[Selective adsorption of immune lymphocytes, synthesizing DNA, on corresponding target cells]

Lymphocytes of inbred mice immunized with allogenic tumour cells were labelled in vitro or in vivo by 3H-thymidine, washed out and incubated with target cells in the presence of "cold" thymidine. A fraction of labelled small and medium lymphocytes was demonstrated by autoradiography to be absorbed rapidly and specifically onto the corresponding target cells. When the non-labelled immune lymphocytes were preincubated with target cells for 2 hours, and 3H-thymidine was added to the medium at various time periods, the percentage of labelled small and medium lymphocytes which adhered to the target cells appeared to be reduced in the course of the incubation, with the target reaching the initial value after an 8-hour contact. Small and medium immune lymphocytes which synthesize DNA are supposed to be the effector killer fraction which do not transform into blasts during the interaction with the target cells.