OH(CENTER-DOT) TREATMENT OF TETANUS TOXIN REDUCES ITS SUSCEPTIBILITY TO LIMITED PROTEOLYSIS WITH MORE EFFICIENT PRESENTATION TO SPECIFIC T-CELLS

At inflammatory sites, before their processing, antigens are exposed t o oxygen free radicals released by activated cells. The effect of hydr oxyl radicals (OH.) on the structure of a protein antigen, tetanus tox in (TT) was investigated, as well as the consequences on processing an d presentation. A chemical system composed of Fe-EDTA, ascorbate and H 2O2 was used to produce physiological amounts of OH. radicals. TT expo sed to OH. radicals presented a marked decrease of its intrinsic fluor escence with a concomitant increase of the content of bityrosine, but no fragmentation of the protein was detected by SDS-PAGE. Processing o f the modified TT was analysed, by incubating TT at acidic pH with fra ctions enriched in plasma membranes and lysosomes obtained from a lymp hoblastoid cell line (LCL). Proteolysis of OH.-treated TT was less imp ortant than proteolysis of native TT, especially upon prolonged incuba tions. Oxidized TT presented by LCL cells induced a greater proliferat ion of three different TT specific T cell clones, compared to native T T. When proteolytic digests of TT were presented by fixed LCL cells to a homologous T cell line, the proliferative response obtained in the presence of digests of OH.-treated TT was sustained, even in the case of prolonged proteolysis, whereas the response to digests of native TT fell rapidly. The relative resistance of OH.-treated TT to proteolysi s appears thus responsible for its greater presentation to specific T cells, probably by protecting epitopes.