The lymphatic drainage of the rat prostate and its status as an immunologically privileged site

Recent suggestions that the rat prostate is an alymphatic, immunologically privileged site stimulated further investigation of its status using a variety of techniques. Fixation of certain organs by vascular perfusion of glutaraldehyde followed by plastic embedding avoids the distortion and stromal reorganization that often obscures evidence of lymphatic vessels in conventional histological preparations. When applied to the rat prostate, this technique revealed small lymphatic vessels at irregular intervals throughout the sparse stroma. Ink injected into the prostate drained from the organ into iliac lymph nodes within 3 to 4 hr. Enlargement of iliac lymph nodes within 1 week after injection of parental strain lymphoid cells into the prostate of F1 rats confirmed the drainage pattern. Ink and lymphoid cell injections into the bladder wall yielded comparable results, although ink reached iliac nodes sooner than it did in prostate injections. Immunological privilege was investigated by determining survival of skin allografts implanted in the prostate. Skin-into-prostate grafts bearing either major or minor histocompatibility antigens were rejected within a few days of similar orthotopic grafts. The inability of the rat prostate to allow significantly prolonged allograft survival as well as its demonstrated lymphatic drainage argues against an immunologically privileged status.