Migration of yolk sac cells to thymus grafts: requirement of prior sojourn in bone marrow (or liver?).

The migration of CBA/HT6T6 haemopoietic cells (adult bone marrow, embryonic liver or yolk sac) to established thymus grafts, in CBA/H 60-day neonatally thymectomized hosts, shows that all three cell types can migrate and divide within the grafts, albeit yolk sac cells appear later after cell injection. This last observation suggested possible intermediate steps, i.e. a sojourn in bone marrow (or liver in the embryos). When the same experiments were performed in hosts that had been pre-treated with 100 muCi of 89Sr (a bone seeking isotope), it was observed that marrow and embryonic liver cells still could migrate to thymus and subsequently generate a population of competent T lymphocytes, while yolk sac cells were incapable of such migration.