Determination of alpha1-proteinase inhibitor by a new enzyme linked immunosorbant assay in feces, serum and an enterocyte-like cell line.
Although alpha(1)-proteinase inhibitor (alpha(1)-PI), the main serine proteinase inhibitor in human plasma, is predominantly liver-derived, the proof of fecal alpha(1)-PI is a maker for intestinal protein loss. Furthermore, alpha(1)-PI is synthesized locally by human intestinal epithelial cell lines (e. g. Caco-2). Therefore, we investigated the diagnostic value of a new enzyme-linked immunosorbent assay (ELISA) to detect alpha(1)-PI in serum, feces, and Caco-2 supernatants in comparison with radial immunodiffusion (RID). alpha(1)-PI concentrations assessed by ELISA were on an average 30 % higher than those measured by RID. Only the ELISA system detected alpha(1)-PI in supernatants of Caco-2 cells. Our data imply first that this ELISA system is more sensitive to assess alpha(1)-PI than other methods, and second that it obviously determines locally synthesized alpha(1)-PI which can not be liver-derived. However, further examinations are necessary to distinguish between enterocyte-derived or systemic alpha(1)-PI and its diagnostic relevance in bowel disease.