Specific inactivation of sensitized lymphocytes in vitro using antigens labelled with astatine-211.

This is a study of the use of astatine-211 as an alternative to iodine isotopes in radioactive antigen suicide experiments. The theoretical advantages of At are that it is a high energy (5·87 MeV), short half-life (7·2 hr)α-emitter with a short path length of 60 μm. Its destructive effect, measured in terms of degree of ionization per micron is 300 times that of I and I. Streptokinase (SK), tuberculin (PPD) and phytohaemagglutinin (PHA) were labelled electrolytically with At (3–9% incorporation). These antigens were not destroyed by the labelling technique or by self-irradiation during radioactive decay. Autoradiography showed that only a small fraction of lymphocytes bound At-labelled SK and PPD whilst most lymphocytes bound At-labelled PHA. Lymphocytes exposed for 40 min to 0·35–1·40 μCi of labelled antigens lost 35–83% of their ability to transform upon subsequent exposure to the unlabelled antigens. The inhibition was specific in that responsiveness to unrelated antigens was retained. These results extend our previous findings with the use of At in antigen suicide experiments.