Inducible Co-Stimulator Ligand (ICOSLG) belongs to the immunoglobulin superfamily. ICOSLG contains Ig-like C2-type (immunoglobulin-like) domain and 1 Ig-like V-type (immunoglobulin-like) domain. ICOSLG acts as a costimulatory signal for T-cell proliferation and cytokine secretion, it also induces B-cell proliferation and differentiation into plasma cells. It could play an important role in mediating local tissue responses to inflammatory conditions, as well as in modulating the secondary immune response by co-stimulating memory T-cell function. ICOSLG is widely expressed lymph nodes, leukocytes and spleen, detected on activated monocytes and dendritic cells.