INCREASED MACROPHAGE SUBSET IN INFLAMMATORY BOWEL-DISEASE - APPARENT RECRUITMENT FROM PERIPHERAL-BLOOD MONOCYTES

Mucosal specimens from active Crohn's disease (ileum, n=6; colon, n=6), active ulcerative colitis (n=9), normal ileum (n=6), and normal colon (n=6) were subjected to paired immunofluorescence staining for characterisation of macrophage subsets in sit-a. In the normal state, only few CD68+ macrophages (<10%) expressing the myelomonocytic L1 antigen (calprotectin) were seen. In inflamed mucosa, especially near small vessels, the CD68(+)L1(+) fraction increased with the degree of inflammation, near ulcers to median 65% (range 35-91%). Cells reactive with the monoclonal antibody RFD7 were also increased in inflammation but less than 5% of them costained for L1 antigen. It is concluded that L1 producing macrophages are distinct from the RFD7(+) subset and probably recently recruited from peripheral blood monocytes. Like granulocytes, L1(+) macrophages may be important in non-specific defence, providing calprotectin with putative anti-microbial and anti-proliferative properties.