T‐Cell Regulation of Immunoglobulin Synthesis and Proliferation in Pokeweed (Pa‐1)‐Stimulated Human Lymphocyte Cultures

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Abstract
In pokeweed (Pa-1)-stimulated human lymphocyte cultures, T cells are essential for the survival, proliferation, plasma-cell development, and high-rate Ig secretion of B cells. Their effects are T-cell-specific in the sense that B-Cell stimulation does not take place in the absence of T cells even when fibroblasts or monocytes are provided. The experimental system is the most effective model for activation of human B lymphocytes so far described. Plasmablast development requires approximately 7 days in culture. In T + B-cell cultures established at 1 × 106/ml (1 × 104/mm2) initial cell density, plasma cells can secrete, on the average, as much as 40–70 pg IgM or IgG per cell per day. When the initial T-cell density is increased well above 1.0 × 106/ml, a T-cell-mediated depression of Ig synthesis becomes predominant. Thus, in the pokeweed model T-cell effects represent a balance of helper and suppressor influences. The study also shows that B cells are heterogeneous. A non-adherent IgG-committed (smIg−?) tonsil B-cell population seems to be less susceptible to T suppressor effects than normal tonsil B cells. This subset proliferates particularly well and synthesizes large quantities of IgG in the presence of large initial proportions of T cells.