Fluorescein isothiocyanate as a cell marker for tracing lymphocyte circulation in sheep.

The use of fluorescein isothiocyanate (FITC) as a cell marker in ovine lymphocyte circulation studies was investigated. The effects of the label on lymphocyte function were assessed by lymphocyte blastogenesis, cell-mediated cytotoxicity and normal lymphocyte transfer reactions. Labelling lymphocytes in 0.05 mg FITC/ml for 10 min at 37 degrees C was found to be optimum. Circulation kinetics of FITC-labelled efferent lymph lymphocytes were monitored as they disappeared from peripheral blood following intravenous infusion and reappeared in the efferent lymphatic duct of the popliteal lymph node. No functional changes were detected in lymphocytes labelled with the optimal regimen.