Digital image analysis for the evaluation of the inflammatory infiltrate in psoriasis

Traditionally the evaluation of the cellular infiltrate and protein expression in skin tissue sections is done by manual quantification. However, for reliable evaluation of histology in the development of new anti-psoriatic treatments there is a need for a more time-efficient and reproducible method. To test the use of digital image analysis (DIA) in this situation we compared the assessment of immunohistochemically stained skin sections with the more traditional manual quantification (MQ) and semi-quantitative analysis (SQA). The number of CD3⁺ T cells and the expression of E-selectin were evaluated in stained paired skin biopsies from 11 patients with chronic plaque psoriasis before and after initiation of anti-psoriasis therapy. We observed significant correlations between MQ and DIA for the number of T cells (epidermis: r=0.88, P≤0.01, dermis r=0.87, P≤0.01). Both DIA and MQ were equally effective in detecting reductions of T-cell numbers in active-treated patients. MQ took 20 h, compared to 6 h for DIA. We also observed significant correlations between SQA and DIA for the expression of E-selectin (r=0.88, P≤0.01), although DIA was more sensitive than SQA to detect (early) changes. SQA took 10 h, compared to 4 h for DIA. In conclusion, the quantification of the inflammatory infiltrate in psoriatic lesional skin by DIA generated similar results as MQ and SQA in a reliable, reproducible and higher time efficient fashion.