The morphologic responses of the lymphoid system to homografts. I. First and second set responses in normal rabbits.

By JANINE ANDRI -SCHWARTL I HE REJECTION of a skin homograft by the rabbit is accompanied by the proliferation of large, basophilic cells (hemocytoblasts) in its lymphoid system.1-2 These cells first appear in the lymph node contiguous to the homograft; later, they are found in regional and distant lymphatic structures, but they are always most prominent in the lymph node draining the homograft. The administration of purine antimetabolites (6-mercaptopurine or thioguanine) inhibits the proliferation of hemocytoblasts and retards rejection of the graft. Those animals that reject the graft during treatment with antimetabolites develop an extreme proliferation of hemocytoblasts. This paper deals with an electron microscopic study of this reaction. During the first set homograft response, large, round cells containing numerous cytoplasmic ribosomes and very little endoplasmic reticulum were observed. On the other hand, many of the cells of the second set response were typical plasma cells, rich in endoplasmic reticulum. This feature was not evident by light microscopy. When 6-mercaptopurine was administered with a first set homograft, the large, ribosome-containing cells were lacking. However, in the animal rejecting its homograft despite the administration of 6-mercaptopurine, numerous large, extremely primitive cells were seen.