Measurement of lymphocyte traffic with indium-111

This study was designed to assess the use of 111indium as a radioactive marker for the investigation of lymphocyte recirculation in the sheep. Lymphocytes were collected from sheep with indwelling catheters in the efferent lymphatic ducts of peripheral lymph nodes and labelled with 111In-oxine or Na2 51CrO at doses of 10 microCi and 50 microCi/10(8) cells respectively. After intravenous injection the lymphocyte specific activity (c.p.m./10(7) cells) in blood and lymph was measured for several days. The maximum specific activity in efferent lymph was twelve-fold greater with 111In than with 51Cr-labelled cells. The kinetics of lymphocyte traffic as measured in double labelling experiments was very similar. The modal transit time was 21.6 hr with each isotope. The recovery of 111In-labelled cells was not significantly different from cells labelled with 51Cr. In vivo viability of the labelled cells was further supported by the normal proliferative response observed with 111In-labelled lymphocytes compared to unlabelled cells in the normal lymphocyte transfer reaction. In conclusion, 111In-oxine is an excellent radioactive label for lymphocytes in the sheep. Because of its high counting efficiency and cell labelling characteristics one can label as few as 10 million lymphocytes, or a subpopulation of cells, and assess their recirculation.