RESUMEN
The avidity to the corresponding antigens is often higher than to the cross-reactive antigens. This was demonstrated with the highly cross-reactive elapid Egyptian snake venoms Naja haje (Nh), Naja nigricollis (Nn) and Walterinnesia aegyptia (Wa), and used for the differentiation among the three species in a simple ELISA-based assay. A three-step immuno-affinity protocol was followed and the titer and avidity of the different antibody (Ab) preparations were assessed and evaluated. The advantages offered by the avidity power of the venom specific antibodies (VS-Abs) obtained after one step purification, outweigh the specificity of the species-specific antibodies (SS-Abs) obtained after further purification. The efficiency of the VS-Abs as special immunodiagnostics was validated using 16 venom samples collected from individual snakes of different size and age at different time intervals. The avidities of the VS-Abs to the homologous venoms were 2.53 ± 0.4, 2.66 ± 0.31 and 2.8 ± 0.06 for Nh, Nn and Wa venoms respectively; whereas the avidity of the same Abs to the heterologous venoms could hardly exceed 1. Venom concentrations in the range between 10-1250 ng/well were detected with almost the same efficiency, an extra advantage that could be added to the assay to assure equal sensitivity allover the mentioned venom concentration range.