A critical consideration of the rat epididymis as an immunologically privileged site.

A literature search reveals a lack of any previous attempt to implant foreign tissue into the epididymis. Instead, related studies have been carried out within the adjacent testis. Theoretically, there are peculiar immunobiological factors that can require separate consideration of the two adjacent sites. With this background, we designed the present work by removing the adjacent testis and subsequently used biochemical, histological, and electron microscopic methods to assess the fate of parathyroid allografts buried within the epididymis. Since the concept of immunological privilege is usually explained on the basis of the nature of lymphatic drainage, we also studied the pattern of lymphatic drainage at each allograft bed. In the analysis of our results, the animals were grouped according to the nature of lymph pattern from each transplant bed. We observed that prolonged survival of the tissue allograft occurred only when the lymphatic trunk draining the graft bed bypassed all retroperitoneal nodes and opened directly into the blood stream via the cisterna chyli. This anomalous survival is favoured by pretransplant splenectomy. These results demonstrate that the rat epididymis can sometimes be immunologically privileged.