Scientific Abstract

Proposal No. IBD-0193R
Principal Investigator: Anthony W. Segal, M.D., Ph.D., D.Sc.
Applicant Organization: University College London (United Kingdom)
Project Title: Impaired innate immunity and the pathogenesis of Crohn’s disease
Period of Award: March 1, 2007 – February 29, 2008

Recent research in innate immunity heralds a paradigm shift in the understanding of the etiology of Crohn’s disease (CD), suggesting that it actually represents an immunodeficiency. Our published data from patients with CD (Lancet 2006; 367: 668–78) demonstrate impaired neutrophil recruitment to sites of experimental bowel and skin injury, reduced blood-flow to sites of bacteria inoculation, and impaired macrophage function in response to bacterial stimulation (in particular, interleukin-8 (IL-8) secretion).

We therefore hypothesize that there is defective (or delayed) chemotaxis of neutrophils resulting from a combination of the phenomena listed above. Patients with CD are therefore less able to completely and quickly eliminate bacteria (or their components) from sites of infection or abnormal aggregation. In an attempt to remove the bacterial threat, excessive chronic inflammation and granuloma formation ensue; the hallmarks of CD. To test the ‘bacterial persistence’ hypothesis, we will study clearance of radio-labelled E. coli from the forearm skin of test subjects. Using a skin site may also confirm the generalized nature of such a defect.

While epithelial cells appear to play a key role in mucosal immunity (particularly in bacterial translocation), in situ hybridization (ISH) demonstrates that lamina propria macrophages are the primary source of interleukin-8 in chronically-inflamed bowel biopsies from CD patients. We will relate this observation to our hypothesis by comparing biopsies before and after bowel wall injury to localize the source of IL-8 in the ‘acute phase’ with ISH and cell-specific immunofluorescence (IF) experiments. Skin biopsies from healthy individuals will also be obtained for ISH/IF (to validate the skin ‘model’).

We will also perform assays of effector function on isolated neutrophils from CD patients to confirm our hypothesis that they are not defective in bacterial killing. If defects are demonstrated, these neutrophils will be studied in more detail biochemically.

Results from this study will lead on to further investigation and trials of therapeutic intervention, which will directly benefit patients with CD.