In vitro immune response of human peripheral lymphocytes. I. The mechanism(s) involved in T cell helper functions in the pokeweed mitogen-induced differentiation and proliferation of B cells

Human peripheral lymphocytes (PBL) upon stimulation with PWM proliferate and differentiate to IgM- and IgG-producing cells. The PWM-induced Ig production in B cells was dependent on T cells, and cell-free supernatant (CFS) obtained from PWM-stimulated PBL or T cell-rich fraction replaced T cell helper functions. The active substance(s) in CFS were most likely derived from T cells. The kinetic studies showed that the proliferation of B cells took place in advance of the final differentiation to Ig-producing cells and that T cells or T cell product(s) had to exist at the initiation of cultures in order to give the maximum helper effect. However, the final differentiation of B cells to Ig-producing cells was not dependent on T cells. The helper effect of T cells or T cell product(s) on PWM-induced proliferation and differentiation of B cells was exerted across the MHC barrier. This may make it possible to apply this experimental system to the assessment of quantitative and/or qualitative changes in human helper T cells in several immunologic diseases.