Lytic CD8⁺ T cells at the psoriasis plaque’s epidermis secrete IL-17, IL-21 and IL-22 and depends on autocrine TNFalpha production.

IL-17-producing CD4⁺ T lymphocytes (Th17) are currently considered relevant participants in the pathogenesis of psoriasis skin lesions. However, little is known about the potential role of IL-17-producing CD8⁺ T cells, which are also present at the psoriatic plaque. We have addressed the functional characterization of this CD8⁺ subtype of T lymphocytes from psoriasis patients. Our results show that CD8⁺IL-17⁺ cells from psoriasis-inflamed skin tissue produce TNF-α and IFN-γ (Th1-related cytokines) as well as IL-17, IL-21, and IL-22 (Th17-related cytokines) efficiently. A significant up-regulation of the RORC transcription factor is also observed. These cells are refractory to Tregs but show a proliferative response to anti-CD3/CD28 stimulation that is enhanced by IL-12 and IL-15. Blocking of TNF-α activity inhibits TCR-mediated activation and IL-17 production. CD8⁺IL-17⁺ T cells are cytotoxic cells that display TCR/CD3-mediated cytotoxic abilities to kill target cells. Thus, CD8⁺IL-17⁺ T cells share some key features with Th17 cells and exhibit remarkable differential abilities attributable to the CD8⁺ lineage of T lymphocytes, adding new insights into the functional resources of IL-17-producing cells from human epidermis that could be of potential interest to our understanding of the pathogenesis of psoriasis.