It's possible that the symptomatic pain relief from TNF-alpha blockers is primaly from the decreased pain signaling in the brain.
It's never been researched in crohn's disease afaik, but that's what happen in RA patients, they get pain relief long before MRI shows any changes to bone inflammation.
People seem to forget that TNF-alpha doesn't just direct inflammation, it directs pain. You can have a very inflamed intestine but if you block certain cytokine you can stop pain signaling to the brain, even though the intestine could still be very inflamed. It's possible that this is happening in crohn's disease. Humira might be both blocking the pain signaling and inflammation.
It's certain that humira helps control the intestinal inflammation in people, but I always had my doubts that when people get quick relief after humira or infliximab, that it's related to intestinal relief, colonoscopies show it takes weeks before the intestine is fully healed when people go on TNF-alpha blockers, the immediate relief could very well be from decreased pain signaling to the brain because of decreased TNF-alpha.