Micrurus snake species: Venom immunogenicity, antiserum cross-reactivity and neutralization potential

Immunological Cross-Reactivity and Preclinical Assessment of a Colombian Anticoral Antivenom against the Venoms of Three Micrurus Species

Snakebite accident treatment requires the administration of antivenoms that provide efficacy and effectiveness against several snake venoms of the same genus or family. The low number of immunogenic components in venom mixtures that allow the production of antivenoms consequently gives them partial neutralization and a suboptimal pharmacological response. This study evaluates the immunorecognition and neutralizing efficacy of the polyvalent anticoral antivenom from the Instituto Nacional de Salud (INS) of Colombia against the heterologous endemic venoms of Micrurus medemi, and M. sangilensis, and M. helleri by assessing immunoreactivity through affinity chromatography, ELISA, Western blot, and neutralization capability. Immunorecognition towards the venoms of M. medemi and M. sangilensis showed values of 62% and 68% of the protein composition according to the immunoaffinity matrix, respectively. The analysis by Western blot depicted the highest recognition patterns for M. medemi, followed by M. sangilensis, and finally by M. helleri. These findings suggest that the venom compositions are closely related and exhibit similar recognition by the antivenom. According to enzyme immunoassays, M. helleri requires a higher amount of antivenom to achieve recognition than the others. Besides reinforcing the evaluation of INS antivenom capability, this work recommends the use of M. helleri in the production of Colombian antisera.

Immune response to neurotoxic South American snake venoms

South American rattlesnakes (Crotalus durissus spp) and coral snakes (Micrurus sp) venoms are characterized by inducing a limited inflammatory innate immune response, in contrast to Bothrops sp snake venoms which exert a prominent inflammatory activity. Some Crotalus durissus spp venoms, in addition, exert immunosuppressive activities that hamper the development of neutralizing antibodies in animals immunized for antivenom production. Micrurus sp venoms are rich in low molecular mass neurotoxins that elicit a limited immune response. These characteristics make it difficult to generate antivenoms of high neutralizing activity. Therefore, the study of the mechanisms operating behind this limited immune response to venoms is relevant from both fundamental and practical perspectives. This review summarizes key aspects of the immune response to these venoms and discusses some pending challenges to further understand these phenomena and to improve antivenom production.

Unveiling underestimated species diversity within the Central American Coralsnake, a medically important complex of venomous taxa

Coralsnakes of the genus Micrurus are a diverse group of venomous snakes ranging from the southern United States to southern South America. Much uncertainty remains over the genus diversity, and understanding Micrurus systematics is of medical importance. In particular, the widespread Micrurus nigrocinctus spans from Mexico throughout Central America and into Colombia, with a number of described subspecies. This study provides new insights into the phylogenetic relationships within M. nigrocinctus by examining sequence data from a broad sampling of specimens from Mexico, Guatemala, Honduras, Nicaragua, Costa Rica, and Panama. The recovered phylogenetic relationships suggest that M. nigrocinctus is a species complex originating in the Pliocene and composed of at least three distinct species-level lineages. In addition, recovery of highly divergent clades supports the elevation of some currently recognized subspecies to the full species rank while others may require synonymization.

Toxic and antigenic characterization of Peruvian Micrurus surinamensis coral snake venom

Micrurus surinamensis is a semi-aquatic coral snake found in primary forest region and can cause relevant human accidents. In this work we investigated the toxic and antigenic activities of the Peruvian Micrurus surinamensis venom (MsV). We found that MsV show hyaluronidase activity but lack LAAO and PLA₂ enzymatic activities. Interestingly, MsV induce edematogenic responses but cannot cause nociceptive effects. Furthermore, MsV can reduce in vitro cell viability in MGSO-3 cell line derived from human breast cancer tissue. To evaluate its antigenic potential, rabbits were immunized with MsV, which proved to be immunogenic. ELISA, immunobloting and in vivo neutralization assays demonstrated that the specific rabbit anti-MsV antivenom is more efficient than the therapeutic Brazilian antivenom in recognizing and neutralizing the lethal activity of MsV. MsV differs in protein profile and biological activities from M. frontalis venom (MfV), used as control, which impairs its recognition and neutralization by Brazilian therapeutic anti-elapidic antivenom. We performed a SPOT immunoassay for the identification of B-cell linear epitopes in the main toxins described for MsV targeted by the elicited neutralizing antibodies previously produced. A membrane containing 15-mer peptides representing the sequences of five 3TFxs and five PLA₂s was produced and probed with anti- MsV antibodies. Results revealed important regions in 3FTx toxins for venom neutralization. Identifying the main MsV components and its biological activities can be helpful in guiding the production of antivenoms and in the optimization of treatment for coral snake envenomation in Brazil.

