) on TA5 hybridoma cells which produce monoclonal antibodies (mAb) to MLI A-chain (MLA) was investigated. In vitro cytotoxic tests with colorimetric assay were carried out for LD50 determination. TA5 hybridoma cells were 100 times more resistant to MLI and 30 times to chimeric toxin consisting of MLA and ricin B-chain (MLA/RTB) than control cells. The TA5 mAb (IgG1) recognized MLI A-chain in Western blotting and bound 125I-labeled MLI with Ka of 0.43 x 10(8) M-1. The TA5 and control hybridomas had the same number of 125I-labeled MLI binding sites. Therefore cell-surface TA5 antibodies did not influence MLI binding with the cell. The cytotoxic effect and binding of MLI were completely blocked in the presence of 20 mM lactose. Thus, MLI cytotoxicity was mediated only by cell-surface galactosyl residues; intracellular mAb molecules block MLI toxicity. Our data suggest that MLA molecules mediating cytotoxicity pass through an anti-MLA antibody-containing vesicular compartment and that mAbs inhibit the translocation activity of MLI A-chain from intracellular vesicles into the cytosol.
Tonevitsky
A G
AG
State Scientific Center of Russian Federation Gniigenetika, Moscow.
Shamshiev
A T
AT
Prokoph'ev
S A
SA
Agapov
I I
II
Toptygin AYu
D000818:Animals; D000911:Antibodies, Monoclonal / Q000096:biosynthesis* / Q000737:chemistry; D001666:Binding Sites, Antibody; D006825:Hybridomas / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D037102:Lectins / Q000737:chemistry / Q000276:immunology* / Q000633:toxicity; D051379:Mice; D008807:Mice, Inbred BALB C; D014784:Mistletoe / Q000276:immunology*; D037121:Plant Lectins; D028321:Plant Preparations; D010940:Plant Proteins; D010946:Plants, Medicinal; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000633:toxicity; D054790:Ribosome Inactivating Proteins, Type 2; D012276:Ricin / Q000633:toxicity; D014118:Toxins, Biological / Q000737:chemistry / Q000276:immunology* / Q000633:toxicity
D000911:Antibodies, Monoclonal; D037102:Lectins; D037121:Plant Lectins; D028321:Plant Preparations; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological; C009674:ribosome inactivating protein, Viscum; D012276:Ricin