Age-dependent allospecific change in susceptibility to local lymph node GVHR in rats

Inoculation of parental strain lymphocytes into the footpads of young F1 hybrid rats induces GVHR, which can be quantitated by estimation of the weight of the popliteal lymph node 7 days later. In a number of strain combinations adult and old F1 animals were also useful for the assay. In some, however, it was observed that F1 rats did not support GVHR to the same extent as young did, when one of the parental strains served as donor for the GVHR, but reacted normally if the other parental strain was used. This phenomenon was analysed in serum and cell transfer experiments as well as in vitro in MLC. It was possible to transfer suppression in vivo, whereas some degree of specific MLC inhibition was observed when serum from old F1 animals undergoing GVHR was assessed. The 'old' pattern of response could be reverted partially by splenectomy and completely by low dose irradiation of the recipient before GVHR.