Differential biodistribution of native and 2 kGy 60Co irradiated crotoxin in tissues of CBA/J mice.

Crotalus durissus envenomation is treated using antivenins produced in horses. During production, animals have problems, sometimes followed by death, due to the high toxicity of the main toxin, crotoxin. Several methods tested to detoxify this toxin often resulted in decreased immunogenicity. Gamma irradiation has proved to be a successful method for crotoxin detoxification without loss of immunogenicity. We have studied the biodistribution of 2 kGy 60Co irradiated crotoxin (iCTX) in mouse tissues. We used both 125I-labeled iCTX or its detection by a specific immunohistochemistry assay (IHA). Both approaches showed similar early excretion of toxins by the kidneys. Higher iCTX uptake was seen in spleen and liver, which are rich in immune responder cells. In contrast to previous reports concerning native crotoxin (nCTX), we failed to detect iCTX in the neuromuscular junction, but both toxins were found on the kidney tubular cell surface, with rapid excretion that was more intense for iCTX. Kupffer cells and splenocyte macrophages presented IHA staining, as shown by the increased uptake of 125I toxin by these organs. No staining was observed in the brain, lung or heart, which also showed very low 125I counts. Allied to reduced toxicity, irradiation induced early endocytosis of crotoxin by phagocytic cells, improving antigen processing.