A Critical Consideration of the Rat Epididymis as an Immunologically Privileged Site

Abstract

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.

The Initial Segment of the Rat Epididymis Is Able to Uptake Immature Germ Cells Shed by Testicular Damage

“…Although halo and basal cells of the epididymis hold features of immune cells [Hoffer et al, 1973;Yeung et al, 1994], they experienced no morphological changes. Nevertheless, the lack of immune proliferating cells is in agreement with the concept of immune privilege credited to the epididymis, where inflammatory responses are normally suppressed [Hoffer and Hinton, 1984;Kazeem, 1988]. In this context, principal cells of the epithelium take a major role in detecting and engulfing immature or abnormal germ cells flowing in the lumen, avoiding an unnecessary inflammatory reaction.…”

A dense network of dendritic cells populates the murine epididymis

“…Similarly, eDCs could be actively involved in the maintenance of the complex epididymal epithelium. In contrast with immunologically privileged sites such as the anterior chamber of the eye (Streilein 1993, Stein-Streilein 2008) and the brain, which are partially isolated from the immune system by a deficient lymphatic drainage, the epididymis contains abundant lymphatic channels (Kazeem 1983, Kazeem 1988). Therefore, immunological information gathered by eDCs could be processed in local lymph nodes to generate regulatory T cells and T effector cells.…”

Immunophysiology and Pathology of Inflammation in the Testis and Epididymis

“…By contrast, immune privilege in the epididymis has received little attention, and the limited available evidence indicates that the epididymis does not provide the same level of protection afforded by the testis, if at all. Some data indicate that allografts can survive slightly extended periods within the rat epididymis, but this could simply be related to regional differences in lymphatic drainage between animals, rather than local immunoregulation (Kazeem, 1988). Given the large variability in the historical success rate of studies on testicular immune privilege, it might be wise to reserve final judgment until more comprehensive data are available.…”