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 factor (PAF) and histamine, both in the presence and absence of the protein carrier, human serum albumin (HSA), were measured in the skin of normal subjects, atopics without dermatitis, and in the normal-appearing skin of patients with atopic dermatitis. The ultrastructural effects of intradermal PAF were also studied in the same groups of subjects. Weal and flare dose-responses to PAF were enhanced by the presence of human serum albumin, HSA itself producing a significantly greater mean weal response in each group than lyso-PAF (P < 0.01). However, comparison of normal subjects, atopics without dermatitis and patients with atopic dermatitis, showed the differences in dose-response effects of PAF and histamine on weal volume and flare area to be nonsignificant. The cellular response to PAF in normal subjects and atopics consisted predominantly of neutrophil extravasation; eosinophils were noted in the normal-appearing skin of atopics and patients with atopic dermatitis 30 min and 4 h after injection. At an ultrastructural level PAF induced opening of endothelial gaps and extravasation of neutrophils in each group.