272786 RTA-specific monoclonal antibodies neutralize ricin toxin intracellularly

Monday, October 29, 2012

Joanne O'Hara, MS , Department of Biomedical Sciences, University at Albany, School of Public Health, Rensselaer, NY
Anastasiya Yermakova, BS , Department of Biomedical Sciences, University at Albany, School of Public Health, Rensselaer, NY
Nicholas Mantis, PhD , Department of Biomedical Sciences, University at Albany, School of Public Health, Rensselaer, NY
Antibodies are extraordinary in their capacity to neutralize even the most potent toxins, including botulinum, anthrax, tentanus and ricin toxins. It is generally assumed that antibodies inactivate toxins by either preventing their ability to bind receptors on host cells or by promoting their clearance from circulation via Fc-receptor mediated uptake. In this study, we provide evidence that challenges this paradigm. Although ricin toxin uses its B-subunit (RTB) to bind to cells, the majority of antibodies elicited in response to ricin target its enzymatic A-subunit (RTA). We have recently produced a collection of ricin neutralizing monoclonal antibodies (mAbs) directed against RTA. Using two neutralizing anti-RTA mAbs called R70 and IB2 we showed that neither of them prevented ricin binding to cell surfaces, as measured by flow cytometry. R70 retained toxin neutralizing activity in a Vero cell cytotoxicity assay when added after ricin had attached to cell surfaces. Colocalization of both mAbs with ricin was detected intracellularly in Vero cells by confocal microscopy. Interestingly, in vitro assays that mimic specific steps in the intracellular trafficking of ricin demonstrated that IB2 affected the ability of protein disulfide isomerase to reduce the disulphide bond linking RTA to RTB. Furthermore IB2 interfered with RTA's capacity to arrest protein synthesis. In conclusion these results suggest that RTA-specific mAbs neutralize ricin intracellularly. These findings will have implications for toxin vaccine design as well as contribute to our fundamental understanding of how antibodies neutralize ricin as well as other medically relevant AB toxins.

Learning Areas:
Basic medical science applied in public health
Public health or related research

Learning Objectives:
Identify the mechanism of immunity to ricin toxin to enable the design and development of more effective toxin vaccines and therapeutics.

Keywords: Bioterrorism, Disease Prevention

Presenting author's disclosure statement:

Qualified on the content I am responsible for because: The study described in the abstract reflects part of my PhD dissertation work. I have been studying immunity to ricin for the past four years under the mentorship of Dr. Nicholas J. Mantis, who is a reknown expert in ricin immunity.
Any relevant financial relationships? No

I agree to comply with the American Public Health Association Conflict of Interest and Commercial Support Guidelines, and to disclose to the participants any off-label or experimental uses of a commercial product or service discussed in my presentation.

Back to: 3073.0: Delta Omega Poster Session