Abstract: Inducible co-stimulator（ICOS）and its ligand（ICOSL）play an important role in the response and regulation of immune system. It shows that ICOS bind to ICOSL relating to self-immune diseases and tumour. Targeted interventions of ICOS/ICOSL will provide new approaches for prevention and therapy of clinical diseases.

Key words: ICOS/ICOSL, immunomodulatory, diseases