Antiviral activity in sera of patients with Crohn's disease.

Sera from patients with Crohn's disease were tested for antiviral activity using a microtiter assay with end points showing 50% reduction of cytopathic effects. Patients were significantly more likely to have serum antiviral activity equivalent to interferon levels of 20 or more units/ml than were control subjects. The mean antiviral activity in the patients' sera (34 +/- 20 (s.d.) units/ml) was significantly greater than that in the control subjects' sera (0.6 +/- 1.7 (s.d.) units/ml). Following acidification the mean antiviral activity of the patients' sera (28 +/- 17 (s.d.) units/ml) had not changed significantly while heat inactivation resulted in significant loss of activity (7.5 +/- 2.7 (s.d.) units/ml). These findings are suggestive of the presence of circulating leucocyte interferon in the sera of patients with Crohn's disease.