Cardiac Effects of Micrurus corallinus and Micrurus dumerilii carinicauda (Elapidae) Venoms and Neutralization by Brazilian Coralsnake Antivenom and Varespladib

In this work, we examined the action of two South American coralsnake (Micrurus corallinus and Micrurus dumerilii carinicauda) venoms on rat heart function in the absence and presence of treatment with Brazilian coralsnake antivenom (CAV) and varespladib (VPL), a potent phospholipase A₂ inhibitor. Anesthetized male Wistar rats were injected with saline (control) or a single dose of venom (1.5 mg/kg, i.m.) and monitored for alterations in echocardiographic parameters, serum CK-MB levels and cardiac histomorphology, the latter using a combination of fractal dimension and histopathological methods. Neither of the venoms caused cardiac functional alterations 2 h after venom injection; however, M. corallinus venom caused tachycardia 2 h after venom injection, with CAV (given i.p. at an antivenom:venom ratio of 1:1.5, v/w), VPL (0.5 mg/kg, i.p.) and CAV + VPL preventing this increase. Both venoms increased the cardiac lesional score and serum CK-MB levels compared to saline-treated rats, but only the combination of CAV + VPL prevented these alterations, although VPL alone was able to attenuate the increase in CK-MB caused by M. corallinus venom. Micrurus corallinus venom increased the heart fractal dimension measurement, but none of the treatments prevented this alteration. In conclusion, M. corallinus and M. d. carinicauda venoms caused no major cardiac functional alterations at the dose tested, although M. corallinus venom caused transient tachycardia. Both venoms caused some cardiac morphological damage, as indicated by histomorphological analyses and the increase in circulating CK-MB levels. These alterations were consistently attenuated by a combination of CAV and VPL.

Monoclonal-Based Antivenomics Reveals Conserved Neutralizing Epitopes in Type I PLA2 Molecules from Coral Snakes

For over a century, polyclonal antibodies have been used to treat snakebite envenoming and are still considered by the WHO as the only scientifically validated treatment for snakebites. Nevertheless, moderate innovations have been introduced to this immunotherapy. New strategies and approaches to understanding how antibodies recognize and neutralize snake toxins represent a challenge for next-generation antivenoms. The neurotoxic activity of Micrurus venom is mainly due to two distinct protein families, three-finger toxins (3FTx) and phospholipases A₂ (PLA₂). Structural conservation among protein family members may represent an opportunity to generate neutralizing monoclonal antibodies (mAbs) against family-conserved epitopes. In this work, we sought to produce a set of monoclonal antibodies against the most toxic components of M. altirostris venom. To this end, the crude venom was fractionated, and its major toxic proteins were identified and used to generate a panel of five mAbs. The specificity of these mAbs was characterized by ELISA and antivenomics approaches. Two of the generated mAbs recognized PLA₂ epitopes. They inhibited PLA₂ catalytic activity and showed paraspecific neutralization against the myotoxicity from the lethal effect of Micrurus and Naja venoms' PLA_2s. Epitope conservation among venom PLA₂ molecules suggests the possibility of generating pan-PLA₂ neutralizing antibodies.

