Radioimmunoassays for type III procollagen amino-terminal peptides in humans.

Use of radioimmunoassay for the amino-terminal propeptide of type III procollagen for monitoring fibrotic processes in humans has been frustrating because of the nonparallel relation between results for the standard bovine antigen and human serum samples. In the radioimmunoassays I developed for this propeptide and its monomeric Col 1 domain, based on use of antigens from humans, serum samples generated less-steep inhibition curves than did the standard antigen in the propeptide assay; in the Col 1 assay, however, serum and urine samples both generated inhibition curves having the same slope as that generated with the standard Col 1 peptide. Concentrations of human fragment Col 1 in serum samples as measured with the Col 1 assay were usually double those obtained with the human propeptide assay, which in turn were two- to threefold those obtained with the bovine antigen assay. In control subjects and alcoholic cirrhotics the concentrations of antigen in urine and the daily excretion rates as measured with the assay for human Col 1 exceeded those reported previously. The presence of different antigen forms was demonstrated with both assays by gel-filtration analysis of serum and urine samples. The assay for human Col 1 should be suitable for routine clinical chemical use.