Anaphylactic reaction to diphtheria-tetanus vaccine in a child: specific IgE/IgG determinations and cross-reactivity studies.

The present study describes the occurrence of an anaphylactic reaction after the administration of the fifth booster dose of DT vaccine in a six-year-old child. Skin test, in vitro determinations of specific IgE antibodies and immunoblotting assays showed that the IgE response was directed against tetanus and diphtheria toxoids (Dtx). IgG antibodies were also detected by ELISA and immunoblotting. The RAST and immunoblotting inhibitions showed no cross-reactivity between the two toxoids, indicating the presence of co-existing but non-cross-reacting IgE and IgG antibodies. This was maintained in two subsequent determinations done 18 and 30 months after the episode. To our knowledge, this is the first study of cross-reactivity between tetanus and diphtheria antigens. We show that simultaneous IgE antibodies to two different toxoids may occur, indicating that after an immediate reaction to DT, a search for IgE antibodies to both tetanus and Dtx should be undertaken.