Enhancement of the primary cytotoxic response to membrane by a lymphokine costimulator.

The primary and secondary cytotoxic T cell responses of C57Bl/6 (H-2b) mouse spleen cells to P-815 membrane fragments (H-2d) were examined. The primary response required the addition of a supernatant from mitogen-stimulated spleen cells, or costimulator, to the culture medium. Costimulator had little effect on the secondary response unless the spleen cells were first passed through a nylon wool column. Our data suggested that secondary cultures produced their own costimulator and that adherent cells were required for its production. The possibility that adherent cells are needed to activate helper cells is discussed.