The liver as a privileged site for parathyroid alloimplanation in the rat.

It has been suggested that the liver suppresses the immune response to alloantigen. This hypothesis was tested utilizing parathyroid implantation into the liver and muscles of inbred rats. Recipients were parathyroidectomized and, after significant hypocalcemia, donor parathyroids from minor histoincompatible rats were implanted either in liver or in thigh hamstring. In one experimental group second-set grafting also was tested. Graft survivals were evaluated by (1) duration of functional response (DFR), the period of time during which the serum calcium level remained above the postparathyroidectomy baseline, (2) maximal response (MR), the proximity of the postimplantation calcium peak response to the normal preparathyroidectomy calcium level. Parathyroid implants survived significantly longer in the liver compared to the muscle, only when implanted across minor histocompatible barriers. It is suggested that the liver may contain an inhibitor, capable of suppressing the lymphocytes and thus suppressing immune response, which can be demonstrated when the histocompatibility barrier is weak.