The fungal metabolite gliotoxin: immunosuppressive activity on CTL-mediated cytotoxicity.

Gliotoxin, a potential etiologic agent which is synthesized by Aspergillus fumigatus and other pathogenic fungi, exhibits a variety of immunosuppressive activities. We have found that gliotoxin markedly inhibits both perforin-dependent and Fas ligand-dependent cytotoxic T-lymphocyte (CTL)-mediated cytotoxicity. Gliotoxin blocked granule exocytosis and the production of inositol phosphates in response to anti-CD3 stimulation. Apparently, activation signals were not efficiently received by the gliotoxin-treated CTL clone, perhaps because gliotoxin profoundly disturbed CTL cell attachment to immobilized anti-CD3. Although the expression of surface molecules of the CTL clone such as CD3 was unaffected by gliotoxin, the effector/target conjugate formation was inhibited dose-dependently by gliotoxin treatment of the effector CTL clone. These results suggest that gliotoxin prevents CTL from interacting with target cells.