Urticaria and angioedema are common disorders affecting approximately 15-20% of the population at least once during their lifetime (Swinny, 1941; Sheldon et al., 1954; McKee, 1966). Urticarial lesions result from localized dilatation and transudation of fluid from small venules, and in their simplest form are thought to represent the same sort of wheal-and-flare reaction observed when histamine is injected into the skin. Clinically, one observes the presence of pruritic, erythematous cutaneous wheals that blanch with pressure, reflecting the underlying edema and dilated blood vessels. The histopathological features of urticaria are dilatation of cutaneous blood vessels and lymphatics in the superficial dermis, widening of dermal papillae, flattening of rete pegs, and swelling of collagen fibers.

http://www.fitzpatricksdermatology.com/references/Fitzpatricks_Derm8e_Ref_Ch038.pdf

Urticaria and Angioedema

https://www.jbc.org/content/262/9/4223.full.pdf

Human plasma platelet-activating factor acetylhydrolase. Purification and properties.

Reactive oxygen and ischemia/reperfusion injury of the liver.

https://www.jbc.org/content/259/19/12014.full.pdf

1-O-alkyl-2-arachidonoyl-sn-glycero-3-phosphocholine. A common source of platelet-activating factor and arachidonate in human polymorphonuclear leukocytes.

By using tritiated 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine (3H-PAF), we have directly identified its specific binding sites on rabbit platelet plasma membranes. The equilibrium dissociation constant for 3H-PAF is 1.36 (+/- 0.05) X 10(-9) M at 0 degrees C. The number of binding sites is 1.61 (+/- 0.34) X 10(12)/mg of membrane, which corresponds to approximately 150-300 receptors/platelet (depending on membrane vesicle orientation). Binding of 3H-PAF to rabbit platelet plasma membrane is rapid (t1/2 less than 5 min at 0 degrees C) and reversible. For a series of PAF analogues, their affinity for the receptor sites parallels with their relative potency to induce platelet aggregation. PAF can cause contraction of smooth muscle of heart, parenchymal strip, trachea, and ileum. Specific PAF receptor binding was demonstrated with purified plasma membrane from several smooth muscles and from polymorphonuclear leukocytes but not from presumably PAF nonresponsive cells such as erythrocytes and alveolar macrophages. It is likely that the interaction of PAF with these binding sites initiates the specific responses of platelets, polymorphonuclear leukocytes, and smooth muscles.

Specific receptor sites for 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine (platelet activating factor) on rabbit platelet and guinea pig smooth muscle membranes.

1-O-Alkyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine aggregates and degranulates platelets and polymorphonuclear neutrophils. Here, the bioactivities of this platelet-activating factor, its 2-O-ethyl, and its 2-lyso derivatives were examined further. Each phospholipid aggregated and degranulated rabbit platelets and neutrophils with relative potencies of about 10,000 1,000, and 1, respectively. For rabbit neutrophils, and 2-O-acetyl compound was active in nanomolar and lower concentrations; required extracellular calcium and magnesium in order to induce aggregation; and required extracellular calcium and cytochlasin B in order to induce optimal degranulation. Furthermore the 2-O-acetyl and 2-O-ethyl compounds, in concentrations about tenfold higher than those required for rabbit neutrophils, aggregated and degranulated human neutrophils. With reference to these human neutrophil responses, degranulation required, and aggregation was dramatically enhanced by, cytochalasin B. The lysoanalog was unable to induce these response in the human cells. Thus, these lipids represent a novel class of neutrophil stimulants that closely resemble certain chemotactic factors (eg, C5a and synthetic oligopeptides) in their ability to aggregate and degranulate neutrophils and in the influences which calcium, magnesium and cytochalasin B have on their bioactions. Because platelet-activating factor circulates in the blood of rabbits and, perhaps, humans during anaphylaxis and is suspected of being involved in other syndromes such as serum sickness, this lipid may have unique biologic significance: it may act to recruit platelets and neutrophils into the lesions of these and similar pathologic syndromes.

1-O-Alkyl-sn-glyceryl-3-phosphorylcholines: a novel class of neutrophil stimulants.

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1-O-Alkyl-sn-glyceryl-3-phosphorylcholines: a novel class of neutrophil stimulants.