Relation between protective potency and specificity of antibodies in sera of tetanus immunized individuals.

Out of 157 human sera analyzed for antitetanus antibody content by ELISA, 13 turned out to contain only anti-BIIb antibodies, of which 8 proved to be neutralizing. Of these, the 3 sera 303, 306 and 312 together with a commercially available standard preparation of human antitetanus immunoglobulins were further analyzed as to their antibody composition by ELISA using plates sensitized with either the toxoid or various tetanus toxin-derived fragments. It was verified that the protective potency of these antisera was related mainly to their anti-BIIb antibody content. Adsorption experiments confirmed that anti-BIIb antibodies were primarily involved in toxin neutralization, although the presence of high levels of both anti-alpha and anti-Ibc antibodies could confer neutralizing capacity on the sera. A rabbit antiserum raised with the BIIb fragment resulted in a neutralizing antiserum that allowed us to calibrate the ELISA with the anti-BIIb antibodies as International Units.