Requirement of a Nonproliferating Class of Cells for Generation of Immune Responses in Cell Culture 1

Abstract

Summary

Numbers of unimmunized CBA spleen cells, too small to give a PFC response in culture by themselves, can produce PFC if they are cultured in the presence of a large number of heavily irradiated cells. The survival after irradiation of the PFC response by normal spleen cells has a D ₀ of 95–105 rads. In contrast, inhibition of the capacity of heavily irradiated spleen cells to facilitate PFC production by normal cells requires doses greater than 2.5 krads. Attempts to demonstrate the provision of a conditioning factor by the heavily irradiated cells were not successful. However, mixtures of normal and heavily irradiated cells in limiting dilution did result in PFC production. These results are in keeping with the hypothesis that cell—-cell interaction between the two cell populations is required for generation of PFC responses in culture. Since it is known that in thymus-marrow synergism in intact animals proliferation of both the thymus- and marrow-derived cell populations is required for PFC production, it is suggested that in culture a third, nonproliferating class of cells is also required. This class of cells can be detected in the spleen and lymph nodes but not in the thymus or bone marrow.