The conserved structure of snake venom toxins confers extensive immunological cross-reactivity to toxin-specific antibody R.A. Harrison a, * , W. Wu ¨ster b , R.D.G. Theakston a a Alistair Reid Venom Research Unit, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK b School of Biological Sciences, University of Wales, Bangor LL57 2UW, UK Received 25 September 2002; accepted 4 November 2002 Abstract We have demonstrated previously that antisera from mice immunised with DNA encoding the carboxy-terminal domain (JD9) of a potent haemorrhagic metalloproteinase, jararhagin, neutralised over 70% of the haemorrhagic activity of the whole Bothrops jararaca venom. Here, we demonstrate that the JD9-specific antibody possesses extensive immunological reactivity to venom components in snakes of distinct species and genera. The polyspecific immunological reactivity of the antibody showed a correlation with amino acid sequence identity and with predicted antigenic domains of JD9-analogues in venoms of snakes with closest phylogenetic links to B. jararaca. This study further promotes the potential of DNA immunisation to generate toxin-specific antibodies with polyspecific cover. An analysis of the reactivity of the JD9-specific antisera to B. atrox complex venoms that exhibited intraspecific variation in the venom proteome revealed, however, that the toxin-specific approach to antivenom development requires a more in-depth knowledge of the target molecules than is required for conventional antivenoms. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Bothrops jararaca; DNA immunisation; Toxin-specific antibodies; Immunological cross-reactivity 1. Introduction Viper venoms consist of numerous toxic components that cause haemorrhagic and coagulopathic, and occasion- ally neurotoxic, pathologies to the envenomed patient. Because of the inter- and intra-specific variation in the toxin composition of viper venoms, treatment of envenoming is best achieved by the administration of polyspecific anti- venom. Monospecific antivenoms are used preferentially if the envenomed patient identifies the snake responsible for the symptoms that are characteristic within a region (e.g. monospecific Echis viper antivenom in West Africa). Polyspecific antivenoms are prepared from the sera of horses or sheep immunised with increasing doses of whole venoms from the most medically important snake species within a defined region. Antivenoms therefore contain antibodies to the majority of venom components, irrespec- tive of their toxicity. While this comprehensive responsive- ness satisfies the polyspecific requirements of antivenoms, it also means that antivenoms contain numerous redundant antibodies specific to non-toxic venom antigens that dilute the efficacy of the toxin-specific antibodies (Theakston and Reid, 1983). This deficiency is exacerbated by the observation that the most toxic venom components are not necessarily the most antigenic, particularly those of low molecular weight (Mandelbaum and Assakura, 1998; Scho ¨ttler, 1951; Theakston, 1983). The development of toxin-specific antivenoms to address these issues was initially encouraged by the production of monoclonal antibodies with venom-neutralising potential (Boulain et al., 1982; Iddon et al., 1988; Perez et al., 1984; Pukrittayakamee et al., 1983). However, the prospect of monoclonal antivenoms never materialised because of the logistic problems of identifying and purifying, in sufficient 0041-0101/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. PII: S0041-0101(02)00360-4 Toxicon 41 (2003) 441–449 www.elsevier.com/locate/toxicon * Corresponding author. Tel.: þ44-151-705-3164; fax: þ 44-151- 705-3371. E-mail address: robharr@liverpool.ac.uk (R.A. Harrison).