Allogeneic tolerance in embryo aggregation mouse chimeras studied by mixed lymphocyte culture and cell-mediated lympholysis.

Tolerance in embryo aggregation (EA) mouse chimeras was investigated using mixed lymphocyte culture (MLC) reaction and cell-mediated lympholysis (CML). In most cases, spleen or lymph node cells from EA chimeras were specifically unresponsive toward their parental cells in both MLC and CML. There was no evidence to support the involvement of "serum-blocking factors" or suppressor cells under these experimental conditions. There was, however, an exceptional chimera in which cytotoxic T cell percursors reactive against one parental cell may have been present. We argue for classical clonal elimination being the primary mechanism for tolerance in EA chimeras and discuss a role of suppressor mechanisms for self-tolerance.