The canine lymphoid system: A study of the effect of surgical excision

A detailed study of the lymph node anatomy of the dog is presented, and a technique for surgical excision of the thymus, spleen, and all gross lymph nodes is described. The dissections were performed after intravenous administration of pontamine blue to living animals. Major excision of the lymphoid tissue of the dog led to a modest prolongation of skin allograft survival, but it did not lead to a further increase in the allograft prolongation achieved with 6‐mercaptopurine immunosuppression when these two measures were used simultaneously. Neither did lymphadenectomy alter the leucopenia or toxicity of 6‐mercaptopurine when node excision was performed immediately prior to initiation of drug therapy. The transient nature of both the lymphopenia produced and the alteration of allograft response after lymphadenectomy suggest that there is another major contributor to the circulating lymphocyte pool. It is suggested that this may well be the lymphoid tissue in the intestinal wall. The surgical preparation described is proposed as a model for the study of lymphoid tissue depletion and regeneration in the dog.