75SeL-selenomethionine: a new isotopic marker for lymphocyte localisation studies.

L-selenomethionine (SeM), an analogue of methionine containing Se, is incorporated by mouse and rat lymphocytes in vitro: labelled with 75Se (75SeM) it emits gamma-rays distinguishable in energy from those of 125I and 51Cr. The usefulness of 75SeM for lymphocyte localisation studies was investigated. Both B and T cells incorporated 75SeM. Reutilization of the isotope in the mouse after injection of killed cells or allogeneic cells into immunized recipients was 1-2% of the injected dose. The immunocompetence of labelled mouse T and B cells was assessed in irradiated recipients, no effect of 75SeM incorporation being found. The distribution of labelled lymphocytes from various tissues in syngeneic recipients was found to be comparable to that previously obtained with 51Cr.