The aetiology and pathogenesis of chronic inflammatory bowel disease a
re unknown. However, there is circumstantial evidence that immune mech
anisms may play a significant role in mediating the gut lesion and var
ious systemic manifestations. The role of the cellular immune system,
soluble mediators, including proinflammatory and immunoregulatory cyto
kines, humoral immunity and mucosal complement activation will be disc
ussed.