Continuous growth of mitogen-reactive B lymphocytes.

B-cell mitogens induce continous growth of murine lymphocytes in suspension cultures. Continuous growth is observed only at low cell densitiess, below 10(6) cells/ml, in regularly renewed medium containing beta-mercaptoethanol and a growth-supporting fetal calf serum. Continuous growth of B lymphocytes in culture appears to be favored by conditions under which maturation of Ig-secreting plaque-forming cells does not occur. On the other hand, maturation is observed whenever stimulated B cells cease to divide. This maturation leads to IgM secretion followed by secretion of IgG- or IgD-like molecules. Neither continuous growth of B cells nor the 'switch' to secretion of IgG- or IgD-like molecules requires the presence of T cells.