Interleukin-19 upregulates keratinocyte growth factor and is associated with psoriasis

BACKGROUND: Interleukin (IL)-19, a member of the IL-10 family, signals through the IL-20R1/IL-20R2 heterodimer, which is shown to be involved in abnormal keratinocyte differentiation and proliferation. Little is known about its in vitro biological functions or its role in psoriasis. OBJECTIVES: To investigate the role of IL-19 in the psoriatic process. METHODS: The expression of keratinocyte growth factor (KGF) transcripts was measured by polymerase chain reaction in CD8+ T cells treated with IL-19. Next, we developed monoclonal and polyclonal antibodies to measure the levels of IL-19 in the sera of patients with psoriasis and healthy volunteers using an enzyme-linked immunosorbent assay. In addition, we performed immunohistochemical staining on psoriatic skin and normal controls. RESULTS: We found that IL-19 upregulated KGF transcripts on CD8+ T cells. Patients with psoriasis had a lower level of IL-19 in serum than healthy volunteers. The difference between these two groups was statistically significant (P < 0.05). IL-19 expression was seen in basal and suprabasal keratinocytes in a continuous pattern, and was increased in psoriatic epidermis. CONCLUSIONS: These results suggest that IL-19 plays a role in the complex pathological cytokine network in psoriasis.