A NOVEL METHOD FOR LABELING HUMAN IMMUNOGLOBULIN-G WITH TC-99(M) SUITABLE FOR INFLAMMATION SCINTIGRAPHY

An amount of 1.0 mg human immunoglobulin G (hIgG) treated with ascorbi c acid at a molar ratio of 1:5000 for 16 h at 4-7 degrees C was mixed with 250 mu g GHA and 5 mu g stannous chloride dihydrate in normal sal ine. Radiolabelling of hIgG (>98%) was achieved instantly when mixed w ith Tc-99(m)-pertechnetate. The preparation was sufficiently stable in serum at 37 degrees C. The competitive binding assay and gel electrop horesis of the native and reduced hIgG did not show any measurable los s in immunoreactivity and intactness due to its reduction. There was n o significant decrease in the radiolabel of labelled hIgG when incubat ed with diethylenetriaminepentaacetate (DTPA) (50-fold), in contrast w ith about 9% loss of the radiolabel by treating it with a similar conc entration of cysteine. Blood clearance of labelled hIgG in rabbits was biphasic with about 78 min and 8 h as T-1/2 of the fast and slow phas es. Biodistribution of the radiotracer in mice at 4 h showed its uptak e by liver (10.2%), kidneys (5.39%), intestines (7.33%) and muscles (3 .9%), which altered to 5.63, 3.20, 4.03 and 6.73%, respectively, at 24 h. The radiotracer was excreted through both renal and hepatobiliary routes. High accumulation of the radiolabelled hIgG in inflammatory le sions of the patients confirmed the clinical usefulness of the method developed.