Activation of C57BL/6 spleen cells by the mitogenic principle derived from mycoplasma arthritidis

A T cell mitogen derived from the supernatant of cultured mycoplasma arthritidis (MAS) has been recently discovered. Here we show that among a variety of strains, mycoplasma arthritidis was the only one elaborating the mitogen. Pools of MAS obtained at different occasions were quite variable in their biologic activity. Thus, in an attempt to obtain a more uniform preparation, MAS was semi-purified by Sephadex G-150 columns. Biologic activity eluted in a single peak in the molecular weight range of 13,000 daltons. "Nonresponsive" C57BL/6 spleen cells could be reconstituted to respond to MAS by the addition of 2-mercaptoethanol (2-ME). This reconstitutive effect was seen even when 2-ME was added 12 h after MAS. In further experiments, the lymphocyte culture technique was modified. Adherent spleen cells (AC) were grown and repeatedly washed before the simultaneous addition of nylon-purified T cells and MAS. Also in this experimental set-up, 2-ME could be added after the T cells. Finally, AC were cultured in the presence of MAS and after 4 h washed repeatedly. Subsequently, T cells and 2-ME were added. Also under these conditions, C57BL/6 spleen cells were capable of responding to MAS. These data suggest that 2-ME does not act on AC but on T cells. However, nylon-purified T cells in the complete absence of AC did not respond to MAS even in the presence of 2-ME. Thus, in order for the response to MAS to occur in "nonresponsive" C57BL/6 spleen cells, both AC and 2-ME are required. So far, our experiments have failed to conclusively unravel the mode of action of 2-ME. Yet, experiments using monoclonal antibodies against I-E have suggested that the response of "non-reacting" C57BL/6 spleen cells to MAS in the presence of 2-ME is not restricted by the molecule on the cell surface coded for by the I-E region.