Assembly and secretion of pentameric IgM in a fusion between a nonsecreting B cell lymphoma and an IgG-secreting plasmacytoma.

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Abstract
A new immunoglobulin [Ig] product was obtained by hybridization of mouse cell lines arrested at different stages in B [bone marrow-dervied] lymphocyte development. One line had characteristics of an undifferentiated B cell that synthesizes monomeric IgM as a membrane receptor but does not express J chain. The 2nd line was representative of a fully differentiated plasma cell synthesizing large amounts of IgG and J chain, but no IgM. Fusion of the 2 cell types yielded independent hybrid clones that secreted pentameric IgM, normally the 1st product of antigen-driven B cell differentiation. Analyses of hybrid cells indicated that the IgM was expressed as a result of complementation between synthetic capacities of the parental lines. The hybrid cells synthesized monomeric IgM and J chain and assembled these components into a pentameric molecule with the expected stoichiometry of 1 J chain per 5 monomeric units. Induction of B cell differentiatioin apparently includes a signal for de novo synthesis of the J chain. The complementation achieved by this hybridization provides a system for identifying other intracellular events in B cell differentiation to IgM secretion.