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In the present study, we recognized progressively high immunological cross-reactivity between Pseudocerastes persicus fieldi (Pf) venom and six other medically important Egyptian snake venoms belonging to families Viperidae and Elapidae. Antibodies with a range of bonding strengths were shown to be involved in such cross-reactivity. Two strategies have been tried to access specificity; (i) using affinity purified species-specific anti-Pf antivenom antibodies, (ii) conducting the assay in the presence of ammonium thiocyanate (NH4SCN). The discrimination power of the prepared species-specific antivenom was demonstrated by its ability to detect Pf venom over a range of Pf concentrations (2.5 ng-2.5 µg) in a variety of body fluids. The assay could distinguish circulating Pf antigens from other viper antigens in the whole blood of experimentally envenomed mice. What seems promising in our work is the use of the chaotrope, NH4SCN, which renders the reaction medium more favorable for the specific homologous antigen-antibody interactions, primarily via preventing lower avid antibodies to share and, to a bit lesser extent, by decreasing non-specific absorbance signals frequently encountered with ELISA assays. The ELISA described herein may be useful for clinicians for identification of snake bites inflicted by Pf snake species. Balancing between specificity and sensitivity has to be considered for best results.

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RESUMEN

Pertussis specific antibodies were studied with respect to quality and quantity in a cohort of apparently healthy Egyptian children and adolescents, with their age range between 1 and 18 years, in an attempt to get a close and clear insight into the current humoral immunization status in this specified group and to try find a relation between the antibody levels and their avidities in eradication of this devastating infectious disease. Our results showed that avidity increase was most marked in young school children (6-8 years) where it seemed to reach a plateau in older children and adolescents. Antibody titer was highest in toddlers (1-2 years) and young school children (6-8 years) groups, most probably following vaccination and/or booster doses. Among children aged 1-5 years, 28% had highly avid and 50% had high titer antibodies, whereas in adolescents aged 13-18 years, 70% had highly avid antibodies and only 30% had high titer antibodies. The results clearly demonstrated that while levels of anti-Bordetella pertussis (B. pertussis) antibodies wane with growing age, the avidity seems to increase, to a plateau, irrespective of further antigen exposure in a pattern showing complete independence of avidity on concentration. The present study draws attention to the importance of avidity measurements, together with conventional ELISAs, for evaluating immunity against pertussis. Being based on a limited sample size, it could open doors for larger-scale surveys to be possible indicators for the need and timing of booster vaccination doses among Egyptians.

RESUMEN

In this report, we present a study on the antigenic cross-reactivity of various venoms from the most dangerous Egyptian snakes and scorpions belonging to families Elapidae, Viperidae and Buthidae. The study was carried out with special reference to bonding properties between venoms and antivenoms and their involvement in the formation of specific and/or cross-reactive interactions. The homologous polyclonal antivenoms showed high reactivity to the respective venoms and cross-reacted with varying degrees to other non-homologous venoms. Assorting the antivenoms according to their susceptibility to dissociation by different concentrations of NH4SCN revealed that most of the antibodies involved in homologous venom-antivenom interactions were highly avid; building up strong venom-antivenom bonding. Whereas cross-reactions due to heterologous interactions were mediated by less avid antibodies that ultimately led to the formation of venom-antivenom bonding of different power strengths depending on the antigenic similarity and hence on the phylogenetic relationship of the tested venom. A new parameter evaluating high and low avid interactions, designated as H/L value, for each antigen-antibody bonding was initiated and used as an indicator of bonding strength between different venom-antivenom partners. H/L values were many folds higher than 1 for homologous and closely related venoms, 1 or around 1 for cross-reactive venoms, whereas venoms from unrelated remote sources recorded H/L values far less than 1. Using well defined polyclonal antivenoms, H/L value was successfully used to assign eight unknown venoms to their animal families and the results were confirmed by species-specific ELISA and immunoblotting assays.

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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.

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