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 Na₂⁵₁CrO at doses of 10 μCi and 50 μCi/10⁸ cells respectively. After intravenous injection the lymphocyte specific activity (c.p.m./10⁷ 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.