Comparison of weal and flare responses to platelet activating factor (PAF)and histamine, and the ultrastructural effects of PAF in the skin of atopic and normal subjects

Weal volume and flare area responses to intradermal platelet activating fac tor (PAF) and histamine, both in the presence and absence of the protein ca rrier, human serum albumin (HSA), were measured in the skin of normal subje cts, atopics without dermatitis, and in the normal-appearing skin of patien ts with atopic dermatitis. The ultrastructural effects of intradermal PAF w ere also studied in the same groups of subjects. Weal and flare dose-respon ses to PAF were enhanced by the presence of human serum albumin, HSA itself producing a significantly greater mean weal response in each group than ly so-PAF (P<0.01). However, comparison of normal subjects, atopics without de rmatitis and patients with atopic dermatitis, showed the differences in dos e-response effects of PAF and histamine on weal volume and flare area to be nonsignificant. The cellular respsonse to PAF in normal subjects and atopi cs consisted predominantly of neutrophil extravasation; eosinophils were no ted in the normal-appearing skin of atopics and patients with atopic dermat itis 30min and 4h after injection. At an ultrastructural level PAF induced opening of endothelial gaps and extravasation of neutrophils in each group.