Dendritic cells and scavenger macrophages in chronic inflammatory bowel disease.

We used enzyme (acid phosphatase [AP]) and immunohistochemical techniques and a set of monoclonal antibodies (CD11, CD5, CD4, CD19, CD8, OKIa), including two recently developed antibodies--for example, HECA-452 (specific for an adhesion molecule on high endothelial venules) and RFD1 (specific for 'active' human dendritic cells) to analyse the composition of the gut wall infiltrate of 10 well defined cases of chronic inflammatory bowel disease (CIBD) (six Crohn's disease (CD), four ulcerative colitis (UC]. Two polar forms in a spectrum of gut mononuclear phagocyte types (CD11+) were identified: at the one extreme scavenger macrophages with blunted projections (AP+, Heca-452-, RFD1-) and at the other extreme, dendritic cells with long dendritic cytoplasmic projections (AP-, Heca-452+, RFD1+). Dendritic cells were mainly found in highly organised lymphoid tissue present at the deeper layers in the gut wall (normal gut: underneath the muscularis mucosae and T-cell areas of lymph follicles [25-30 per follicle]; surrounding the broad zone of scavenger macrophages at the bottom of ulcers (CIBD) and fissures (CD) and in the lymphoid aggregates [25-30 dendritic cells per aggregate] adjacent to granulomas (CD]. These observations can be taken as evidence that exaggerated antigen handling and presentation and stimulation of the immune response takes place at these foci. The observation that scavenger macrophages were localised more superficial, as band like zones (normal gut: subepithelial; mainly surrounding ulcers (CIBD) and fissures (CD] can be taken as evidence that at these spots the ingestion and degradation of foreign material takes place.