Fig. 4From: Inducible Nitric Oxide Synthase and Proinflammatory Cytokine Expression by Human Keratinocytes during Acute Urticaria Proposed scheme of intercellular interactions in the skin during acute urticaria IL-4 is synthesized and released from dermal mast cells and induces expression of CD23 (FcεRII) at the surface of keratinocytes. IgE/allergen immune complexes can trigger FcεRI on mast cells, leading to the release of histamine, and CD23 on keratinocytes, leading to the release of proinflammatory cytokines (TNF-α, IL-6). This process takes place in part because of nitric oxide metabolism. Along with histamine and other vasoactive mediators, NO can also contribute toward the vasodilatation of dermal microvasculature (+, stimulatory signals).Back to article page