A study of the mode of lymphocyte recirculation in the dog.

Current view of lymphocyte recirculation holds that lymphocytes enter the nodes by migrating across the wall of their postcapillary venules, not by way of their subcapsular sinus. Having explained elsewhere our reasons to question the validity of the concept, we undertood to reinvestigate the problem. Lymphocytes were collected from the thoracic duct of dogs and labelled with3 H-cytidine. Each suspension of labelled cells was transfused to the dog having provided it. Analysis of radioautographs revealed that a significant amount of the labelled cells, which had migrated in the nodes, were present in their subcapsular sinus and the peripheral layer of their cortex. Among the nodes, the mesenteric nodes showed the greatest concentration of labelled cells. In addition, a substantial percentage of the injected lymphocytes, mostly small ones, were found in the lamina propria of intestinal villi and crypts. The findings indicate that, at least in the dog, a large fraction of the lymphocytes recirculate by entering the nodes via the afferent lymph, mostly that of the mesenteric nodes.