At the protein level, human IL-17+ CD8+ T cells express several surface markers, although as yet no markers have been defined that are exclusively expressed on these cells. The majority of cultured IL-17+ CD8+ T cells isolated from active psoriatic plaques were found to express CD161 . Furthermore, CD8+ T cells isolated from liver biopsies of patients with chronic HCV infection were found to co-express CD161 and IL-17 after ex vivo stimulation , which was also observed ex vivo in stimulated CD3+ CD4- IL-17+ T cells from the joints of patients with psoriatic arthritis . CD161 has been shown to be a marker of CD4+ IL-17+ T lymphocytes, however it does not represent a definitive marker for IL-17+ T cells as not all CD161+ cells produce IL-17 .