Comparison of the carbohydrate preference of SIGNR1 as a phagocytic receptor with the preference as an adhesion molecule.

C-type lectin receptors expressed on cell surfaces of antigen-presenting cells can serve as not only cell adhesion molecules but also as phagocytic receptors, and therefore, are potentially useful for antigen targeting for vaccination. In the present study, we compared the carbohydrate preference of the C-type lectin SIGNR1 as a cell adhesion molecule with that of SIGNR1 as a phagocytic receptor, using a series of neoglycolipids (NGLs) and the mouse macrophage-like cells stably expressing SIGNR1. When SIGNR1-mediated cell adhesion was assessed based on the binding of the cells to NGL-coated solid phases, the order of degree of cell adhesion was Le(b)-≈Le(a)-≈Le(x)-≥Man5->Man3-≥α1-3Man2->α1-6Man2-DPPE. By contrast, when SIGNR1-mediated phagocytosis was assessed based on the uptake of NGL-coated liposomes, the order of phagocytosis of the liposomes by the cells was Le(a)-≈Man3->Man5-≈α1-3Man2->Le(x)->Le(b)->α1-6Man2-DPPE. Collectively, SIGNR1 mediates cell adhesion to Lewis blood group antigen-containing NGL-coated solid phases more preferably than those coated with terminal mannose-containing NGLs, but mediates the phagocytosis of the Man3-DPPE- and Le(a)-DPPE-coated liposomes most preferably among the tested NGLs. Thus, the subtle carbohydrate preference of SIGNR1 on the cell surface is altered depending on the function, and the preferable carbohydrate for phagocytosis elucidated using NGL-coated liposomes might be used as the appropriate targeting signals for antigen delivery.

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