Solid phase radioimmunoassay for β2-microglobulin; a sensitive index for renal allograft evaluation

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β2-Microglobulin (β2M), a low molecular weight protein of unknown function, was first isolated from the urine of patients with renal tubular disorders.1 It has been shown to be identical to a polypeptide noncovalently bound to the larger HLA molecule on the cell surface of nucleated cells and to have a close structural homology with the CH3 region of the IgG heavy chain.2, 3 This protein has been shown to be present on platelets, mononuclear cells and polynuclear white blood cells, but not on mature erythrocytes.4 It has also been found in human serum, cerebrospinal fluid, saliva, and colostrum.5 In serum it is present as a free monomer, which is filtered freely through the glomerular membrane, almost completely reabsorbed in the proximal renal tubules, and catabolized so that only relatively small quantities are excreted in the urine.6, 7 Its diagnostic use in several types of renal disease has been reported.6–9

We report our experience with radioimmunoassay for β2M and its use in monitoring human renal allograft function. Because serum creatinine is commonly used for this purpose, we measured β2M and serum creatinine serially in eight renal allograft patients in an attempt to determine the relative sensitivity of these two tests of allograft function.

Materials and methods

Radioimmunoassay for β2M. The reagents for the assay were purchased from Pharmacia, Piscataway, New Jersey. The antibody was bound to Sephadex as the solid phase. In a typical radioimmunoassay protocol, 100 μl of each standard 3 to 96 μg/1 was added to the appropriately marked tubes. . . .



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