Activation of Cytotoxic Spleen Cells by Poly A : U .

The activation requirements ofT lymphocytes, especially cytotoxic T lymphocytes, has been a matter of considerable controversy. Cytotoxic effector T cells have been shown to be specifically induced after in vivo or in vitro immunization and polyclonally induced by T-cell mitogens (1-3). T-cell cytotoxic capacity is found 5-7 days after alloimmunization or 24-48 h after mitogen activation. These results imply that some reprogramming of the cell is necessary before the expression of effector functions. Activation of cytotoxic T cells has been found to be enhanced by T-T cell collaboration (4-6), to be dependent of the presence of macrophages (7), and to require DNA synthesis and cell division (8-10). T lymphocytes can be stimulated by complexes of synthetic polyadenylic:polyuridylic acid (poly A:U) 1 causing enhancement ofT-cell helper activity (11, 12). Poly A:U enhancement of helper functions cannot be explained by a mitogenic effect of the polynucleotides on T lymphocytes and is probably due to a stimulated production of antigen-nonspecific Tcell factors (13, 14). Such factors also interfere with the induction of tolerance to a Tdependent antigen-soluble bovine gamma globulin (15, 16).