Structural heterogeneity of faecal α1 antitrypsin shown by immunoblot analysis in patients with Crohn's disease

Abstract

Faecal α1 antitrypsin was determined in 34 patients with Crohn's disease and in 19 healthy subjects by immune nephelometry. A structural analysis of faecal α1 antitrypsin was carried out using immunoblot analysis under non-reducing conditions. Native serum α1 antitrypsin migrated with an apparent molecular weight of 45 kDa. Proteolytic α1 antitrypsin fragments (5-42 kDa) were specifically immunostained in 13/19 and 22/34 stool samples from control subjects and from patients with Crohn's disease respectively. There was a weak correlation (r=0-47; p<0-02) between the molecular weight of fragmented α1 antitrypsin and the faecal concentration in both groups, indicating that α1 antitrypsin inhibits its own proteolysis by intestinal proteases in a dose dependent way. The incidence of polymeric forms (>45 kDa) was similar in patients (10/34) and control subjects (5/19). In only one case in each group was the native serum form of α1 antitrypsin found in faeces. We conclude that faecal α1 antitrypsin differs structurally from the native serum form. Immunochemical measurements, therefore, reflect rather than represent faecal concentrations of α1 antitrypsin. The controversial results in published reports may be partly explained by these findings. The molecular heterogeneity of faecal α1 antitrypsin is not specifically associated with Crohn's disease.