Induction of differentiation in a B lymphoma X B lymphocyte hybrid line. II. Intraclonal heterogeneity in growth, secretion of IgM, and cytokine production in response to lipopolysaccharide.

Murine B lymphocyte clones have proven to be useful models to study aspects of B lymphocyte growth and development. It had been previously shown that induction of TH2.2 (B lymphoma X B lymphocyte) with LPS resulted in differentiation into IgM-secreting cells (a feature similar to other B cells lines such as BCL1), and secretion of granulocyte-macrophage-CSF. Many transformed and nontransformed lines (including TH2.2) have been shown to generate progeny heterogenous in size and secretion of product when exposed to mitogen. We extend this study to demonstrate heterogeneity in secretion of IgM, granulocyte-macrophage-CSF, IL-3, and IL-6 in LPS-induced TH2.2. Clones generated by limiting dilution were heterogenous with respect to size, type, and quantity of product secreted. Microscopic clones ranged from 10 to about 1000 cells in size and could not be grown further; the majority secreted one product (mainly IgM). These clones were very efficient secretors of IgM and probably consist mainly of terminal-secreting cells. Microscopic clones secreting cytokine were also efficient producers. Visible clones from LPS-induced cultures grew to the same size as uninduced clones and were often restricted in secretion of products. Although the majority secreted three of four products (52%), many secreted IgM only or IgM and one cytokine. Although there was a strong tendency for clones to secrete multiple products, almost every secretory phenotype could be found. Amounts of different products secreted were not correlated, suggesting an additional level of independent control of this variable. Restriction of secretion was not due to genetic variation because visible clones originally restricted in secretion almost always produced all products when expanded and retested. These findings indicate that cells of TH2.2 were heterogeneous with respect to growth and secretion in the presence of LPS and were individually programmed for differentiative responses. The programming of cells was not permanent, but subject to dynamic change.