Phospholipase A2 activity of peripheral-blood mononuclear leukocytes in psoriasis.

D.I. Wilkinson, Psoriasis Research Institute, 600 Town & Country Village, Palo Alto, CA 94301 (USA) Ten years ago, Forster et al. [1] demonstrated increased phospholipase A2 (PLA2) activity in nonlesional skin of psoriasis patients [2], possibly due to downregulation of the lipocortin 1 inhibitor [3, 4] and resulting in an overly active arachidonic acid cascade [5]. The possibility of upregulated PLA2, an inflammatory mediator [6], as a phenotypic expression of psoriasis suggested a series of experiments using peripheral-blood mononuclear leukocytes (PBMLs) from control and psoriatic blood, with or without challenge. Hopefully, these experiments would suggest a noninvasive test that might be used to detect latent psoriasis in subjects as yet without clinical symptoms. Two general methods to assess PBML activity were used. Following Goppelt-Struebe [7], normal and psoriatic PBMLs were isolated using a Ficoll gradient and prelabeled with 7⁄8 arachidonic acid before exposure to one of the following: calcium ionophore A23187 (1 μg/ml), thrombin (1 μg/ml) or lipoteichoic acid (from Staphylococcus aureus; 5-100 ng/ml). Without any of these, the amount of 3⁄4 released to the supernatant by control cells was 23.1 ± 6.4% (SD; n= 15), and this figure was 67.3 ± 8.9% (n = 9) when A23187 was used or 32.5 ± 8.1 (n = 5) with thrombin; lipoteichoic acid had no effect. These figures were not significantly different when psoriatic PBMLs were used. According to Etienne and Polonovski [8], aliquots of sonicated cell suspensions were incubated with L-α-dioleoylphos-phatidyl-2-14C-ethanoIamine, followed by separation of extracted lipids by thin-layer chromatography. The distribution of l4C on the plates was monitored and quantified by ß-radiation scanning and visualization. Figure 1 shows the results with a nonenzymatic control (a), two positive controls (b) using pancreatic PLA2 ♦ Φ♦Φ♦ ψ W 3⁄8 W ¶f í é i i ► 1⁄8ÈÊ 1⁄8ÊÈ 1⁄2 a b b c Fig. 1. Separation by thin-layer chromatography of the PLA2 product lysophosphatidylethanolamine (arrow) from the substrate after treatment with pancreatic PLA2 (b) or PBML sonicates (c) or neither (a). Lipids were visualized with iodine vapor. References