Identification and neutralization of biological activities in the venoms of Loxosceles spiders

The biological activities of the venom of three species of spiders of the genus Loxosceles were studied (L. gaucho, L. laeta and L. intermedia). The dermonecrotic and lethal activities are shared by all three Loxosceles venoms. Only low levels of proteolytic, myotoxic and phospholipase A2 activities were demonstrable even when a large amount of venom was used. No direct hemolytic activitiy was detected. L. intermedia venom was the most lethal (LD50 0.48 mg/kg), the L. laeta venom was the least lethal (LD50 1.45 mg/kg) whereas L. gaucho venom showed an intermediate value (LD50 0.74 mg/kg). The anti-Loxosceles serum used (anti-arachnidic serum) was able to neutralize the most important activities (i.e., dermonecrotic and lethal activities) of the three venoms. SDS-PAGE and immunoblotting using the anti-arachnidic serum showed that almost all venom antigens were recognized by this antiserum. The possible mechanisms of action of the Loxosceles venom are discussed.

Suppresion of the antivenom antibody response by serum therapy

1. The antivenom antibody response of mice injected with Bathrops jararaca venom and receiving specific serum therapy was studied under different experimental conditions. Balb/c mice (18-22g) injected with venom (1.75 mg/kg) presented the clinical symptoms observed in patients bitten by B. jararaca and a high and long-lasting antivenom antibody response. 2. Injection of 0.1 ml of horse antiserum to venom 15 min after venom administration abolished the symptoms induced by the venom and induced an almost completely suppressed production of mouse antivenom antibodies. The extent of suppression of the antivenom antibody response depended on the dose of horse antiserum administered and was greater the sooner the serum therapy was applied after envenomation. 3. Injection of antiserum into envenomed mice that received an unrelated antigen (KLH) did not suppress the antibody response to KLH antigen though it inhibited production of antivenom antibodies. 4. Envenomed mice receiving an equivalent dose of F(ab')2 fragments obtained by pepsin digestion of horse antiserum presented the same extent of suppression of the antivenom antibody response as mice injected with the non-treated antiserum. 5. Mice whose antibody response was suppressed, when rechallenged with venom, presented a primary antibody response. 6. These results suggest that suppression of the antivenom antibody response presented by envenomed patients submitted to serum therapy is due to the masking of the venom epitopes by horse antibodies as well as to the rapid elimination of the venom epitopes