Recommended Immunological Assays to Screen for Ricin-Containing Samples

Abstract

Ricin, a toxin from the plant Ricinus communis, is one of the most toxic biological agents known. Due to its availability, toxicity, ease of production and absence of curative treatments, ricin has been classified by the Centers for Disease Control and Prevention (CDC) as category B biological weapon and it is scheduled as a List 1 compound in the Chemical Weapons Convention. An international proficiency test (PT) was conducted to evaluate detection and quantification capabilities of 17 expert laboratories. In this exercise one goal was to analyse the laboratories’ capacity to detect and differentiate ricin and the less toxic, but highly homologuous protein R. communis agglutinin (RCA120). Six analytical strategies are presented in this paper based on immunological assays (four immunoenzymatic assays and two immunochromatographic tests). Using these immunological methods “dangerous” samples containing ricin and/or RCA120 were successfully identified. Based on different antibodies used the detection and quantification of ricin and RCA120 was successful. The ricin PT highlighted the performance of different immunological approaches that are exemplarily recommended for highly sensitive and precise quantification of ricin.

Biological toxins of potential bioterrorism risk: Current status of detection and identification technology

“…As a common feature, none of these was able to discriminate ricin unambiguously from RCA120 [16,19,21]. In this context, Stern et al very recently developed a solution to this problem based on immunological methods in combination with surface plasmon resonance [23].…”

“…Alternatively, laboratories using highly sophisticated MSbased methods targeting both protein identity and functional activity of ricin delivered convincing results. Several of the successful approaches have been published elsewhere in more detail [19,22,27].…”

“…As to quantification, mostly ELISA and one quantitative MS approach were used in combination with different in-house calibrants [19,22]. Still, it was possible to determine a consensus concentration on the RM offered in the PT -to our knowledge, this material represents the only thoroughly characterized ricin RM with a consensus concentration defined in an international PT [21].…”

“…For screening purposes, mostly sandwich enzymelinked immunosorbent assays (ELISAs) are being used, detecting the presence of the protein and reaching detection limits from ng/mL to fg/mL depending on the antibodies and the read-out system used [19], where ultrasensitive detection has been obtained by using the proprietary single molecule array technology [20]. A less sensitive, but much faster approach is on-site detection assays such as lateral flow assays (LFA) or biosensor approaches based on different principles and read-outs that usually reach detection limits in the ng/mL range within about 30 min [15].…”

On-site detection of bioterrorism-relevant agents

“…Während mit Labormethoden beispielsweise Toxine im ein-bis zweistelligen Picogramm-pro-Milliliter-Bereich nachgewiesen werden können [19], sind kommerzielle Lateral Flow Assays (LFA) um einen Faktor 1000 weniger empfindlich und benötigen bestenfalls wenige Nanogramm pro Milliliter für den Toxinnachweis [20]. Der Hauptgrund hierfür liegt im direkten Nachweis der Antikör-perbindung, wohingegen bei Labormethoden enzymatische Signalamplifikationsschritte zu einer deutlichen Steigerung der Sensitivität führen [21].…”