Fetal intestinal transplants in syngeneic rats: a developmental model of intestinal immunity.

We conducted a longitudinal study of the development of lymphoid tissue in fetal small intestine transplanted to a subcutaneous site in adult syngeneic Fischer strain rats. Fetal jejunoileal segments obtained between 18 and 21 days of gestation were transplanted to a dorsal subcutaneous site on syngeneic adult rats. Three weeks later, intestinal segments greater than 2.5 cm in length were found in 70% of recipients. Each week for 6 wk post-transplantation, a full-thickness biopsy was obtained for histologic and immunohistologic examination. At the time of transplantation, fetal rat intestine did not display Peyer's patches, intraepithelial lymphocytes, lymphoid follicles, or IgA-containing plasma cells. These lymphoid structures reached adult levels by 4 wk after transplantation, and the sequence of development of the lymphoid structures in the transplants appeared to match the postnatal development of normal small intestine. After immunizing the in situ intestine or the transplanted fetal intestine with cholera toxin, the number of cells producing specific antibodies to the immunogen increased significantly in intestinal transplants and in situ intestine. In contrast, few if any cells synthesizing antibodies to cholera toxin developed in the transplants after i.p. immunization. This study suggests that fetal intestinal transplants behave as part of the mucosal immune system. This model may provide useful approaches to studying the development of mucosal immunity.