Dentritic cells (DC) as antigen-presenting cells are most likely responsible for regulation of abnormal T cell activation in Crohn's disease (CD), a chronic inflammatory bowel disease. We have analyzed the expression of activation and maturation markers on DC in the colon mucosa from patients with CD compared with normal colon, using immunohistochemical techniques. We found two distinct populations of DC present in CD patients: a DC-specific ICAM-3 grabbing non-integrin (DC-SIGN)(+) population that was present scattered throughout the mucosa, and a CD83(+) population that was present in aggregated lymphoid nodules and as single cells in the lamina propria. In normal colon the number of DC-SIGN(+) DC was lower and CD83(+) DC were detected only in very few solitary lymphoid nodules. Co-expression of activation markers and cytokine synthesis was analyzed with three-color confocal laser scanning microscopy analysis. CD80 expression was enhanced on the majority of DC-SIGN(+) DC in CD patients, whereas only a proportion of the CD83(+) DC co-expressed CD80 in CD as well as in normal tissue. Surprisingly, IL-12 and IL-18 were only detected in DC-SIGN(+) DC and not in CD83(+) DC. A similar pattern of cytokine production was observed in normal colon albeit to a much lesser extent. The characteristics of these in-situ-differentiated DC markedly differ from the in-vitro-generated DC that simultaneously express DC-SIGN, CD83 and cytokines.