Activation of human peripheral blood lymphocytes by a trypanosome-derived mitogen.

Activation of human peripheral blood lymphocytes from unsensitized donors by fractions of T.b rhodesiense has been demonstrated in vitro. Both T and B cells were stimulated to differentiate into blast cells. Purified T cells failed to proliferate, but did so when mitomycin C-treated non-T cells were added. Non-T cell proliferation (weak in comparison to the T cell response) was shown to be T-dependent. In unseparated cell cultures. cultures, IgM synthesis was enhanced, whilst IgG synthesis was unaltered. However, reconstitution of non-T cells with equal number of irradiated T cells resulted in enhanced IgG synthesis. Thus neither T nor B cells were activated directly, but required the co-operation of accessory cells to proliferate. The role of monocytes in the regulation of this response requires further assessment.