IMax Planck Institute for lmmunobiology, Freiburg, FRG 2University of Konstanz, Faculty of Biology, Konstanz, FRG

Addendum: Workshop 2

9a. Age Dependence of the Isogeneic Barrier in Nude Mice

H. MOLL1 and R. BOSING-SCHNF.rm:R2

Syngeneic memory cells can be stimulated to give a secondary immune response after transfer into irradiated euthymic recipients as well as into young thymuslcss nude mice. It is shown that nude mice more than twelve weeks of age arc not permissive towards memory cell activation as it is found in nonirradiated cuthymic animals . This barrier to isogeneic or congeneic cells seems to be caused by a pool of cyclophosphamide-sensitive cells (treatment with 20 rug/kg). Since young nude mice could be rendered as unpermissive as older nude mice by pretreatment with either PNA-agglutinable thymus cells or hydrocortisone-resistant thymocytes. it is suggested that an increased number of precursor T cells in older nude mice might exert this effect, atthough we did not succeed in concentrating or isolating suppressor cells from unpermissive recipients. It cannot be decided whether T cells can convey suppres­sion directly or whether they cause unpermissiveness indirectly through an idiotypic-anti­idiotypic regulation.