Cell surface C-type lectins are implicated in many aspects of immunity. For example, professional phagocytes utilise cell surface C-type lectins in pathogen recognition/binding and phagocytosing the pathogens for destruction and/or antigen processing (e.g. mannose receptor, DC-SIGN, dectin-1). Some C-type lectins are involved in cell-cell adhesion and trafficking of leukocytes (e.g. selectins). DCL-1 is a small type I transmembrane C-type lectin receptor, discovered as a genetic fusion partner of DEC-205. DCL-1 protein was highly conserved amongst the human, mouse and rat orthologs. The human DCL-1 gene, composed of 6 exons, was located to a cluster of type I transmembrane C-type lectin genes on chromosomal band 2q24. Multiple expression array, RT-PCR and FACS analysis using new anti-hDCL-1 mAbs established that DCL-1 expression in leukocytes was restricted to monocytes, macrophages, granulocytes and DC, although DCL-1 mRNA was present in many tissues. Stable hDCL-1 CHO cell transfectants endocytosed FITC-conjugated anti-hDCL-1 mAb rapidly (t1/2 = 20 min) and phagocytosed anti-hDCL-1 mAb-coated microbeads, indicating that DCL-1 may act as an antigen uptake receptor. However, anti-DCL-1 mAb-coated microbead binding and subsequent phagocytic uptake by macrophages was ∼8-fold less efficient than that of anti-macrophage mannose receptor (MMR/CD206) or anti-DEC-205/CD205 mAb-coated microbeads. Confocal studies showed that DCL-1 colocalized with F-actin in filopodia, lamellipodia and podosomes in macrophages and the colocalization was not affected with cytochalasin D, whereas the MMR/CD206 and DEC-205/CD205 did not colocalize with F-actin. Furthermore, DCL-1-EGFP transiently expressed in COS-1 cells colocalized with F-actin at cellular cortex and microvilli. These data suggest that hDCL-1 is an unconventional lectin receptor that plays roles not only in endocytosis/phagocytosis, but also in myeloid cell adhesion and migration.

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