Immunoenzymatic assay of anti-diphtheric toxin antibodies in human serum

Abstract

An enzyme-linked immunosorbent assay was developed for measuring immunoglobulin G anti-diphtheric toxin antibodies in human serum. The assay was done in plastic plates coated with purified diphtheric toxoid. Since a straight-line relationship was found between logs of extinction values and of antibody concentrations, with a very constant slope, serum titers could be expressed as log1o of the serum dilution corresponding to a definite optical density, such as 0.5. The assay furnished highly reproducible titers on a continuous range, with coefficients of variation less than 10%. Only one or two serum dilutions were usually sufficient for serum titration. To establish correspondence of the enzyme-linked immunosorbent assay titers with biologically determined antitoxin international units, a regression equation was fitted between the respective values for 112 serum samples titrated in both tests. The enzyme-linked immunosorbent assay titer of 2.38 corresponded to an antitoxin titer of 0.01 U, which is considered as the minimal protective level. Simple to perform, economical, and precise, the immunoenzymatic assay seems to be a very practical procedure for seroepidemiological purposes.

Immunogenicity and safety following primary and booster vaccination with a hexavalent diphtheria, tetanus, acellular pertussis, hepatitis B, inactivated poliovirus and Haemophilus influenzae type b vaccine: a randomized trial in the United States

“…Seroprotection for diphtheria and tetanus was defined as an antibody concentration ≥ 0.1 IU/mL. 34,35 The assay cutoffs for the redeveloped and revalidated ELISA were 0.057 IU/ mL for diphtheria and 0.043 IU/mL for tetanus.…”

Immunogenicity and safety of a second booster dose of an acellular pertussis vaccine combined with reduced antigen content diphtheria-tetanus toxoids 10 years after a first booster in adolescence: An open, phase III, non-randomized, multi-center study

“…Antibody concentrations ≥0.1 IU/ml for diphtheria and tetanus were considered to provide a conservative estimate of protection. 39 , 40 As no correlate of protection is defined for pertussis antigens, 41 , 42 the newly validated ELISA cut-offs of 2.693 IU/ml for PT, 2.046 IU/ml for FHA, and 2.187 IU/ml for PRN antibody concentrations were used to define seropositivity.…”

Hexavalent vaccines: increasing options for policy-makers and providers. A review of the data supporting interchangeability (substitution with vaccines containing fewer antigens) and mixed schedules from the same manufacturer

“…Enzyme-linked immunosorbent assay (ELISA) was used to measure antibodies against diphtheria, tetanus, pertussis, and Hib antigens. Seroprotection was defined as an antibody concentration equal to or above the assay cutoffs of 0.1 IU/ml for diphtheria and tetanus and 0.15 µg/ml for Hib (anti-PRP) [34][35][36]. Seropositivity for pertussis antigens was defined as antibody concentrations above the assay cutoff of 5 ELISA units per milliliter (EL.U/ml).…”