Quantitation of J chain in human biological fluids by a simple immunochemical procedure.

The molecular form and immunochemical properties of the J chain populations released on reduction and carboxymethylation of normal human plasma, milk, saliva and of plasma containing IgA or IgM M-components were investigated. A procedure was devised to release the entire J chain population from these various sources and to produce immunochemically identical J chain populations containing only J chain monomers. An identical standard J chain population was purified and quantitated by physiochemical means. A specific rabbit anti-J chain antiserum was raised against this pure J chain population. A simple and rapid immunochemical method for J chain quantitation in complex biological fluids as well as in solutions of pure polymeric immunoglobulins was constructed on these grounds. The J chain concentration was found to be (mean +/- S.D.) 1.74 +/- 0.65 micron in normal human plasma, 1.94 +/- 1.21 micron in human milk and 0.48 +/- 0.26 micron in human saliva. The J chain/IgA molar ratio was found to be (mean +/- S.D.) 0.45 +/- 0.07 in human milk and 0.52 +/- 0.09 in human saliva when the IgA concentration was expressed as monomeric units per volume unit. The range of the J chain/IgA molar ratios in plasma samples with highly concentrated IgA M-components was 0-0.64. The J chain/IgM molar ratio in plasma samples with highly concentrated IgM M-components was between 1 and 2 when the IgM concentration was expressed as pentameric units per volume unit.