J chain 'jā-.chān n a relatively short polypeptide chain with a molecular weight of about 35,000 daltons and a high number of cysteine residues that is found in antibodies of the IgM and IgA classes
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[for “joiningâ€] a 15-kilodalton polypeptide occurring in all immunoglobulin polymers, a single J chain occurring in each IgM pentamer and in each IgA dimer, trimer, or tetramer.Medical dictionary. 2011.