Suppression of the antivenom antibody response by serum therapy

1. The antivenom antibody response of mice injected with Bothrops jararaca venom and receiving specific serum therapy was studied under different experimental conditions. Balb/c mice (18-22 g) 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.