A Neutralizing Antibody to the A Chain of Abrin Inhibits Abrin Toxicity both In Vitro and In Vivo

Abstract

Plant ribosome-inactivating proteins (RIPs) are RNA N-glycosidases that inhibit protein synthesis in cells. Abrin, a type II RIP, is an AB type toxin, which is one of the most lethal types of toxin known. The B chain facilitates the entry of the molecule into the cell, whereas the A chain exerts the toxic effect. We have generated hybridomas secreting antibodies of the immunoglobulin G class specific to the recombinant A chain of abrin. One monoclonal antibody, namely, D6F10, rescued cells from abrin toxicity. Importantly, the antibody also protected mice from lethal doses of the toxin. The neutralizing effect of the antibody was shown to be due to interference with abrin attachment to the cell surface.Ribosome-inactivating proteins (RIPs) are a family of protein toxins that bring about the inhibition of protein synthesis either directly by inactivating the ribosomes or indirectly by modifying factors involved in translation (27). They are distributed widely in nature and are found in bacteria, fungi, and plants (34). One of the most potent members of the RIP family is abrin produced by the subtropical climber Abrus precatorius (2). Abrin is an AB type toxin with a 30-kDa A chain, an RNA N-glycosidase that irreversibly inactivates the 28S rRNA of the mammalian 60S ribosomal subunit. Once in the cytosol, the A chain depurinates the adenine of the alpha-sarcin-ricin loop and thereby arrests host cell protein synthesis (7,28). The B chain is a galactose-specific lectin and hence binds to cell surface glycosylated receptors, which allows the toxin entry (31, 16). Apart from inhibiting protein synthesis, RIPs induce apoptosis (23). Abrin shows significant similarities to ricin at the sequence level as well as the structural level, but abrin is several times more potent than ricin (28). There is much interest in understanding the bioactivities of these proteins, owing to their extreme toxicity (the 50% lethal dose [LD 50 ] of abrin for mice is 0.04 g/kg of body weight, and the LD 50 of ricin is 3 g/kg) (35), stability, and easy availability. Both proteins cause pulmonary edema, with acute destructive alveolitis and apoptosis and necrosis in the lower respiratory tract epithelium (10, 41). RIPs from different plants are potent elicitors of sensitization and immunoglobulin E (IgE) production (36). The use of these proteins as bioterrorist weapons is also of considerable concern (3, 4, 17). The passive administration of antibodies has proven to be a specific and effective mode of defense against poisoning by various biological toxins (29). Although both anti-A chain and anti-B chain antibodies are able to neutralize toxins in vitro and in vivo, antibodies against the A chain of ricin have better protective efficacy than anti-B chain antibodies (14, 19).While many detection and treatment modalities for ricin toxicity have been developed previously, few methods for the treatment of abrin toxicity are known (3,40,15). No antidote or vaccine for abrin has been described before now. The aim of the present study was to identi...

Antibody treatment against pulmonary exposure to abrin confers significantly higher levels of protection than treatment against ricin intoxication

“…In one study, phage display technology was utilized to select anti-abrin human monoclonal antibodies from a human naïve scFv library (Zhou et al, 2007), however these were not examined in animal models for their therapeutic value. In another study, a monoclonal antibody mapped to abrin A-chain, was found to protect mice from abrin challenge when given 1 h prior to exposure (Surendranath and Karande, 2008).…”

A monoclonal antibody to an abrin chimera recognizing a unique epitope on abrin A chain confers protection from abrin-induced lethality

“…[9][10][11][12] The only known neutralizing monoclonal antibody (mAb) namely D6F10 for abrin was reported from our laboratory. 13 This mAb was found to inhibit the enzymatic activity of the abrin A chain in vitro and also conferred protection to mice in vivo. 13,14 Toward mapping the epitope corresponding to this mAb, at first various overlapping truncated forms of the abrin A chain were constructed and examined for binding to the mAb.…”

“…13 This mAb was found to inhibit the enzymatic activity of the abrin A chain in vitro and also conferred protection to mice in vivo. 13,14 Toward mapping the epitope corresponding to this mAb, at first various overlapping truncated forms of the abrin A chain were constructed and examined for binding to the mAb. We could conclude that the epitope lay in the amino acids 1-123 of ABA.…”

A novel recombinant vaccine protecting mice against abrin intoxication

“…AT shows significant similarities to ricin toxin (RT) at the sequence level as well as the structural level, but it is 75 times more toxic than the latter (the estimated LD 50 of AT in mice is 0.04 mg/kg of body weight, and the LD 50 of RT is 3 mg/kg). 2 In addition, AT can be extracted using a relatively simple and cheap procedure. These characteristics make AT a choice for a suitable assassination weapon or a biological warfare agent .…”

“…3 Toxin poisoning usually can be prevented by vaccination with toxoid, 4,5 or by passive administration with antibodies in experimental animals. 2,6 Both procedures are effective in the prophylaxis or therapy of toxin poisoning in mice. Currently, only vaccines based on a toxoid of AT ( attenuated with formalin as reported by Griffiths 5 ) and A chain subunit ( ATA mutant 1 and truncated ATA 7 ) produced in our lab, were effective in neutralizing intoxication by AT.…”