A restricted component of T cell help in pokeweed mitogen-stimulated humans peripheral blood cell cultures.

Limiting dilution analyses using human T and B cells from the peripheral blood of individuals recently (2 to 5 weeks) boosted with tetanus toxoid or a combination of diphtheria and tetanus toxoids were performed in order to investigate the specificity of T cell help during in vitro pokeweed mitogen (PWM) stimulation. Limiting numbers of irradiated T cells were added to an excess of B cells and their ability to help 1) IgG anti-tetanus toxoid antibody or 2) IgG anti-tetanus toxoid and IgG antidiphtheria toxoid antibody production were compared. The helper activity for anti-tetanus toxoid antibody production did not dilute out at the same point as help for total IgG production. Cultures were observed at limiting dilutions of added helper T cells that produced anti-tetanus toxoid IgG or anti-diphtheria toxoid IgG but not both even though a sufficient number of potential specific IgG-producing B cells were present. A distribution analysis of the IgG anti-tetanus and IgG anti-diphtheria helper T cells indicated that the two subpopulations did not segregate together. Thus in the presence of PWM, individual helper T cells appeared capable of supplying help for a restricted number of B cells.