Alterations of the intestinal mucosal block in ulcerative colitis and Crohn's disease--immunological and ultrastructural findings, and considerations of the pathogenesis.

The intestinal mucosa is the very site of the chronic inflammatory lesion in ulcerative colitis (UC) and in Crohn's disease (CD). The lamina mucosa together with its own and associated cellular and humoral protective properties can be described as the mucosal block which is functionally related to the intestinal and systemic immune system. Deteriorations of this mucosal block probably are of pathogenetic significance in UC and CD. This paper will summarize observations on the systemic immune system and local immune phenomena and their possible relations to the tissue injury in the gut. An immunopathogenetic concept intends to explain the chronicity of the diseases: epithelial insufficiencies of the mucosal block are followed by strong antigenic intrusion and stimulation of the local immune system with disturbance of the local immune homeostasis and the formation of immune complexes. The interactions of phagocytes with immune complexes cause the release of degrading lysosomal enzymes, which leads to continuous injury of the mucosal block and therefore to a perpetuation of the disease.