Accelerated immunological maturation in the chick.

A re-investigation has been made of the earlier claim by Simonsen (1957) that grafted immunologically competent cells (ICC) may proliferate indefinitely as evidenced by unlimited transferability of the graft—host splenomegaly in chick embryos. The observation was repeated, but the original interpretation proved untenable. A method of chimaera analysis was developed, based on neutralization of ICC with specific serum antibodies. Cells and antisera were mixed immediately before i.v. injection into the embryo and the neutralization assessed quantitatively by the reduction of spleen enlargement obtained in comparison with cells plus normal serum. It was found that the 17-day embryo recipient of ICC from an adult bird undergoes an accelerated immunological maturation which in 7 days confers upon its blood and spleen cells a higher degree of immunological competence, per unit number of cells, than in relevant controls. The first host is thus enabled to cause a GVH-reaction in a new 17-day embryo which, in turn, matures precociously. Hence a cycle is created which permits a serial transfer of splenomegaly for as long as the new host is antigenic to the previous host. The phenomenon was not repeatable with hosts of constant genotype. Accelerated maturation is not a mere antigenic stimulation of the young animal. So far it has only been produced by live cells, and only in conditions where the host is antigenic to the graft.