Activation of autologous reactive helper T lymphocytes for differentiation of human B lymphocytes.

We present experimental evidence that autologous reactive T cells are triggered to proliferate by HLA-D or Ia-like antigens on pokeweed mitogen-pulsed non-T cells and that a subpopulation of these proliferating cells in turn helps PWM-primed B cells to differentiate into immunoglobulin-secreting cells. These helper T cells displayed a proliferation kinetics different from that of other autologous reactive T cells in peaking on the second day of culture and were relatively resistant to irradiation or treatment with mitomycin C. Since heterologous anti-Ia antibody (F(ab')2 reagent) inhibits proliferation of helper T cells and the generation of plaque-forming cells, Ia antigen is an essential component in PWM-stimulated B cell differentiation. Anti-Ia reagent was shown to interfere with B cell differentiation in 2 ways. First, it abrogates the ability of PWM-primed non-T cells to activate helper T cells. Second, it directly affects a differentiation of B cells into Ig-secreting cells even in the presence of the activated helper T cells.