[Comparative efficacy of homologous and heterologous biologicals against diphtheria].

This research investigates the effectiveness of homologous (from the same species) and heterologous (from a different species) antitoxins in combating diphtheria toxins. The study found that homologous antitoxins present a prolonged circulation of specific antitoxic antibodies compared to their heterologous counterparts.

Study Procedure

• The researchers derived homologous hyperimmune sera by immunizing rabbits and guinea-pigs with a diphtheria toxoid according to a specific schedule.
• The immune sera from rabbits contained 70 – 100 IU/mL of antitoxin antibodies, and the sera from guinea-pigs contained 60 – 80 IU/mL.
• A heterologous equine diphtheria antitoxin was used for comparison in this study.
• The level of antitoxin in the experimental animals was measured based on the quantified ability of the sera under study to neutralize the specific dermonecrotic effect of the diphtheria toxin.

Results

• The concentration of the antitoxin in the blood of guinea-pigs immunized two days prior with either the heterologous equine antitoxin or the homologous antitoxin ranged between 0.06 – 0.125 IU/mL.
• Guinea-pigs from both groups were fully protected when given 5.64 LD50 of the toxin.
• Between 50 – 75% of the animals which received the homologous antitoxin were protected from higher doses of toxin, while all animals that received the heterologous antitoxin died after administration of higher doses of the toxin.
• The maximum concentration of the homologous antitoxin in rabbits was observed on the first day after administration, remained stable up to days 5 – 7 post-injection, halved on the 12th day, remained stable till days 15 – 16 post-injection, and reduced by half again on the 30th day. Thereafter, it remained stable for an additional 5 – 10 days.

Conclusion

• The use of homologous antitoxin prolonged the circulation of specific antitoxic antibodies in the body by 3 – 4 times compared to the heterologous antitoxin.