Neutralization of crotoxin and crude venom by rabbit antiserum to crotalus phospholipase A

Immunotherapeutic potential of Crotoxin: anti-inflammatory and immunosuppressive properties

For the past 80 years, Crotoxin has become one of the most investigated isolated toxins from snake venoms, partially due to its major role as the main toxic component in the venom of the South American rattlesnake Crotalus durissus terrificus. However, in the past decades, progressive studies have led researchers to shift their focus on Crotoxin, opening novel perspectives and applications as a therapeutic approach. Although this toxin acts on a wide variety of biological events, the modulation of immune responses is considered as one of its most relevant behaviors. Therefore, the present review describes the scientific investigations on the capacity of Crotoxin to modulate anti-inflammatory and immunosuppressive responses, and its application as a medicinal immunopharmacological approach. In addition, this review will also discuss its mechanisms, involving cellular and molecular pathways, capable of improving pathological alterations related to immune-associated disorders.

Apoptosis-inducing factor of a cytotoxic T cell line: involvement of a secretory phospholipase A2

Natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) kill target cells by the granule-exocytosis pathway and by the engagement of molecules belonging to the tumor necrosis factor family. The involvement of secretory phospholipase A(2) (sPLA(2)) in the cytotoxic process has been proposed in NK cells. However, its molecular identity and intracellular localization remain unknown, and its mechanism of action is poorly understood. Here, we have readdressed this issue by studying the cytotoxic activity of whole cell extracts of a CTL line. We observed that inactivation of the perforin-granzyme pathway at 37 degrees C in the presence of 1 mM Ca(2+) enhanced the ability of CTL extracts to induce apoptosis. This potentiation of cell death was Ca(2+)-dependent, thermo-resistant, and inhibited by 4-bromophenacyl bromide and scalaradial (two inhibitors of sPLA(2)). The involvement of an sPLA(2) was confirmed by blocking the pro-apoptotic activity of the Ca(2+)-treated cell extract with an anti-sPLA(2) polyclonal antibody. By cell fractionation assays, we showed that the pro-apoptotic sPLA(2) was localized in the cytoplasmic fraction but not in perforin-rich granules or plasma membrane fractions. Western blotting analysis revealed the presence of four distinct bands of 56, 29.5, 21, and 15 kDa. The highest molecular weight band was consistent with the expression of a group III sPLA2. Taken together, these data indicate that an apoptosis-inducing sPLA(2) is expressed in the cytosol of a CTL cell line and suggest that it plays an effector role in CTL-mediated cytotoxicity.

Neutralizing potency of horse antibothropic antivenom. Correlation between in vivo and in vitro methods

The correlation coefficients between in vivo neutralization of lethal toxicity (ED50), neutralization of the hemolytic activity (PLA2) and levels of antibodies measured by ELISA, was investigated to test the potency of horse anti-bothropic antivenom. Twenty six horses were hyperimmunized with Bothrops venoms (B. alternatus, B. jararaca, B. jararacussu, B. neuwiedii and B. moojeni). To set up an indirect ELISA, for neutralization of PLA2 activity and for determination of ED50 in Swiss mice, the whole Bothrops jararaca venom (reference venom for assessing the bothropic antivenom potency in Brazil) was used. The toxic fraction (purified from B. jararaca venom by Sephadex G-100 chromatography) was also used as antigen for ELISA. All antivenoms analyzed effectively neutralized the lethal activity in the range of 1.6 to 9.6 mg/ml of antivenom. The correlation coefficient between ED50 and ELISA antibody titers against the crude venom and toxic fraction was r = 0.65 (P < 0.001) and r = 0.85 (P < 0.0001), respectively. Correlation between ED50 and neutralization of PLA2 activity was r = 0.52 (P < 0.01), and the correlation between ELISA antibody titers and neutralization of PLA2 activity was r = 0.58 (P < 0.002). Thus, the ELISA which measures only the antibody against the major toxic fraction of the B. jararaca venom should be most suitable for use as an in vitro assay of bothropic antivenom potency.

