Morphologic features of spleen allografts in rats. Graft rejection, acceptance, or lethal graft-versus-host disease in the same donor-recipient pairing.

The structural changes in serial biopsies of spleen allografts in inbred histoincompatible rats are described. Three experimental procedures in the same donor-recipient pairing (PVG to AGUS) were employed and resulted in spleen graft rejection (Group I, no pretreatment), spleen graft acceptance (Group II, hosts pretreated with donor cells), and lethal GVH disease (Group III, donors pretreated with host cells). Striking features in the three groups were the variation of involvement of the periarterial lymphatic sheaths (PALS) shortly after grafting, and a substantial increase in hemopoiesis, particularly erythropoiesis, in the red pulp. The very "quiet" cellular reaction in the PALS of the host spleens in Group II corresponded with permanent graft acceptance. In Group III the previously sensitized allografts behaved rather like Group I host spleens and, by causing fatal GVH disease, demonstrated their immunologic superiority.