In vivo labelling of the spleen and mesenteric lymph nodes with fluorescein isothiocyanate for lymphocyte migration studies.

Lymphocytes in normal young pigs were labelled in vivo with fluorescein isothiocyanate in the spleen using an extracorporeal perfusion system and in mesenteric lymph nodes by direct injection into the nodes. Labelled lymphocytes leave the spleen at a high rate via the splenic vein and migrate to different lymphoid organs. Emigrants from mesenteric lymph nodes left the nodes more slowly and revealed a different homing pattern. Evidence is presented that a considerable number of lymphocytes from the parenchyma leave the nodes via the vein and not by the classical route of recirculating lymphocytes via the efferent lymphatics. Fluorescein labelling of lymphocytes in their normal micro-environment is a suitable method for lymphocyte migration studies.