A comparison of in vitro methods for assessing the potency of therapeutic antisera against the venom of the coral snake Micrurus nigrocinctus

Therapeutic antisera against Micrurus nigrocinctus venom were tested for protection against lethality, as well as for inhibition of the nicotinic acetylcholine receptor (AchR)-binding and neutralization of phospholipase A2 (PLA2) activities of the homologous venom. Protection against venom lethality did not correlate with inhibition of AchR-binding activity, whereas there was a significant correlation between antisera potency and inhibition of PLA2 activity (r = 0.82, n = 10, P < 0.02). Inhibition of PLA2 activity could be useful in assessing the protective efficacy of M. nigrocinctus antisera during antivenom production. Micrurus nigrocinctus nigrocinctus venom proteins were fractionated by cation-exchange chromatography on Mono S FPLC and fractions assayed for lethality, AchR-binding and PLA2 activities. Antisera were titrated by enzyme-linked immunoassay (ELISA) against a crude M. n. nigrocinctus venom, two FPLC lethal fractions containing AchR-binding activity, and two toxins purified from M. n. nigrocinctus venom. No correlation was found between protective efficacy and the ELISA titer against any of these antigens. Compared to other elapid venoms that contain few toxins as major components, M. n. nigrocinctus venom appears to be more complex and its lethal effect is likely to be due to the combined effect of several neurotoxins.

An indirect haemolytic assay for assessing antivenoms

Dilutions of antivenom, venom, human erythrocytes and a phosphatidylcholine suspension, were incubated for 30 min at 37 degrees C. After centrifugation, the liberated haemoglobin was measured spectrophotometrically. The assay was used to assess an ovine antivenom against the venom from the South American rattlesnake, Crotalus durissus terrificus, and an equine Wyeth antivenin (Crotalidae, polyvalent). The ovine antivenom was more than five times as effective as the equine product. It also neutralized venoms from the Western diamondback rattlesnake, Crotalus atrox, and the fer-de-lance, Bothrops atrox. However, antivenoms raised against venoms from other Crotalus and Bothrops species provided little protection against the haemolytic activity of C. d. terrificus venom.

Phospholipase A2 injection in mice induces immunity against the lethal effects of Crotalus durissus terrificus venom

Phospholipase A2, purified from crotoxin obtained from C. d. terrificus venom, alone or incorporated in Freund's complete adjuvant (FCA) or in Al(OH)3 was used as an antigen to immunize mice against the lethal effects of C. d. terrificus venom. The animals were intracutaneously (i.c.) or subcutaneously (s.c.) injected with 60 micrograms of phospholipase A2, divided into three equal doses and injected every 7 days. Samples of blood were collected just before each injection and the sera used to determine the antibodies against whole venom by the ELISA method. The animals were s.c. challenged with 8 LD50 or with 16 LD50 28 or 95 days after immunization. The animals that received two s.c. doses of antigen followed by a third i.c. dose were partially resistant to 8 LD50 (58% protection). This resistance increased when the first two injections consisted of phospholipase A2, the third of whole venom, all i.c., all in Al(OH)3 (67% of protection). The maximal protection (90%) was attained when the animals were i.c. injected with phospholipase A2 in Al(OH)3 in all three immunizing doses. Antibodies against whole venom were detected 15 days after immunization, reaching a plateau on the twenty-eighth day and remaining unchanged at least until the ninety-fifth day after immunization.

Cross-reactivity and neutralization by rabbit antisera raised against crotoxin, its subunits and two related toxins

Antisera were raised against intact crotoxin (Crotalus durissus terrificus), Mojave toxin (Crotalus scutulatus scutulatus) and concolor toxin (Crotalus viridis concolor), as well as the subunits of crotoxin. Double immunodiffusion and enzyme-linked immunosorbent assays (ELISA) demonstrated antigenic similarity between these three purified toxins and their subunits. Additionally, when crotoxin antisera were pre-incubated with each of the three toxins before injection, the lethal activity of all were neutralized equally well. Antiserum was considerably more effective in neutralizing crotoxin in vivo when the toxin was injected i.m. than when injected i.v. Antisera against both intact crotoxin and its basic subunit were an order of magnitude more effective than crotoxin acidic subunit antiserum in crotoxin neutralization. Purified phospholipase A2 from Crotalus adamanteus and Crotalus atrox showed weak cross-reactivity with antisera raised against intact crotoxin and its subunits in the ELISA. Our results suggest that crotalid neurotoxins can be detected and neutralized by polyclonal antibodies raised against any intact toxin or basic subunit in this group of homologous toxins.

Titration of antiserum to South American rattlesnake (Crotalus durissus terrificus) venom by measuring inhibition of phospholipase A2 activity

Horse antiserum to the venom of Crotalus durissus terrificus, A South American rattlesnake, inhibits the phospholipase activity of the crude venom. There is a close relationship between this inhibitory property and the neutralizing potency of the antiserum in vivo. This may provide the basis for a rigorous standardization of anticrotalid venom in vitro.