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Previous studies have shown that scale from lesional psoriatic skin contains substantial amounts of platelet activating factor (PAF). In this study, PAF and its immediate precursor, lyso-PAF, were measured in exudates from abrasions on lesional and uninvolved psoriatic skin, and from skin of healthy subjects. The mean amounts of PAF recovered from lesional and uninvolved psoriatic skin (n = 13) and from healthy skin (n = 14) were not significantly different (range 0.05-2.14 pmol/sample). Mean recoveries of lyso-PAF from lesional psoriatic skin (n = 9) and skin of healthy subjects (n = 13) were also similar (9.5 +/- 1.9 and 11.0 +/- 1.9 pmol/sample, respectively), but significantly less lyso-PAF was found in exudates from the uninvolved psoriatic skin (n = 9; 3.1 +/- 0.4 pmol/sample; P0.01 relative to both lesional psoriasis and healthy skin). The finding of reduced lyso-PAF in uninvolved psoriatic skin was unexpected because increased phospholipase-A2 activity is associated with psoriasis. These results do not support the hypothesis that extracellular PAF contributes significantly to the inflammation associated with psoriasis.

The extent of PAF synthesis and its role in inflammatory skin disorders are not known. Skin exudates were collected from suction blisters or bbrasions on healthy and inflamed human skin and analysed by gc-ms. The mean PAF andlyso-PAF values for skin of healthy subjects were 1.86±0.92 (n=7) and 160±21 (n=8) nM, respectively, in suction blister exudates, and 0.38±0.08 (n=14) and 11.0±1.9 (n=13) pmol/abrasion, respectively. PAF levels were not altered in psoriasis, nickel contact dermatitis, delayed pressure urticaria, mastocytosis or immediate and late phase reactions to antigen. Significantly, lesslyso-PAF was found in uninvolved skin of psoriasis. Increasedlyso-PAF was found in nickel contact dermatitis compared with untreated skin of the same subjects or skin or normal healthy volunteers. We conclude that, if PAF is a significant mediator of inflammation in human skin, it may remain associated with the synthesising cell or act in its immediate proximity.