Use of (75Se)L-Selenomethionine as a label for lymphoid cells

[75Se]L-selenomethionine can be employed as a label for following lymphocytes in vivo. Its properties are broadly similar to those of 51Cr with regard to uptake, release of the isotope on cell death and reutilization; thus relatively high levels of 75Se in lymphoid tissue indicate the presence of viable labelled cells. It differs from 51Cr in that active release of selenium occurs from the labelled cells when the ambient cell concentration is low. No significant reutilization of leaked label occurs. Leakage of 75Se label occurs in vivo; this differs in the spleen and lymph nodes. Evidence is presented to suggest that 75Se losses reflect the transit times of cells through lymphoid organs.