South American snake venoms with abundant neurotoxic components. Composition and toxicological properties. A literature review

In South America there are three snake genera with predominantly neurotoxic venoms: Crotalus, Micrurus and Hydrophis, which include nine species/subspecies, 97 species and a single marine species, respectively. Although accidents with neurotoxic venoms are less frequent than those with anticoagulant, cytotoxic or necrotic venoms (e.g. from Bothrops), they are of major public health importance. Venoms from genus Crotalus have been extensively studied, while data on the venoms from the other two genera are very limited, especially for Hydrophis. The venoms of North and South American Crotalus species show biochemical and physiopathological differences. The former species cause bothrops-like envenomation symptoms, while the latter mainly have neurotoxic and myotoxic effects, leading to respiratory paralysis and, occasionally, renal failure by myoglobinuria and death, often with no local lesions. Micrurus and Hydrophis also cause neurotoxic envenomations. Many studies have isolated, identified and characterized new enzymes and toxins, thus expanding the knowledge of snake venom composition. The present review summarizes the currently available information on neurotoxic venoms from South American snakes, with a focus on protein composition and toxicological properties. It also includes some comments concerning potential medical applications of elapid and crotalic toxins.

Cross-reactivity of some Micrurus venoms against experimental and therapeutic anti-Micrurus antivenoms

We developed experimental equine polyvalent and monovalent antivenoms against the venoms of Micrurus (M.) fulvius, M. nigrocinctus and M. surinamensis and studied their immunochemical reactivity on the venoms used as immunogens and on M. pyrrhocryptus, M altirostris and M. balyocoriphus venoms. Assessment of the neutralizing capacity of the polyvalent experimental antivenom was based on inhibition of lethality (preincubation and rescue assay experiments in mice) and indirect hemolytic and phospholipase activities. The immunochemical reactivity and neutralizing capacity were compared with those of two therapeutic antivenoms used for the treatment of coral snake envenomation in North America and in Argentina. In general, the experimental antivenom conferred a comparable level of neutralization against the venoms used as immunogens when compared to the therapeutic antivenoms and a certain level of cross-neutralization against the other venoms. The results suggest the need for additional venoms in the immunogenic mixture used, in order to obtain a broad spectrum anti-Micrurus antivenom with a good neutralizing potency. Paraspecific neutralization of South American coral snake venoms, although present at a higher level than the neutralization conferred by available nonspecific Micrurus therapeutic antivenoms, was rather low in relation to the specific neutralizing capacity.

Micrurus surinamensis Peruvian snake venom: Cytotoxic activity and purification of a C-type lectin protein (Ms-CTL) highly toxic to cardiomyoblast-derived H9c2 cells

Micrurus surinamensis (Cuvier, 1817), popularly known as aquatic coral snake, has a broad geographic distribution in the Rainforest of South America. The purpose of this study was to investigate the cytotoxic effect caused by M. surinamensis venom in H9c2 cardiomyoblast cells and to identify protein components involved in cardiotoxic processes. Venom cardiotoxic potential is evidenced by cell viability reduction in a concentration-dependent manner. We have purified one of venom components responsible for this effect after three chromatographic steps: a cytotoxic 23.461 kDa protein, as determined by mass spectrometry. A 19-residue sequence (DCPSGWSSYEGSCYNFFQR) of the purified protein was deduced by MS/MS and exhibited high homology with N-terminal region of C-type lectin from snake venoms. This protein was named Ms-CTL. Morphologically, H9c2 incubation with Ms-CTL led to a significant cellular retraction and formation of cellular aggregates, as observed by microscopy phase-contrast images. Our results indicate that M. surinamensis venom is highly toxic to H9c2 cardiomyoblast cell and less or not cytotoxic to other cell lines, such as HaCat, VERO and U373. Results presented herein will help understanding the mechanisms that underlie cellular damage and tissue destruction, being useful in the development of alternative therapies against these coral snake bites.

Immunological cross-recognition and neutralization studies of Micrurus mipartitus and Micrurus dumerilii venoms by two therapeutic equine antivenoms

