Expression of tetanus toxin subfragments in vitro and characterization of epitopes

To define epitopes of tetanus toxin, we compared four different in vitro systems in terms of their ability to produce tetanus toxin-specific subfragments from cloned DNA. A transcription-translation system developed from a nontoxigenic strain of Clostridium tetani was found to yield predominantly full-sized peptides. Such peptides were used to map six different epitopes for eight monoclonal antibodies. The toxin-neutralizing properties of the antibodies were determined in an in vitro assay, based on the toxin-mediated inhibition of norepinephrine release from rat brain particles. Two monoclonal antibodies recognizing epitopes within the regions Ser-744 to Ser-864 and Ile-1224 to Asp-1315 could neutralize the toxin. A third nonneutralizing antibody was shown to recognize the synthetic peptide Phe-947 to Glu-967 derived from the tetanus toxin sequence. This peptide contains a human T-cell epitope.