Molecular and Quantitative Analysis of Helper T Cell-Replacing Factors on the Induction of Antigen-Sensitive B and T Lymphocytes

Abstract

Murine spleen cells activated by the T cell mitogen concanavalin A (Con A) secrete factors that exhibit biologic activity on both bone-marrow (B) and thymus-derived (T) lymphocytes. In the presence of heterologous erythrocyte antigens, these factors stimulate antibody synthesis in T cell-depleted spleen cultures. In the presence of Con A, these factors stimulate mitogenic responses in thymocyte cultures where the cell density is too low to support mitogenic responses to Con A alone. Both culture systems have been developed as quantitative assays for the activities of the Con A factors. Purification of the biologic activities by salt precipitation, gel filtration, ion-exchange chromatography, and isoelectric focusing (IEF) establish that the molecules responsible for effects on B and T lymphocytes in these assay systems are identical. The quantitative assays performed reveal that these factors are active in each culture system at concentrations below 10^-9 M. The IEF-purified factors also stimulate the specific generation of cytotoxic lymphocytes to allogeneic tumor cells in culture. These experiments reveal a requirement for helper T cells in the induction of antibody synthesis in B lymphocytes, mitogenic responses to Con A in T lymphocytes, and cytotoxic T cell precursors to effector cells. Each assay system may be a measure of the induction of antigen-sensitive lymphocytes, suggesting that B and T lymphocytes respond to similar, if not identical, helper T cell activity.