New world Coral snakes comprise 82 species of medical importance distributed from southeastern United States to Argentina. In Colombia, Micrurus mipartitus and M. dumerilii are responsible for most coral snakebite accidents. Although infrequent, the severity of these envenomings, as well as the limited information available on the neutralizing coverage of commercially available antivenoms, underscores the need to perform studies to assess the cross-neutralizing ability of these life-saving immunobiologicals. In the present work, we evaluated the cross-recognition and neutralization ability of two equine therapeutic antivenoms: PROBIOL and SAC-ICP. PROBIOL antivenom showed cross-recognition towards both M. mipartitus and M. dumerilii venoms, with a significantly higher binding to the latter in both whole-venom ELISA and fractionated-venom immunoprofiling. In contrast, SAC-ICP antivenom cross-recognized M. dumerilii venom, but not that of M. mipartitus. Lethality of M. dumerilii venom was neutralized by both antivenoms, with a slightly higher potency for the SAC-ICP antivenom. However, the lethality of M. mipartitus venom was not neutralized by any of the two antivenoms. Results uncover the need to include M. mipartitus venom, or its most relevant toxins, in the production of coral snake antivenoms to be used in Colombia, to assure the neutralizing coverage for this species.

An interactive database for the investigation of high-density peptide microarray guided interaction patterns and antivenom cross-reactivity

Snakebite envenoming is a major neglected tropical disease that affects millions of people every year. The only effective treatment against snakebite envenoming consists of unspecified cocktails of polyclonal antibodies purified from the plasma of immunized production animals. Currently, little data exists on the molecular interactions between venom-toxin epitopes and antivenom-antibody paratopes. To address this issue, high-density peptide microarray (hdpm) technology has recently been adapted to the field of toxinology. However, analysis of such valuable datasets requires expert understanding and, thus, complicates its broad application within the field. In the present study, we developed a user-friendly, and high-throughput web application named "Snake Toxin and Antivenom Binding Profiles" (STAB Profiles), to allow straight-forward analysis of hdpm datasets. To test our tool and evaluate its performance with a large dataset, we conducted hdpm assays using all African snake toxin protein sequences available in the UniProt database at the time of study design, together with eight commercial antivenoms in clinical use in Africa, thus representing the largest venom-antivenom dataset to date. Furthermore, we introduced a novel method for evaluating raw signals from a peptide microarray experiment and a data normalization protocol enabling intra-microarray and even inter-microarray chip comparisons. Finally, these data, alongside all the data from previous similar studies by Engmark et al., were preprocessed according to our newly developed protocol and made publicly available for download through the STAB Profiles web application (http://tropicalpharmacology.com/tools/stab-profiles/). With these data and our tool, we were able to gain key insights into toxin-antivenom interactions and were able to differentiate the ability of different antivenoms to interact with certain toxins of interest. The data, as well as the web application, we present in this article should be of significant value to the venom-antivenom research community. Knowledge gained from our current and future analyses of this dataset carry the potential to guide the improvement and optimization of current antivenoms for maximum patient benefit, as well as aid the development of next-generation antivenoms.

Crotamine in Crotalus durissus: distribution according to subspecies and geographic origin, in captivity or nature

Background:

Crotalus durissus is considered one of the most important species of venomous snakes in Brazil, due to the high mortality of its snakebites. The venom of Crotalus durissus contains four main toxins: crotoxin, convulxin, gyroxin and crotamine. Venoms can vary in their crotamine content, being crotamine-negative or -positive. This heterogeneity is of great importance for producing antivenom, due to their different mechanisms of action. The possibility that antivenom produced by Butantan Institute might have a different immunorecognition capacity between crotamine-negative and crotamine-positive C. durissus venoms instigated us to investigate the differences between these two venom groups.

Methods:

The presence of crotamine was analyzed by SDS-PAGE, western blotting and ELISA, whereas comparison between the two types of venoms was carried out through HPLC, mass spectrometry analysis as well as assessment of antivenom lethality and efficacy.

Results:

The results showed a variation in the presence of crotamine among the subspecies and the geographic origin of snakes from nature, but not in captive snakes. Regarding differences between crotamine-positive and -negative venoms, some exclusive proteins are found in each pool and the crotamine-negative pool presented more phospholipase A₂ than crotamine-positive pool. This variation could affect the time to death, but the lethal and effective dose were not affected.

Conclusion:

These differences between venom pools indicate the importance of using both, crotamine-positive and crotamine-negative venoms, to produce the antivenom.

