Urinary Immunoglobulin Components in Normal, Tubular, and Glomerular Proteinuria: Quantities and Characteristics of Free Light Chains, IgG, IgA, and Fcγ Fragment.

The urinary excretion of free light immunoglobulin chains IgG, IgA, and Fcγ fragment material has been estimated in 12 healthy individuals and 7 subjects with tubular or glomerular proteinuria. Measurements were carried out by immunochemical methods after separation of concentrated urinary immunoglobulin components by gel chromatography. Various components were isolated and their sedimentation constants, Stokes' radii, diffusion coefficients, molecular weights, and frictional ratios were determined.-Twenty-four hour urine volumes from the healthy subjects contained, on average, 3.3 mg of free light chains, 3.0 mg of IgG, approximately 2.0 mg of IgA, and 0.19 mg of Fey fragment Material. Normal urinary IgA included about 90% 11.5 S IgA of molecular weight 370000 and about 10% 7.0 S of molecular Weight 165000.-Patients with tubular proteinuria excreted relatively more of immunoglobulin components of small size than the patients with glomerular proteinuria. In particular, urine from patients with tubular proteinuria contained more free light chains than IgG whereas urine from patients with glomerular proteinuria contained more IgG than free light chains. The excretion of free light chains in the patients with tubular proteinuria was 8 to 33 times the average normal value. The results indicate an excess normal production of light chains assuming that all or most of the free chains originate from de novo synthesis. The relative amounts of urinary 11.5 S and 7.0 S IgA were similar in tubular proteinuria and normal proteinuria, whereas relatively more urinary 7.0 S IgA was found in glomerular proteinuria. This observation and the properties of the two IgA species suggest that the 11.5 S IgA is secretory IgA from the urinary tract and that most or all of the 7.0 S IgA originates from plasma.