Decreased expression levels of L‐selectin on subsets of leucocytes and increased serum L‐selectin in severe psoriasis

L‐selectin is a leucocyte adhesion molecule involved in leucocyte interactions with vascular endothelial cells. Following leucocyte activation L‐selectin is endoproteolytically released from the cell surface. To assess whether psoriasis vulgaris results in systemic leucocyte activation, we examined expression levels of L‐selectin on subsets of peripheral blood leucocytes from patients with psoriasis (n = 25) and normal control subjects. Serum levels of soluble L‐selectin were quantified by ELISA in patients with psoriasis (n = 75), pustulosis palmaris et plantaris, and contact dermatitis, as well as normal control subjects. Psoriasis severity was evaluated by psoriasis area and severity index (PASI). L‐selectin expression levels on CD4+ T cells, B cells, monocytes, and neutrophils from patients with severe‐type psoriasis (PASI ≥ 15) was significantly decreased compared with leucocytes from normal control subjects. Furthermore, L‐selectin expression on CD4+ T cells showed good inverse correlation with PASI scores. Monocyte L‐selectin expression was restored when the skin lesions of psoriasis were remitted. The frequencies of L‐selectin+ CD4+ T cells or L‐selectin+ CD8+ T cells from patients with psoriasis were almost normal. Serum L‐selectin levels in patients with severe‐type psoriasis were significantly higher than those in normal control subjects. These results suggest that subsets of leucocytes may be activated in psoriasis, and that L‐selectin expression levels on some leucocyte subsets, especially CD4+ T cells, tend to correlate with disease severity of psoriasis.