Splenic suppressor cells in fetal and newborn mice.

Newborn mice are refractory to sensitization with picryl chloride and the graft versus host reaction (GvHR) in F1 fetal mice injected with parental lymphocytes is markedly reduced. Moreover, spleen cells (but not thymic lymphocytes) of fetal or newborn animals are able to suppress the cell-mediated immune responses, contact sensitivity (CS) and GvHR in a variety of experimental situations. The inhibitory cells are thy-positive and their suppressive activity wanes early after birth.