Ability of virus SV40 T-antigen to replace interleukin-2, a specific growth factor of T-lymphocytes

The entry of T-lymphocytes into the DNA-synthesizing phase is determined by three successive signals: an antigenic effect, interleukin-2 - a specific growth factor of T-lymphocytes - and by nonspecific serum growth factors, primarily transferrin. This system was used for a study of the effect of the T-antigen of virus SV 40 on the mitotic cycle. Purified T-antigen was injected alternately into T-lymphocytes using vesicles from erythrocyte ghosts instead of one of the control signals. It was established that the T-antigen cannot replace the antigenic effect, but is capable of replacing the specific growth factor interleukin-2. However, both normally proliferating T-lymphocytes and T-lymphocytes induced to divide have an absolute requirement for transferrin and probably for other nonspecific growth factors. It is suggested that the polymorphism of tumors caused by papovaviruses is determined by the ability of their early proteins to imitate the action on cells of growth factors specific for them.