I-123-interleukin-2 scintigraphy for in vivo assessment of intestinal mononuclear cell infiltration in Crohn's disease

Activated mononuclear cells expressing interleukin-2 (IL2) receptors (IL2-Rs) heavily infiltrate the Crohn's disease (CD) gut wail. A new technique for the in vivo detection of tissue infiltrating IL2-R positive (IL2R+ve) cells was developed based on I-123-IL2 scintigraphy. The aim of this study was to investigate whether (123I)-IL2 accumulates in the CD gut wall in different phases of the disease and to evaluate the specificity of I-123-IL2 binding to activated IL2R+ve cells infiltrating the gut wall. Methods: Fifteen patients with ileal GD (10 active and 5 inactive) and 10 healthy volunteers were studied by (123I)-IL2 scintigraphy. Six patients with active CD were studied before and after 12 wk of steroid treatment. After scintigraphy, patients were followed up for 29-54 mo. Ex vivo autoradiography was performed to determine specificity of I-125-IL2 binding to IL2R+ve cells. For bowel scintigraphy, I-123-IL2 (75 MBq) was injected intravenously and gamma camera images were acquired after 1 h. Bowel radioactivity was quantified in 64 regions of interest (ROIs). Results: Autoradiography showed specific binding of I-125-IL2 to IL2R+ve mononuclear cells infiltrating the CD gut wall. Intestinal I-123-IL2 uptake assessed by the number of positive ROIs was higher in patients with active or inactive CD than in healthy volunteers (P < 0.0001 and P = 0.03, respectively) and positively correlated with the CD activity index (P = 0.01). I-123-IL2 intestinal uptake significantly decreased in patients with CD in steroid-induced remission (P = 0.03). A significant correlation was observed between the number of positive ROIs and time to disease relapse. Conclusion: I-123-IL2 accumulates in the diseased CD gut wall by specific binding to IL2R+ve cells, infiltrating the involved tissues. I-123-IL2 scintigraphy may be an objective tool for the in vivo assessment of intestinal activated mononuclear cell infiltration.