Activated and cycling lymphocytes in benign dermal lymphocytic infiltrates including psoriatic skin lesions

Summary Single-cell DNA measurements obtained using flow cytometry have previously been used as a diagnostic tool for various malignant diseases. We used this technique to characterize the dermal infiltrates of 14 patients with psoriatic skin lesions and 22 patients with various benign skin disorders. The DNA histograms of all of the patients exhibited an increased number of cells showing propidium-iodide fluorescence in the hyperdiploid region as compared to those seen in control DNA histograms of normal blood mononuclear cells. The calculated DNA indices revealed one hyperdiploid (G₀/G₁) peak in 17 cases and two hyperdiploid (G₀/G₁) peaks in 13 cases. The results suggest that the dermal lymphocytic infiltrate consists of (1) lymphocytes in the cell-division cycle, (2) non-cycling lymphocytes (G₀) and (3) activated lymphocytes that may either remain in a non-cycling state or enter the cell cycle.