Quantification of epidermal cell populations in the centre and margin of stable psoriatic plaques

The histological picture of psoriasis has been studied extensively. Several authors have investigated the differences between the centre and the margin of spreading plaques, because the margin is of great pathogenic interest as lesions enlarge by centrifugal expansion. However, little is known about the differences between the centre and the margin of stable plaques. In the present study we investigated quantitatively the differences between the centre and margin of stable psoriatic plaques with respect to differentiation, inflammation and proliferation. To quantify these parameters, we used flow cytometry. From nine patients with nonspreading, stable psoriasis, we obtained punch biopsies from the centre and from the lesional margin of a plaque, and performed a flow cytometric assessment, using the markers keratin 10 for differentiation, vimentin for inflammation, and TO-PRO-3 iodide for proliferation. We found that the quantitative parameters showed a large interindividual variability, and that there was no significant difference in the quantitative parameters for inflammation and proliferation between the centre and margin of stable plaques. However, the percentage of differentiated cells was significantly higher in the margin than in the centre. We conclude that there is a great heterogeneity within stable psoriatic plaques with respect to differentiation, inflammation and proliferation, but further quantitative studies are needed to substantiate the pathogenic relevance of the significant difference in keratinization between the centre and the margin of stable psoriatic plaques.