At least as far back as 1976, it was known that Crohn's might be due to a deficient local inflammatory response - since the number of neutrophils that migrate to the site of a cut on the skin are lower for Crohn's patients than for normal patients, it is very possible the disease affected wound healing, as the study below from 1981 indicates:
"Skin window tests were performed on 60 patients with Crohn's disease...and 40 healthy controls. The numbers of neutrophils that migrated into the skin window chambers were significantly lower in patients with Crohn's disease...These results suggest that the depression of neutrophil migration into skin windows that is normally observed in Crohn's disease is due to a deficient local inflammatory response. This defective inflammatory response in Crohn's disease and the consequent delay in the accumulation of neutrophils could explain granuloma formation, the high recurrence rate after surgery, and the clinical course of exacerbations and remissions." http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1419419/
Another study, published in 2006, which suggests Crohn's is due to a weak, or underactive, immune system rather than an overactive immune system:
"Crohn's disease might be due to a weak immune response...A lack of an acute inflammatory response might lead to the delay or incomplete removal of bacteria and other bowel contents from the gut characterised by Crohn's. This material then breaches the mucosal barrier, and its continued presence might provoke a huge immune reaction and secondary chronic inflammation, the researchers reasoned...They took a sample from the rectums of nine controls and six patients to see the gut's reaction to the scraping. The mucosa (or membrane) was normal in all patients at the start, but six hours after the biopsy, healthy controls had an acute inflammatory response but the patients with Crohn's did not. They produced much lower amounts of white blood cells and inflammatory mediators - with a 79% reduction in immune cells called neutrophils and a 63% reduction in interleukin 8-positive cells, in comparison with controls. Research on the small intestine gave a similar result. To check whether the response was just confined to the gut, the team did another experiment using sandpaper to breach the skin barrier. Five hours after this trauma, 13 Crohn's patients still had much lower numbers of neutrophils and interleukin 8 cells at the trauma site than controls."
http://www.newscientist.com/article/dn8759-weak-immune-response-may-cause-crohns-disease.html