Lectin activities of cytokines: functions and putative carbohydrate-recognition domains

The discovery that some cytokines have carbohydrate-binding (lectin) properties opens new concepts in the understanding of their mechanism of action. The carbohydrate-recognition domain (CRD), which is localized at the opposite of the receptor-binding domain, makes these molecules bi-functional. The expression of the biological activity of the cytokine relies on its carbohydrate-binding activity, which allows the association of the cytokine receptor with molecular complexes comprising the specific kinase/phosphatase involved in receptor phosphorylation/dephosphorylation and in specific signal transduction. As a correlate, a cytokine can act only on cells possessing both the receptor and the ligand. Two cytokines using the same receptor can have different target cells and functions because of their different lectin activities. Based on a few examples, the CRD can be predicted based on the 3-D structures of the molecules.