51Cr Labelling of Normal Human T and B Lymphocytes for Kinetic Studies in Vivo: Fundamental Lymphocyte Kinetic Considerations

Lymphocyte traffic between blood and tissues was assessed by 51Cr labelling of lymphocytes and subsequent autologous reinfusion in 10 normal elderly persons. The technique for isolation and platelet depletion of lymphocyte suspensions is described. By the labelling procedure used about 70 μCi 51Cr may be incubated in about 100 million lymphocytes. This permits measurement of lymphocyte-bound radioactivity on the T and B fractions separately. The blood disappearance curves for labelled lymphocytes indicate the existence of exchangeable pools in the tissues of T as well as of B lymphocytes, that of the T lymphocytes being apparently larger. A characteristic finding in the blood disappearance curves for total lymphocytes is an increase in lymphocyte-bound radioactivity in the blood 4–6 h after reinfusion, designated reappearance. The disappearance curve of the B lymphocytes shows reappearance 4–10 h after reinfusion, whereas that of the T lymphocytes falls exponentially without any recordable reappearance. On the basis of the disappearance curves and a knowledge of the topographic distribution of T and B lymphocytes in the lymphoid tissues, a model of T and B lymphocyte traffic in the lymph nodes is discussed. This model operates with T and B lymphocyte passage by way of postcapillary venules and describes the migration in and around the germinal centres. The T lymphocytes in the periphery of the germinal centres are assumed to derive mainly from the afferent lymph, whereas the B lymphocytes in the centres are exchanged with lymphocytes in the blood in an exchangeable pool. The functional implications are discussed.