Abstract
Using monospecific antibody to human urinary trypsin inhibitor, we developed a highly specific and sensitive radioimmunoassay (RIA) for measuring human urinary trypsin inhibitor. No cross-reactivity of the antibody with protein standard serum, which contained albumin, α(1)-antitrypsin, haptoglobin, α(2)-macroglobulin, transferrin, IgG and IgA, was observed. The sensitivity of the system was 10 ng of trypsin inhibitor per assay tube, and 5-10 μl of urine was sufficient to determine the concentration of trypsin inhibitor in urine. The amounts excreted in the urine of 10 healthy men and 10 healthy women were 4.83 ± 2.46(mean ± SD) and 3.86 ± 1.35 mg/day, respectively. The correlation between estimates by RIA and those by enzymic assay was r = 0.96 (p < 0.005). The method proposed here can be used to determine the concentration of urinary trypsin inhibitor in a small amount of biological fluids and cells.