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THYMUS‐INFLUENCED IMMUNOLOGICAL MATURATION OF EMBRYONIC LIVER CELLS1,2

SUMMARY The role of the thymus in the immunological maturation of mouse embryonic liver cells was studied, with the ability of the liver cells to cause a graft‐versus‐host reaction as the assay. Parental embryonic liver cells were tested for their ability to induce a graft‐versus‐host reaction in 1‐day‐old normal or neonatally thymectomized F1 mice. Splenomegaly induction in this instance was demonstrable, although weak. The response in thymectomized hosts was as good as that in normal hosts. Parental embryonic liver cells were injected into normal or thymectomized semiallogeneic F1 irradiated animals whose spleens were subsequently removed and tested for their ability to initiate an in vitro graft‐versus‐host reaction in syngeneic (F1) test explants. Positive responses were induced by spleens from both normal and thymectomized hosts, but there was considerable delay with spleens from the latter group. Since the only allogeneic cells in this system were liver‐derived, it is concluded that immunological maturation of embryonic liver cells, at least in the splenic environment, is thymus‐influenced but not entirely thymus‐dependent.