Quantitation of tetanus and diphtheria antitoxins in mouse sera by indirect haemagglutination.

Serum samples obtained from 75 groups of mice immunized with various doses of adsorbed tetanus vaccine, adsorbed diphtheria-tetanus vaccine and adsorbed diphtheria-tetanus-pertussis vaccine were titrated for tetanus antitoxin content by an in-vitro indirect haemagglutination (IHA) and by toxin neutralization test (TN) in mice. From these serum samples of 49 groups of mice which were immunized with combined vaccine containing diphtheria toxoid were titrated for their diphtheria antitoxin content by IHA and by i.d. toxin neutralization test (TN) in guinea pigs. Good correlations were found between the estimates obtained by in-vitro IHA and in vivo TN tests in both tetanus and diphtheria antitoxin titrations. The minimum level of tetanus or diphtheria antitoxin detectable by IHA was 0.00039 IU/ml. It is concluded that IHA is a simple, sensitive and reproducible alternative test which can replace the animal TN tests for the estimation of tetanus and diphtheria antitoxins and could reliably be used in the potency assay of tetanus and diphtheria toxoids of combined vaccines based on antibody induction in mice.