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Summary: Background: Chronic spontaneous urticaria (CSU) is an inflammatory skin disorder characterized by recurrent weals, angio‐oedema or both. Recent studies have shown that the number of endothelial cells is increased in the skin of patients with CSU, but the underlying mechanisms and clinical implications of this are unclear. Aim: To evaluate whether mast cell (MC) or endothelial cell (EC) numbers correlate with CSU and whether they are relevant for disease duration, disease activity or the presence of clinical features. Methods: We determined the numbers of CD31+ ECs and MCs in nonlesional skin of 30 patients with CSU using quantitative histomorphometry, and assessed their correlation with each other and with clinical features such as disease duration, disease activity and occurrence of angio‐oedema. Results: The numbers of MCs and ECs were high in the nonlesional skin of patients with CSU, but did not correlate with each other. Neither MC number nor EC number correlated with disease duration or disease activity. Interestingly, patients with high numbers of cutaneous CD31+ ECs had higher rates of recurrent angio‐oedema and vice versa. Conclusions: Based on these findings, we speculate that vascular remodelling and MC hyperplasia in patients with CSU occurs independently and via different mechanisms. Targeting of the mechanisms that drive neoangiogenesis in CSU may result in novel therapeutic strategies for the management of patients with angio‐oedema. [ABSTRACT FROM AUTHOR]

Background Platelet-activating factor ( PAF) causes wheal and flare responses which are abrogated by H1-antihistamines giving rise to the hypothesis that PAF-induced wheal development is secondary to histamine release from dermal mast cells. But is this hypothesis correct? Methods Wheal and flare responses were induced by intradermal injection of PAF, codeine and histamine in 14 healthy volunteers. Dermal histamine and PGD2 contractions were measured using microdialysis. Results PAF, unlike histamine and codeine, did not cause a statistically significant rise in mean histamine levels with ten persons showing negligible histamine release. Codeine caused a significant but variable histamine release, ranging from 29 to 282 ng/ml. Codeine, but not PAF or histamine, caused a small but statistically significant release of PGD2. Conclusion Wheal and flare reactions in human skin induced by PAF are not associated with histamine release and, therefore, appear to be independent of mast cell degranulation. [ABSTRACT FROM AUTHOR]