IL-17 Expression Negatively Correlates with γδ T-Cell Accumulation in Human Psoriasis Lesions: A Novel Implication for Disease Pathogenesis

Psoriasis, an inflammatory autoimmune disease, arises from intricate interactions between the immune system and epithelium. Recent reports have suggested new roles for gamma delta (γδ) T-cells in addition to immune surveillance, however, it remains to be determined whether the mechanisms identified in psoriasis murine models have a similar role in humans. The present study aimed to examine the relationship between IL-17 mRNA level and the γδ T-cell proliferation and to clarify their function in the psoriatic human samples. The study involved 20 patients diagnosed with psoriasis and 16 control subjects. Expression of the IL-17 gene was measured in formalin-fixed paraffin-embedded (FFPE) tissues by qRT-PCR method. TCRγδ ⁺ immunofluorescence staining was performed to measure the proliferation and distribution of γδ T-cells in the same samples. In psoriatic lesion biopsies, TCRγδ ⁺ T-cell percentage was found higher than the control samples. Additionally, psoriasis patients exhibited elevated levels of IL-17 gene expression. In addition, this study showed a weak negative correlation between γδ T-cell proliferation and IL-17 gene expression in psoriatic skin samples, highlighting the novel effector functions of these cells in psoriasis pathogenesis.