Free light chains of immunoglobulins in normal serum and urine determined by radioimmunoassay.

A radioimmunoassay for determination of free light polypeptide chains from human immunoglobulins in serum and urine is described. The free light chains were isolated from the regular immunoglobulins by gel filtration on Sephadex G-100 columns. In the radioimmunoassay the free and antibody-bound 125I-labelled light chains were separated on gel filtration through Sephadex G-200 columns. The mean concentration of free light chains in serum from 20 normal subjects was 10.6 mg/1 for lambda chains and 13.2 mg/1 for kappa chains. The 24-hr urinary excretion was 1.1 mg for lambda chains and 3.2 mg for kappa chains.