Removal of IgG from normal plasma and plasma from untreated patients with active Crohn's disease - effect on levels of contact factors

Protein G columns were used to remove IgG from human plasma, and the effect on levels of factor XII, factor XI and prekallikrein was studied in functi onal tests. IgG was detected in PAGE immunoblot experiments with Fc-specifi c antibodies. Removal of the bulk of IgG in a procedure based on a low plas ma dilution (1 + 2.5) allowed the passage of an IgG fraction along with the contact factors. This fraction was found to be present in higher amounts i n plasma from patients with Crohn's disease (n = 5) than in control plasma (n = 12). In a previous study, PAGE immunoblot experiments showed that part of the prekallikrein was removed along with IgG when a higher plasma dilut ion (1 + 10.8) was used (Scand J Clin Lab Invest 1999; 59: 55-64). This obs ervation was supported by results in the present work based on parallel ass ays with the peptide substrates S-2302 and Bz-Pro-Phe-Arg-pNA, The prekalli krein fraction removed was present in a functional state differing from the main part of prekallikrein by yielding kallikrein with a significantly inc reased activity against the substrate S-2366. This prekallikrein fraction w as present in higher amounts in patient plasma than in control plasma. Pare of the corresponding amidase activity was blocked by lima bean trypsin inh ibitor, suggesting its presence in association with factor XI. The results also indicated that prekallikrein activator activity was connected with thi s fraction. With the high dilution procedure an extensive removal of IgG fr om the patient plasma was obtained compared to the control plasma.