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Synthesis but not secretion of J chain by variant mouse myeloma cells which lose alpha-chain-synthesizing ability.

We have devised a rapid method for obtaining large amounts of J chain from IgA in the ascitic fluid of mice bearing the MOPC 315 tumor. The J chain was released by reduction from the MOPC 315 IgA adsorbed onto a DNP-lysyl-Sepharose column, and was further purified by DEAE Sephadex chromatography. The mouse J chain was characterized as to its electrophoretic mobility, amino acid composition, apparent size, presence in different immunoglobulin classes, and reactivity with an antiserum containing anti-J chain activity. Variant cell lines have been selected from the IgA-producing mouse myeloma cell line MOPC 315. The variants did not synthesize detectable quantities of alpha heavy chains but continued to synthesize and secrete light chains. J chain was synthesized by both parent and variant cell lines but only secreted by the parent cells. It is postulated that J chain synthesis is not dependent on alpha heavy chain synthesis, but that secretion of J chain by MOPC 315 cells occurs only because of its attachment to the Ig1 molecule.