Detection of Bence-Jones protein in serum by immunoblotting

To detect Bence-Jones protein (BJP) in serum we precipitated intact immunoglobulins (Ig) using polyethylene glycol (PEG) and subjected the BJP in solution to electrophoresis in agarose gel, followed by transfer to a polyvinylidene difluoride membrane, and immunoenzymatic staining (successively using rabbit anti-human light/heavy chain of Ig, biotinylated swine anti-rabbit Ig, and alkaline phosphatase-conjugated streptavidin). Treatment with PEG effectively reduced background staining of polyclonal Ig in the immunoblots, although intact monoclonal Ig was not always completely removed. To compare the present method with immunoelectrophoresis (IEP), we selected samples from patients demonstrating BJP by IEP in both serum and urine (n = 40), serum only (n = 18), and urine only (n = 32); 21 of these patients had BJP alone and 69 had BJP in addition to intact monoclonal Ig. Efficiency of detection of BJP in serum was increased by the present method: serum BJP was detected in 70 patients by the present method versus 58 by IEP. The present method demonstrated single BJP bands in the samples from 16 patients (kappa, n = 7; lambda, n = 9) and multiple BJP bands (range: 2-9) in the samples from 54 patients (kappa, n = 31; lambda, n = 23). This method could be useful for detecting BJP in serum from patients suspected of having light chain gammopathy (without the need for urine testing) and may complement urine testing in patients excreting polyclonal free light chains of Ig.