Single murine B cells can be induced to grow clonally by a combination of mitogens (dextran sulfate and LPS) and the presence of appropriate accessory cells. We show here that irradiated cells of a tissue culture cell line (WEHI-3) can substitute for naturally occurring adherent cells. Single-cell growth as well as Ig secretion are induced by irradiated cells of WEHI-3. There are no histocompatibility restrictions between the cells of the accessory cell line and the responding B cells. Under limiting dilution conditions, dextran sulfate and LPS act synergistically in inducing both growth and Ig secretion in these WEHI-3-dependent cultures. Although Ig synthesis occurs only in cultures where B-cell growth occurs, not all clones of B cells produce Ig. This is apparently not related to the clone size or to the number of initiated precursor cells; instead mitogen-induced growing B-cell clones seem to be heterogeneous with respect to Ig production.
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