Immunogenicity of purified Habu snake-venom toxoid in guinea pigs and monkeys with special reference to HR1 component.

Purity of the parent toxin influenced greatly the immunogenicity in guinea pigs of HR1 component of Habu-venom toxoid. The potency of HR1 toxoid in terms of the immunizing unit (ImU) appeared to be related to the antigen and aluminum contents. The immune response of the animals differed depending on the purity of the toxoid when the dose-response curve was examined over a wide range of the antigen dosage. Anti-HR1 titers of the guinea pigs immunized with crude toxoid (adsorbed) reached a plateau at about 10-20 U/ml ane further rise was not remarkable even when the amout of the antigen was increased several times, while 200 U/ml (maximum 400 U/ml or higher) of annti-HR1 was produced with a large amount of highly purified HR1 toxoid. Purified toxoid showed an excellent immunogenicity also in monkeys. The amounts of antigens necessary for the basic immunization to resist the challenge with a certainly lethal dose of crude venom were 18 and 0.5 mg as protein, for a crude and a highly purified toxoid, respectively. The total amount of aluminum was also reduced from 8.1 (crude toxoid) to 0.5 mg (purified toxoid). Multiple injections for the primary immunization enhanced early production of anti-HR1 in monkeys. However, at later stage of immunization, significant correlation was observed between the amount of HR1 toxoid (in ImU) for the primary immunization and the circulating anti-HR1 titer irrespective of the schedule of immunization. Anti-HR2 higher than 10 U/ml was produced consistently in monkeys with HR2 toxoid of 1.0 ImU for the basic immunization. However, excess HR2 toxoid of more than 10 ImU seemed rather unfavorable for anti-HR2 production.