Essential role of tumor necrosis factor-α in the differentiation of human tonsil in vivo induced B cells capable of spontaneous and high-rate immunoglobulin secretion

Human tonsils contain B cells capable of spontaneous and high-rate immunoglobulin (Ig) secretion in vitro. These cells are in vivo induced mature B cells, and, as such, they provide an adequate model for studying tonsil B cell differentiation. The present report analyzes the effect of a variety of factors on purified tonsil B cells capable of spontaneous IgG secretion in fetal calf serum (FCS)-containing and serum-free supplemented cultures. Tumor necrosis factor-(TNF)α was found to be important for these B cells to reach the high-rate IgG-secreting stage, as is indicated by the following findings: (a) none of the factors used modified tonsil B cell IgG secretion in FCS-containing cultures; (b) TNF-α (5-20 ng/ml), but not other cytokines or factors including interleukin (IL)-6, was capable of restoring missing IgG production in serum-free supplemented cultures of tonsil B cells; and (c) IgG secretion in FCS-containing cultures was inhibited by the addition of blocking anti-TNF-α antibodies, but not anti-IL-6 antibodies, and this inhibition could be specifically reversed by exogenous TNF-α. TNF-α was actively produced by tonsil B cells (range 120-750 pg/ml) in the presence, but not in the absence, of FCS. The TNF-α inductive effect occurred during the first 12 h of culture and did not require DNA synthesis. These results indicate that the early and endogenous generation of TNF-α seems to be essential for tonsil in vivo induced B cells to differentiate into the high-rate Ig-secreting stage.