Comparación de la eficacia, la seguridad y la farmacocinética de los antivenenos antiofídicos: revisión de literatura

En Colombia se presentan anualmente alrededor de 5000 casos de mordedura de serpiente y su tratamiento se basa en la neutralización con inmunoglobulinas completas purificadas, sin embargo, globalmente se utilizan antivenenos faboterápicos. Objetivo: Dar a conocer diferencias entre las generaciones de antivenenos, la importancia del veneno en la producción de anticuerpos, comparar aspectos farmacocinéticos y los efectos adversos en pacientes. Materiales Métodos: Se realizó una búsqueda de literatura en bases de datos utilizando combinaciones de los descriptores y términos Mesh, en inglés y español. Se cotejaron parámetros farmacocinéticos en estudios preclínicos y los efectos adversos en estudios clínicos. Resultados: Se encontraron diferencias debidas al tamaño de la fracción de la inmunoglobulina que la compone, así entre más pequeña es ésta, se observa mayor distribución a los tejidos y una vida media más corta, comparada con las moléculas más pesadas. Se encontraron estudios con disminución de efectos adversos con antivenenos faboterápicos 

A Combined Strategy to Improve the Development of a Coral Antivenom Against Micrurus spp

Accidents involving Micrurus snakes are not the most common ones but are noteworthy due to their severity. Victims envenomed by Micrurus snakes are at high risk of death and therefore must be treated with coral antivenom. In Brazil, the immunization mixture used to fabricate coral antivenom contains Micrurus frontalis and Micrurus corallinus venoms, which are difficult to be obtained in adequate amounts. Different approaches to solve the venom limitation problem have been attempted, including the use of synthetic and recombinant antigens as substitutes. The present work proposes a combined immunization protocol, using priming doses of M. frontalis venom and booster doses of synthetic B-cell epitopes derived from M. corallinus toxins (four three-finger toxins-3FTX; and one phospholipase A₂-PLA₂) to obtain coral antivenom in a rabbit model. Immunized animals elicited a humoral response against both M. frontalis and M. corallinus venoms, as detected by sera reactivity in ELISA and Western Blot. Relevant cross-reactivity of the obtained sera with other Micrurus species (Micrurus altirostris, Micrurus lemniscatus, Micrurus spixii, Micrurus surinamensis) venoms was also observed. The elicited antibodies were able to neutralize PLA₂ activity of both M. frontalis and M. corallinus venoms. In vivo, immunized rabbit sera completely protected mice from a challenge with 1.5 median lethal dose (LD₅₀) of M. corallinus venom and 50% of mice challenged with 1.5 LD₅₀ of M. frontalis venom. These results show that this combined protocol may be a suitable alternative to reduce the amount of venom used in coral antivenom production in Brazil.

Neurotoxicity of Micrurus lemniscatus lemniscatus (South American coralsnake) venom in vertebrate neuromuscular preparations in vitro and neutralization by antivenom

We investigated the effect of South American coralsnake (Micrurus lemniscatus lemniscatus) venom on neurotransmission in vertebrate nerve-muscle preparations in vitro. The venom (0.1-30 µg/ml) showed calcium-dependent PLA₂ activity and caused irreversible neuromuscular blockade in chick biventer cervicis (BC) and mouse phrenic nerve-diaphragm (PND) preparations. In BC preparations, contractures to exogenous acetylcholine and carbachol (CCh), but not KCl, were abolished by venom concentrations ≥ 0.3 µg/ml; in PND preparations, the amplitude of the tetanic response was progressively attenuated, but with little tetanic fade. In low Ca²⁺ physiological solution, venom (10 µg/ml) caused neuromuscular blockade in PND preparations within ~ 10 min that was reversible by washing; the addition of Ca²⁺ immediately after the blockade temporarily restored the twitch responses, but did not prevent the progression to irreversible blockade. Venom (10 µg/ml) did not depolarize diaphragm muscle, prevent depolarization by CCh, or cause muscle contracture or histological damage. Venom (3 µg/ml) had a biphasic effect on the frequency of miniature end-plate potentials, but did not affect their amplitude; there was a progressive decrease in the amplitude of evoked end-plate potentials. The amplitude of compound action potentials in mouse sciatic nerve was unaffected by venom (10 µg/ml). Pre-incubation of venom with coralsnake antivenom (Instituto Butantan) at the recommended antivenom:venom ratio did not neutralize the neuromuscular blockade in PND preparations, but total neutralization was achieved with a tenfold greater volume of antivenom. The addition of antivenom after 50% and 80% blockade restored the twitch responses. These results show that M. lemniscatus lemniscatus venom causes potent, irreversible neuromuscular blockade, without myonecrosis. This blockade is apparently mediated by pre- and postsynaptic neurotoxins and can be reversed by coralsnake antivenom.

