Neonatal thymic contrasuppressor activity on graft versus host reactions towards self histocompatibility antigens. Parental effects.

The ability of fetal and neonatal F1 thymocytes to regulate parental graft versus host (GvH) reactions against self histocompatibility antigens was investigated. The results obtained showed that: (1) fetal F1 thymocytes were able to suppress both maternal and paternal GvH reactivity; (2) at birth, thymocytes were still able to suppress maternal GvH reactivity while no suppression of paternal reactions was detected; the ability to suppress maternal GvH reactions could be detected until day 3; (3) the loss of suppressor activity correlated with the ability of thymocytes to contrasuppress parental GvH reactions. Thus, 24-h F1 thymocytes showed contrasuppressor activity on paternal GvH reactivity and 4-day thymocytes on maternal reactivity. Thymic cells with contrasuppressor activity were shown to be Lyt-1+, CD4+, CD8- and adherent to Vicia villosa. These results suggest the existence of parental effects influencing the duration of thymic suppression and the subsequent appearance of contrasuppressor activity on GvH reactions against self histocompatibility antigens, according to the maternal or paternal origin of self antigens towards which the reaction is directed.