SUMMARYFicolins are a group of multimeric proteins that contain collagen-like and ®brinogen-like (FBG) sequences. Three types of ®colins have been characterized: H-, L-and M-®colins. Both H-and L®colins have demonstrated lectin activities. In the present study, the FBG domain of M-®colin was expressed and shown to bind to N-acetyl-D-glucosamine. M-®colin mRNA was expressed in monocytes but not in the more differentiated macrophages and dendritic cells. By¯ow cytometry, surface biotinylation and immunoprecipitation, we showed that M-®colin was associated with the surface of promonocytic U937 cells. M-®colin transiently expressed in COS-7 cells was also clearly detected on the cell surface by immunoprecipitation. By¯ow cytometry, M-®colin was detected on peripheral blood monocytes but not on lymphocytes or granulocytes. Immobilized rabbit anti-M®colin F(abk) 2 mediated U937 cell adhesion, and the antibody also inhibited phagocytosis of Escherichia coli K-12 by U937 cells. Therefore, M-®colin might act as a phagocytic receptor or adaptor on circulating monocytes for micro-organism recognition and may potentially mediate monocyte adhesion.