Background: Antibodies against tumor necrosis factor represent an effective therapy for patients with inflammatory bowel disease. Despite their successful results, the exact mechanism by which infliximab suppresses intestinal inflammation is still a matter of debate. In this study, we used a translational approach to identify the key mechanisms associated with resolution of mucosal inflammation induced by infliximab.
Methods: A total of 16 patients with active inflammatory bowel disease (9 with Crohn's disease and 7 with ulcerative colitis) and 16 controls were enrolled in the study. Patients received infliximab infusions at 0, 2, and 6 weeks. At enrollment and at week 6, patients underwent flexible sigmoidoscopy, and biopsies were taken from the sigmoid colon. RNA was extracted, and mucosal expression of 96 immune-related genes was evaluated by qRT-PCR and confirmed by immunofluorescence microscopy on tissue. Correlation between infliximab-induced gene expression modulation and endoscopic response to therapy was calculated. Lamina propria mononuclear cell apoptosis induced by infliximab was evaluated on tissue sections by the terminal deoxynucleotidyl transferase dUTP nick end labeling assay.
Results: We found that infliximab-induced downregulation of macrophage and Th17 pathway genes was significantly associated with both endoscopic response to the therapy and achievement of mucosal healing. Importantly, the observed reduction of lamina propria CD68+ macrophages was associated with an increased rate of macrophage apoptosis.
Conclusions: The 2 mechanisms associated with infliximab-induced resolution of intestinal inflammation are the reduction of lamina propria infiltrating CD68+ macrophages and the downregulation of interleukin 17A. Moreover, the data suggest that infliximab-induced macrophage apoptosis may represent a key mechanism for the therapeutic success of anti–tumor necrosis factor antibodies.
Article first published online 27 February 2013
*Unit of Gastroenterology II, Fondazione IRCCS Ca’ Granda-Ospedale Maggiore Policlinico, Milan, Italy
†Department of Medical, Surgical and Transplantation Pathophysiology, University of Milan, Milan, Italy
‡Department of Immunology
§Department of Genomics and Molecular Biology, INGM-National Institute of Molecular Genetics, Milan, Italy
||Unit of Pathology, Fondazione IRCCS Ca’ Granda-Ospedale Maggiore Policlinico, Milan, Italy
¶Department of Dermatology, IRCCS Istituto Ortopedico Galeazzi, Milan, Italy
**Department of Internal Medicine, University of Rome “Tor Vergata”, Rome, Italy.
Reprints: Eva Reali, PhD, INGM Fondazione Istituto Nazionale di Genetica Molecolare, via Francesco Sforza 28, 20122 Milan, Italy (e-mail: firstname.lastname@example.org).
Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (http://www.ibdjournal.org).
Dr Reali is now with the IRCCS-Istituto Ortopedico Galeazzi, Milan, Italy.
The work was partially funded by INGM and supported by a research grant from MSD and by Italian fiscal contribution “5×1000” 2010 devolved to Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico.
F. Caprioli and F. Bosè contributed equally to this work.
The authors have no conflicts of interest to disclose.
Received July 13, 2012
Accepted July 16, 2012