MAPPING THE MAJOR HUMAN T-HELPER EPITOPES OF TETANUS TOXIN - THE EMERGING PICTURE

Progress on the mapping of Th epitopes of tetanus toxin (tt) has been slow due to reliance on studies of clones. In this paper, human Th cel l epitopes of tt were mapped using proliferation tests on PBMC in resp onse to synthetic peptides. PBMC from nine donors were tested over the entire set of tt homologous overlapping dodecapeptides. The 1304 pept ides were initially tested as 66 pools, each containing an average of 20 peptides. PBMC from individual donors responded to as few as 1 and as many as 17 of the 66 peptide pools. The sequences responsible for p roliferation were identified for the two most frequently recognized po ols, and for another two pools within a major immunodominant region. T hree new epitope sequences were mapped in detail and based on their re cognition by most individuals are likely to be promiscuous. A cocktail of peptides including the newly identified Th cell epitopes was able to induce proliferation in PBMC from 24 of 31 tetanus toxoid (TT)-resp onsive donors. This cocktail is a chemically defined reagent that can be used to quantitate in vitro Ag-specific Th cells in PBMC from most subjects, and may thus be useful for serial measurements of specific i mmunity such as in subjects undergoing immunotherapy or immunosuppress ive treatment.