IL-17 was identified from a CD4+ T cells DNA library. IL-17 can be induced from primary peripheral blood CD4+ T cells upon stimulation. The cytokine exhibits a high degree of amino acid identity with HVS13, an open reading frame from a T lymphotropic Herpesvirus saimiri and with murine CTLA8. Supernatant from cells transfected with IL-17 induced IL-16 and IL-18 production and enhanced the surface expression of the intracellular adhesion molecule-1 (ICAM-1) in human fibroblasts. IL-17 is a disulfide-linked homodimer of two 31.0 kDa subunits, each containing 136 amino acid residues.