In situ labelling of bone marrow lymphocytes with fluorescein isothiocyanate for lymphocyte migration studies in pigs.

In normal young pigs, the femoral artery and vein were cannulated and after occluding other vessels to one hind leg they were connected to an extracorporeal perfusion system. Fluorescein isothiocyanate (FITC) was added to the perfusate to selectively label cells in the bone marrow. Large numbers (approximately 0.9 X 10(9] of labelled lymphocytes left the bone marrow of one leg within 1 d and migrated via the blood to the bone marrow in other bones, lymph nodes, spleen, Peyer's patches and even into the thymus. On average 1.7% of the lymphocytes in the blood and about 1% within the spleen were labelled. Peyer's patches and the thymus showed very low indices. Thus the bone marrow is an integral part of the migratory route of lymphocytes. Selective labelling of bone marrow cells in their normal microenvironment with FITC is a suitable method for studies of cell migration from the bone marrow.