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  • Title: Identification and characterization of a monoclonal antibody recognizing a galactose-binding domain of the toxin ricin.
    Author: Colombatti M, Johnson VG, Skopicki HA, Fendley B, Lewis MS, Youle RJ.
    Journal: J Immunol; 1987 May 15; 138(10):3339-44. PubMed ID: 2437188.
    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.
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