DECREASED CD11B EXPRESSION ON CIRCULATING POLYMORPHONUCLEAR LEUKOCYTES IN PATIENTS WITH EXTENSIVE PLAQUE PSORIASIS

In psoriasis, polymorphonuclear leukocytes are consistently present in the early psoriatic lesion and in actively spreading plaques. CD11b, which is part of the beta 2-integrin receptor Mac-1, plays an importan t role in various biological functions of the polymorphonuclear leucoc yte such as leukocyte adhesion to endothelium, extravasation, tissue m igration and degranulation. In the present study we investigated the p ossibility of systemic differences in leukocyte CD11b-expression betwe en patients with extensive plaque psoriasis and healthy volunteers. Ve nous blood samples were obtained from 15 patients with extensive plaqu e psoriasis (Psoriasis Area and Severity Index greater than 10.0), and from 15, matched, healthy controls. Both unstimulated and in vitro le ukotriene B-4-stimulated leukocytes were stained for CD11b, which was quantified using flow cytometry methods. A tendency towards decreased basal CD11b expression was observed on leukocytes from psoriatic patie nts compared to healthy subjects. After in vitro stimulation with leuk otriene B-4 (LTB4), the difference between psoriasis patients and cont rols increased further and was statistically significant. Patients wit h unstable psoriasis (increasing size of individual lesions and/or pin point papules around chronic plaques) proved to have even lower unstim ulated and LTB4-stimulated CD11b expression. No correlation relation w as found between CD11b expression and severity of psoriasis using the PASI-score. Interestingly, the relative CD11b up-regulation (ratio CD1 1b(LTB4stimulated)/CD11b(unstimulated)) was virtually the same in both groups. Therefore, the signalling pathway from leukotriene B-4-recept or binding up to CD11b expression on the leukocyte surface, was essent ially normal in psoriasis. It is hypothesised that the decreased CD11b expression in psoriasis patients is caused by leukocyte compartmental isation.