title: Identification and characterization of a monoclonal antibody recognizing a galactose-binding domain of the toxin ricin.
abstract: A monoclonal antibody raised against purified ricin B chain, 75/3B12, blocked ricin toxicity 30- to 100-fold in vitro. The 75/3B12 IgG and F(ab')2 blocked ricin binding to cell surface galactose-containing receptors. The 75/3B12 Fab bound ricin D with a Ka of 10(7) M-1, and this binding was blocked by asialofetuin, lactose, and N-acetylgalactosamine--molecules which interact with the ricin galactose-binding site--but not by fetuin, sucrose, or glucose. The 75/3B12 Fab contained no detectable carbohydrate and, according to several lines of evidence, did not bind ricin via Ig carbohydrate determinants. The monoclonal antibody appears to recognize a galactose-binding site on ricin D via the variable region of the antibody. The 75/3B12 Fab bound ricin E only 1/50 as well as ricin D and bound the Ricinus agglutinin only 1/80 as well as ricin D. The antibody specificity indicates that structural differences exist in the galactose-binding sites of the Ricinus communis lectins. Abrin and other lectins which bind galactose or N-acetylgalactosamine were not significantly bound by the monoclonal antibody. In vitro, the antibody blocked the nontarget toxicity of immunotoxins similarly to lactose. However, in vivo, unlike lactose, the 75/3B12 antibody protected mice from ricin toxicity.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000918:Antibody Specificity; D001665:Binding Sites; D001667:Binding, Competitive; D000939:Epitopes / Q000276:immunology*; D005690:Galactose / Q000378:metabolism*; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007135:Immunoglobulin Variable Region / Q000276:immunology; D037102:Lectins / Q000276:immunology / Q000378:metabolism; D008214:Lymphocytes / Q000187:drug effects; D051379:Mice; D008807:Mice, Inbred BALB C; D012276:Ricin / Q000276:immunology* / Q000378:metabolism / Q000494:pharmacology
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D007140:Immunoglobulin Fab Fragments; D007135:Immunoglobulin Variable Region; D037102:Lectins; D012276:Ricin; D005690:Galactose