A polyvalent coral snake antivenom with broad neutralization capacity

Coral snakes of the genus Micrurus have a high diversity and wide distribution in the Americas. Despite envenomings by these animals being uncommon, accidents are often severe and may result in death. Producing an antivenom to treat these envenomings has been challenging since coral snakes are difficult to catch, produce small amounts of venom, and the antivenoms produced have shown limited cross neutralization. Here we present data of cross neutralization among monovalent antivenoms raised against M. dumerilii, M. isozonus, M. mipartitus and M. surinamensis and the development of a new polyvalent coral snake antivenom, resulting from the mix of monovalent antivenoms. Our results, show that this coral snake antivenom has high neutralizing potency and wide taxonomic coverage, constituting a possible alternative for a long sought Pan-American coral snake antivenom.

Cross-recognition of a pit viper (Crotalinae) polyspecific antivenom explored through high-density peptide microarray epitope mapping

Snakebite antivenom is a 120 years old invention based on polyclonal mixtures of antibodies purified from the blood of hyper-immunized animals. Knowledge on antibody recognition sites (epitopes) on snake venom proteins is limited, but may be used to provide molecular level explanations for antivenom cross-reactivity. In turn, this may help guide antivenom development by elucidating immunological biases in existing antivenoms. In this study, we have identified and characterized linear elements of B-cell epitopes from 870 pit viper venom protein sequences by employing a high-throughput methodology based on custom designed high-density peptide microarrays. By combining data on antibody-peptide interactions with multiple sequence alignments of homologous toxin sequences and protein modelling, we have determined linear elements of antibody binding sites for snake venom metalloproteases (SVMPs), phospholipases A₂s (PLA₂s), and snake venom serine proteases (SVSPs). The studied antivenom antibodies were found to recognize linear elements in each of the three enzymatic toxin families. In contrast to a similar study of elapid (non-enzymatic) neurotoxins, these enzymatic toxins were generally not recognized at the catalytic active site responsible for toxicity, but instead at other sites, of which some are known for allosteric inhibition or for interaction with the tissue target. Antibody recognition was found to be preserved for several minor variations in the protein sequences, although the antibody-toxin interactions could often be eliminated completely by substitution of a single residue. This finding is likely to have large implications for the cross-reactivity of the antivenom and indicate that multiple different antibodies are likely to be needed for targeting an entire group of toxins in these recognized sites.

Although snakebite antivenom is a 120-year-old invention, saving lives and limbs of thousands of snakebite victims every year, little is known about the mechanisms and molecular interactions of how antivenoms neutralize snake toxins. Antivenoms are produced by immunizing large animals with cocktails of snake venoms resulting in antibodies recognizing toxic as well as non-toxic venom proteins to variable degrees. As a result, high doses of antivenom are needed for treating a snakebite victim, causing more severe adverse reactions due to a high burden of heterologous antivenom proteins. For the first time, we have characterized the antibody recognition sites on hundreds of pit viper toxins using high-throughput peptide microarray technology and an antivenom specific for three pit vipers inflicting a high number of bites in Central America. Most pit viper toxins are enzymes known to have a catalytic site important for toxicity. However, our results suggest that the employed antivenom generally does not target such sites, but instead inhibits toxicity by binding to alternative sites, possibly causing conformational shifts in the toxin structures or interference with toxin-target recognition. The identification of these toxin-specific recognition sites may explain why the antivenom is effective against certain snakebites from pit vipers whose venoms are not part of the immunization mixture.

