Appearance of a helper activity by mouse serum in cultured lymphoid cells.

Manipulations which inhibit the development of non-specific suppressor T cells did not inhibit the development of a helper activity in culture. These manipulations include culturing only those spleen cells nonadherent to Sephadex G-10, CY-treatment of spleen donor mice, or culturing spleen cells in the presence of MS instead of FCS. Further investigation of the helper cell developed in cultures supplemented with MS indicated that both in vivo and in vitro immunizations with SRBC induced the most effective helper activity, and SRBC-ghosts or even sonicated SRBC-ghosts were also effective for in vitro immunization. CM containing IL 2 inhibited the development of a helper activity when added on Day 0 but not on Day 4. rIL 2, however, slightly augmented the development of a helper activity even when added on Day 0. The kinetics of anti-SRBC PFC response was not changed in the presence of the helper cell and augmentation of the response by the helper cell was seen on all the days tested. Augmentation occurred without further SRBC addition to anti-SRBC PFC generation cultures whereas it did not occur without "intact" responder spleen cells. The helper cell was resistant to X-irradiation and to the treatment with anti-Thy 1.2 plus C' but sensitive to the treatment with anti-Lyt 1.2 plus C'. The activity of nonspecific suppressor T cells dominated over that of the helper cell and the helper activity appeared only when the ratio of suppressor cells to helper cells was reduced to less than 1:4.