Arachidonic acid and LTB4 enhance aggregation of psoriatic peripheral blood mononuclear leukocytes in vitro

The aim of the reported series of experiments was to examine the possible role played by arachidonic acid (Aa) derivatives in monocyte aggregation in psoriasis. Twenty patients with active plaque-type psoriasis covering not less than 20% of body surface area and 20 age-matched controls were investigated. Peripheral blood monocytes were harvested according to the technique recently set up by Colotta et al. These preparations usually contained more than 95% monocytes, as assessed by morphology and esterase staining. Aggregation tracings were plotted using a common platelet aggregation recorder system and expressed in arbitrary units. Aa sodium salt, acetylsalicylic acid (ASA), indomethacin, nordihydroguaiaretic acid (NDGA), and leukotriene B4 (LTB4) were used during testing. Aa induced an enhanced aggregation of mononuclear leukocytes (MNL) in psoriatic patients versus normal controls in a concentration-dependent way. Furthermore, neither ASA nor indomethacin inhibited Aa aggregation, while both markedly increased the aggregation response in psoriasis. LTB4 induced an enhancement aggregation in psoriasis, whereas NDGA strongly inhibited it. Although the pathophysiological significance of MNL aggregation described here remains obscure, assembly of the cells at the site of psoriatic skin might be a crucial event.