Regional lymphatics and lymph nodes of the testis, with reference to the testis as an immunologically privileged site

Immunologically privileged sites are those in which tissue allografts survive longer than in convectional sites. Privilege is usually attributed to absence or paucity of lymphatic drainage from these sites, preventing access of alloantigens to the regional node. There is evidence that the testis is a privileged site and this thesis examined certain aspects of its regional lymphatics and lymph nodes. 1. The existence of abundant lymphatics within the parenchyma of the testis was confirmed. 2. In guinea pigs and mice the extrinsic lymphatic trunks draining the testis were found to be uniform in pattern and to be interrupted, on each side, by at least one node, before entering the cisterna chyli. In rats, the pattern of extrinsic testicular lymph trunks was found to be variable. The left testicular trunk was always interuppted by at least one node. The right trunk, in 16 out of 52 rats, was not interuppted by any node but opened directly into the cisterna chyli. While such an arrangement might account for privilege of the right testis as a graft site in some rats, it clearly cannot be involved as an explanation in guinea pig and mouse. 3. In rats, the renal lymph nodes which receive lymph from the testis (and other sites) were found to belong to the category of haemolymph nodes. A detailed re-investigation of the structure of these nodes resolved several controversial issues:- a) haemolymph nodes possess both afferent and efferent lymphatics b) the erythrocytes, which are found in abundance within the nodes, either free in the sinuses or attached as rosettes around sinus macrophages, reach the node by afferent lymphatics and not by extravasation from intra nodal blood vessels. The kidney seemed to be the major source of erythrocytes, but other possible contributors were studied. 4. Lymph nodes regional to the testis show marked histological differences from nodes draining the pinna. They are "inactive" or "quiescent", with poorly developed cortical nodules, absent germinal cantres, inconspicuous thymus dependent cortex, narrow medullary cords and sparse plasma cells. The possibility was discussed that these appearances may be due in part at least to steroids which reach the nodes via the regional lymphatics of the testis and the adrenal gland and thus these steroids may influence the animal's response to an intratesticular allograft. 5, Six weeks after vasectomy the regional testicular lymph nodes of rats showed changes suggesting the genesis of humoral and cell mediated immunity. The nodes were enlarged, germinal centres were conspicuous, thymus dependent cortex was thickened and showed many immunoblasts and the medullary cords were enlarged and packed with plasma cells. Despite these changes, histological study of the testis and epididymus showed no sign of an autoimmune response