The present invention relates to the use of a compound that binds to a C-type lectin on the surface of a dendritic cell, in the preparation of a composition for modulating, in particular reducing, the immune response in an animal, in particular a human or another mammal. The composition in particular modulates the interactions between a dendritic cell and a T-cell, more specifically between a C-type lectin on the surface of a dendritic cell and an ICAM receptor on the surface of a T-cell. The compositions can be used for preventing/inhibiting immune responses to specific antigens, for inducing tolerance, for immunotherapy, for immunosuppression, for the treatment of auto-immune diseases, the treatment of allergy, and/or for inhibiting HIV infection. The compound that binds to a C-type lectin is preferably chosen from mannose, fucose, plant lectins, antibiotics, sugars, proteins or antibodies against C-type lectins. The invention also relates to such antibodies, and to a method for isolating dendritic cells using such antibodies.