Cyclosporin A Inhibits Thymus-dependent but not Thymus-independent Immune Responses Induced by Dextran B512

We have compared previous studies of the immune response to dexlran (Dx) B512 in thymus‐deficient nu/nu and thymectomized, lethally irradiated, and bone marrow‐reconstituted mice with those obtained with cyclosporin A (CyA) as a T‐cell‐inhibiting drug. Our data show that only immune responses to TD forms of Dx B512 are susceptible to suppression by CyA, whereas anti‐alpha 1–6 and anti‐DNP antibodies induced by high molecular weight dextran and DNP‐native Dx, respectively, were not inhibited. Similar results were obtained when polyclonal responses were studied. The polyclonal response induced by another dcxtran preparation, the polyanion dextran sulphate (DxS), was inhibited by CyA to the same extent as polyclonal T‐cell activation by T‐cell mitogens.