CD4 and collagenous colitis: We found that despite the subtle inflammation in the mucosa of collagenous colitis patients, not visible by the naked eye upon colonoscopy, soluble factors in the mucosa are sufficient to significantly enhance the production of IFN-γ, IL-17A, IL-6, IL-1β, IL-4, and IL-10 by peripheral CD4+ T cells exposed to them in vitro.