Comparison of the immunogenicity and antigenic composition of several venoms of snakes in the family Crotalidae.

Crude venoms from the prairie rattlesnake (Crotalus viridis viridis), the western diamondback rattlesnake (Crotalus atrox), the eastern diamondback rattlesnake (Crotalus adamanteus) and the timber rattlesnake (Crotalus horridus horridus) were used to prepare monovalent antivenoms in rabbits. Each of these four monovalent antivenoms was reacted against six different venoms using the technique of immunoblotting (Western blot) to determine the relative immunogenicity of the four venoms and to compare the antigenic composition of six venoms. In addition to the four venoms listed above, venoms from the South American rattlesnake (Crotalus durissus terrificus) and the fer-de-lance (Bothrops atrox) were tested. SDS-PAGE showed that C. v. viridis venom contains the greatest number of components with 20, and the greatest number (7) less than 15,000 in mol. wt. C. durissus terrificus venom contains the least number of components, having 11. Immunoblotting experiments showed that the greatest reaction between venom and antivenom is not always obtained with the homologous system although the two greatest reactions obtained in this study were for two homologous reactions: that between monovalent anti-C. v. viridis venom and C. v. viridis venom, and that between monovalent anti-C. atrox venom and C. atrox venom. For antivenoms made to C. h. horridus and C. adamanteus venoms, the greatest reaction was obtained with C. atrox venom. There appeared to be no difference in immunogenicity between high-medium mol. wt (greater than 15,000) components and low mol. wt (less than 15,000) components in all systems tested except for C. atrox venom where two low mol. wt components gave a stronger reaction with the antivenom than would have been predicted based on their relative content in the venom as indicated by SDS-PAGE. If the immunoblots are scanned with a densitometer, both the qualitative (number of bands) and the quantitative (density of bands) reactions between venom and antivenoms can be taken into consideration by using a Reactivity Index (number of bands x density of bands). By comparing Reactivity Indexes of the various reactions obtained, the most cross-reactive antivenom tested was the monovalent antivenom to C. v. viridis venom, followed by anti-C. adamanteus, anti-C. atrox and anti-C. h. horridus in order of decreasing reactivity. The Reactivity Index can also be used to estimate the reactivity of a single antivenom with different venoms. The major limitation of this approach is the difficulty in standardizing the detection procedure using silver enhanced Protein A gold.