The rejection of renal homografts has been studied in sheep by transplanting kidneys into the neck and preserving the renal lymphatic drainage intact. Chronic fistulae were established in the transplanted renal lymphatics and lymph collected throughout the life of the graft.

The changes that occurred in homografts during the process of rejection were reflected in changes in the lymph. Large numbers of basophilic, blast, lymphoid cells appeared in the lymph, and lymph production in the grafted kidney increased 20–50 fold. Over a period of about 10 days, up to 60 g wet weight of lymphoid cells and up to 10 liters of lymph were collected from the graft.

Within 24 hr of grafting, the host cells present in the renal lymph had become sensitized to the graft and transformed into blast cells when cultivated in Millipore chambers in vitro. When the cells leaving the graft during the first 18–48 hr were injected into distant nonstimulated lymph nodes of the host sheep, they evoked significant cellular and antibody responses in the nodes.

Within the graft, the main pathological changes were found in the vascular endothelium and many of the peritubular capillaries become plugged with emboli comprised of blast cells. There was extensive infiltration of the renal parenchyma with lymphoid cells and evidence of their transformation and proliferation within the renal blood capillaries.

When all the lymph and cells leaving the homograft were diverted from the body, there was a greatly decreased reaction in the regional prescapular lymph node, and no reaction in lymph nodes distant from the graft. In these circumstances, the survival of the graft was not prolonged, and it was rejected without involvement of the lymph nodes of the host.

Humoral antibody was produced in the lymph node regional to the homograft within 48–60 hr of grafting. Antibody was not detected in the blood or in the renal lymph until near to the time the graft was rejected. It was thought that this was due to the binding of antibody by the kidney graft tissue.

We conclude that all the events which lead to the recognition and rejection of renal homografts can occur centrally within the graft itself.

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