Crohn's is an autoimmune disorder
This is a hypothesis that is old, never proven, and at the very least very misleading.
Crohn is now recently seen an immune deficiency state, a pathogen takes advantage of that moment where our body is in a deficiency state (stress might be a factor, NOD2 might be a factor, overhygene might be a factor, consumption of milk) , the body can't kill the pathogen on it's own, and our body overreacts, TNF-Alpha increases as a response, and you get inflammation. (many pathogens can hide inside macrophages so they're very hard to kill, this is also the reason why many think Infliximab "works", since it's killing the cells where the pathogen is hiding, but many pathogens reproduce slowly, so it keeps happening over and over until we might get to a point where we can correctly identify the pathogen, find the right antibiotics and eradicate it completely from the body)
There have been a number of studies where they "inject" crohn patients with a harmless bacteria, they do the same with a person without crohn, and they can see the patient who has crohn reacts much slower, indicating an immune deficiency.
http://www.springerlink.com/content/c313853j75872167/
"Importantly, in a recent study, Marks et al. [1] has
compared the inflammatory responses in healthy controls
with those in Crohn’s disease patients by subjecting monocyte-
derived macrophages to pro-inflammatory signals and
by quantifying neutrophil recruitment and cytokine production.
These authors employed a highly innovative
model of acute intestinal trauma (two sequential endoscopic
intestinal biopsies at the same place taken six hours
apart). Importantly, in the second biopsies, a lower cytokine
production and an abnormally low neutrophil accumulation
was observed in patients with Crohn’s disease
compared with healthy controls. It is difficult to interpret
these data in any other way than with the hypothesis that
patients who suffer from Crohn’s disease have an impaired
acute immunity."
--> this indicates immune deficiency, not at all autoimmune
There have been a number of tests like those, and they all indicate crohn patients reacts differently when a pahtogen invades their body. The crohn patients are in an immune deficiency state (innate or not, they don't know).
http://hera.ugr.es/doi/16656428.pdf
On topic: I personally think stress can contribute to the onset of crohn, I was in a very very stressful situation when I got crohn. If all of the above makes sense, then it makes sense a pathogen could exploit the moment a body is in stress.