Synthetic peptide antigens derived from long-chain alpha-neurotoxins: Immunogenicity effect against elapid venoms

Three-finger toxins (3FTXs), especially α-neurotoxins, are the most poorly neutralized elapid snake toxins by current antivenoms. In this work, the conserved structural similarity and motif arrangements of long-chain α-neurotoxins led us to design peptides with consensus sequences. Eight long-chain α-neurotoxins (also known as Type II) were used to generate a consensus sequence from which two peptides were chemically synthesized, LCP1 and LCP2. Rabbit sera raised against them were able to generate partially-neutralizing antibodies, which delayed mice mortality in neutralization assays against Naja haje, Dendrospis polylepis and Ophiophagus hannah venoms.

Exploration of immunoglobulin transcriptomes from mice immunized with three-finger toxins and phospholipases A2 from the Central American coral snake, Micrurus nigrocinctus

Snakebite envenomings represent a neglected public health issue in many parts of the rural tropical world. Animal-derived antivenoms have existed for more than a hundred years and are effective in neutralizing snake venom toxins when timely administered. However, the low immunogenicity of many small but potent snake venom toxins represents a challenge for obtaining a balanced immune response against the medically relevant components of the venom. Here, we employ high-throughput sequencing of the immunoglobulin (Ig) transcriptome of mice immunized with a three-finger toxin and a phospholipase A₂ from the venom of the Central American coral snake, Micrurus nigrocinctus. Although exploratory in nature, our indicate results showed that only low frequencies of mRNA encoding IgG isotypes, the most relevant isotype for therapeutic purposes, were present in splenocytes of five mice immunized with 6 doses of the two types of toxins over 90 days. Furthermore, analysis of Ig heavy chain transcripts showed that no particular combination of variable (V) and joining (J) gene segments had been selected in the immunization process, as would be expected after a strong humoral immune response to a single antigen. Combined with the titration of toxin-specific antibodies in the sera of immunized mice, these data support the low immunogenicity of three-finger toxins and phospholipases A₂found in M. nigrocinctusvenoms, and highlight the need for future studies analyzing the complexity of antibody responses to toxins at the molecular level.

Heterologous expression, protein folding and antibody recognition of a neurotoxin from the Mexican coral snake Micrurus laticorallis

Background

The cysteine-rich neurotoxins from elapid venoms are primarily responsible for human and animal envenomation; however, their low concentration in the venom may hamper the production of efficient elapid antivenoms. Therefore, the aim of the present study was to produce fully active elapid neurotoxic immunogens for elapid antivenom production.

Method

Cysteine-rich neurotoxins showed recombinant expression in two strains of E. coli, and were purified using affinity chromatography and reverse-phase HPLC (rpHPLC).

Results

The cDNA of the four disulfide-bridged peptide neurotoxin Mlat1 was cloned into a modified expression vector, pQE30, which was transfected into two different E. coli strains. The recombinant toxin (HisrMlat1) was found only in inclusion bodies in M15 strain cells, and in both inclusion bodies and cytoplasm in Origami strain cells. The HisrMlat1 from inclusion bodies from M15 cells was solubilized using guanidine hydrochloride, and then purified by rpHPLC. It showed various contiguous fractions having the same molecular mass, indicating that HisrMlat1 was oxidized after cell extraction forming different misfolded disulfide bridge arrangements without biological activity. In vitro folding conditions of the misfolded HisrMlat1 generated a biologically active HisrMlat1. On the other hand, the HisrMlat1 from the cytoplasm from Origami cells was already soluble, and then purified by HPLC. It showed a single fraction with neurotoxic activity; so, no folding steps were needed. The in vitro folded HisrMlat1 from M15 cells and the cytoplasmic soluble HisrMlat1from Origami cells were indistinguishable in their structure and neurotoxicity. Rabbit polyclonal antibodies raised up against biologically active HisrMlat1 recognized the native Mlat1 (nMlat1) from the whole venom of M. laticorallis. In addition, HisrMlat1 was recognized by horse polyclonal antibodies obtained from the immunization of elapid species from sub-Saharan Africa.

Conclusion

HisrMlat1 shows increased biological activities compared to the native peptide, and may be used as an immunizing agent in combination with other toxic components such phospholipases type A2 for elapid antivenom production.