Psoriasis is triggered by several stimuli that share a systemic production of interferon (IFN)-γ and other inflammatory mediators, which are key to regulate the production of matrix metalloproteinase (MMP)-9 and its inhibitor (TIMP)-1 by cells of monocytic lineage. This study evaluates the effect of the sera of 55 patients with psoriasis and 41 non-psoriatic individuals on the production of MMP-9 and TIMP-1 in cultured monocytes from a single healthy blood donor and in U937 cells. The effect of IFN-γ stimulation was also evaluated. Serum and supernatant concentrations of IFN-γ, MMP-9, and TIMP-1 were measured by enzyme-linked immunoassays, and the MMP-9/TIMP-1 ratios were calculated. In monocytes, incubation with psoriasis' sera increased the production of MMP-9 and TIMP-1 in comparison with both baseline and monocytes incubated with non-psoriatic sera. Although the MMP-9/TIMP-1 ratio was significantly higher compared to the baseline, no differences between groups were observed. In contrast, IFN-γ stimulation in monocytes previously exposed to psoriasis' sera increased MMP-9 levels and decreased TIMP-1 levels, whereas stimulation in monocytes exposed to non-psoriatic sera did not further modify the levels of MMP-9 or TIMP-1. Consequently, the MMP-9/TIMP-1 ratio in cells exposed to psoriatic serum was significantly higher than in cells exposed to non-psoriatic sera (24.5 versus 16.7; P < 0.05). Similar results were observed in U937 cells. Therefore, our results suggest that soluble mediators in psoriatic sera may enhance the proteolytic phenotype of monocytes when stimulated with IFN-γ, which supports the existence of a primed state in the inflammatory cells of patients with psoriasis.
Keywords: Interferon gamma; metalloproteases; psoriasis.