Purification of murine helper T cell-replacing factors.

Humoral factors secreted by T lymphocytes and macrophages appear to play a role in cell communication leading to the triggering of immune responses. A factor has been purified from the culture supernatants of concanavalin A(Con A)-activated murine spleen cells with lymphokine activity in four assay systems. 1) stimulation of antibody responses to erythrocyte antigens in BALB/c.nu spleen cultures 2) amplification of production of cytotoxic T cells in thymocyte cultures, 3) stimulation of mitogenic responses to Con A in thymocyte cultures where the cell density is too low to support responses to Con A alone, and 4) maintenance of continuous T cell growth. The biologic activity has been sequentially purified by salt precipitation, gel filtration, chromatography, ion-exchange chromatography, and isoelectric focusing (IEF). These four lymphokine activities appear to be due to one class of molecules, termed Interleukin 2 (IL-2), with an apparent molecular weight of 30,000 daltons. A T cell lymphoma, LBRM-33 has been found to produce high titers of IL-2 activity upon mitogen stimulation. LBRM-derived IL-2 possesses similar chemical and biological properties to splenic-derived IL-2. The mode of action of IL-2 appears to be the clonal expansion of antigen- or mitogen-activated T cells. While mitogen-activated LBRM cells secrete IL-2, which appears to exert helper T cell-replacing activity via the expansion of pre-T cells in nude spleens, mitogen-activated spleen cells appear to secrete both IL-2 and another class of T cell-replacing factor (TRF). These findings raise the question of whether there exist multiple classes of factors with TRF activity. The identification of these molecules may lead to an understanding of the mechanism that regulates the induction of antigen-sensitive cells.