Mast cells participate in allergies, and also in immunity and inflammation by secreting proinflammatory cytokines. Flavonoids are naturally occurring polyphenolic plant compounds, one group of which – the flavonols, inhibits histamine and some cytokine release from rodent basophils and mast cells. However, the effect of flavonols on proinflammatory mediator release and their possible mechanism of action in human mast cells is not well defined. Human umbilical cord blood‐derived cultured mast cells (hCBMCs) grown in the presence of stem cell factor (SCF) and interleukin (IL)‐6 were preincubated for 15 min with the flavonols quercetin, kaempferol, myricetin and morin (0.01, 0.1, 1, 10 or 100 μM), followed by activation with anti‐IgE. Secretion was quantitated for IL‐6, IL‐8, tumor necrosis factor‐alpha (TNF‐α), histamine and tryptase levels. Release of IL‐6, IL‐8 and TNF‐α was inhibited by 82–93% at 100 μM quercetin and kaempferol, and 31–70% by myricetin and morin. Tryptase release was inhibited by 79–96% at 100 μM quercetin, kampferol and myricetin, but only 39% by morin; histamine release was inhibited 52–77% by the first three flavonols, but only 28% by morin. These flavonols suppressed intracellular calcium ion elevations in a dose–response manner, with morin being the weakest; they also inhibited phosphorylation of the calcium‐insensitive protein kinase C theta (PKC θ). Flavonol inhibition of IgE‐mediated proinflammatory mediator release from hCBMCs may be due to inhibition of intracellular calcium influx and PKC θ signaling. Flavonols may therefore be suitable for the treatment of allergic and inflammatory diseases. British Journal of Pharmacology (2005) 145, 934–944. doi:10.1038/sj.bjp.0706246

Stress activates the hypothalamic-pituitary-adrenal axis through CRH, leading to production of glucocorticoids that down-regulate immune responses. However, acute stress also has proinflammatory effects. We previously showed that restraint stress, as well as CRH and its structurally related urocortin (Ucn), could activate mast cells and trigger mast cell-dependent vascular permeability. Here we show for the first time that human cord blood-derived cultured mast cells (hCBMC) at 10 wk, but not at 2 wk, are immunocytochemically positive for CRH and Ucn; human leukemic mast cells are weakly positive for both peptides. The ability of these mast cells to synthesize CRH and Ucn was confirmed by showing mRNA expression with RT-PCR. hCBMC (8–14 wk) synthesize and store 1–10 ng/10⁶ cells (10–20 μg/g) of both CRH and Ucn detected by ELISA of cell homogenates. Stimulation of IgE-sensitized hCBMC with anti-IgE results in secretion of most CRH and Ucn. These findings indicate that mast cells are not only the target, but also a potential source of CRH and Ucn that could have both autocrine and paracrine functions, especially in allergic inflammatory disorders exacerbated by stress.

Stress induces CRH secretion that activates hypothalamic-pituitary-adrenal axis and is also abortogenic. In addition to hypothalamus, CRH and its analog urocortin (Ucn) are also secreted locally outside the brain where they activate mast cells leading to inflammation; however, the level of CRH and Ucn or mast cell mediators has not been examined in products of conception (POC). CRH and Ucn were measured by enzyme immunoassay, tryptase by fluoroenzyme immunoassay, and IL-8 by ELISA in POC of 7-9 wk gestation from Caucasian women; they were divided into group I with elective abortions (n = 4), group II with one spontaneous abortion (n = 12), and group III with at least two spontaneous abortions (n = 7). CRH, Ucn, tryptase, and IL-8 levels were higher (P < 0.05) in group III (8683 ± 1201 pg/g, 7961 ± 1499 pg/g, 1553 ± 572 ng/g, and 8317 ± 1874 pg/g, respectively) than group II (2561 ± 314 pg/g, 2349 ± 394 pg/g, 403 ± 97 ng/g, and 3199 ± 449 pg/g, respectively) and group I (163 ± 162 pg/g, 328 ± 327 pg/g, 72 ± 31 ng/g, and 3681 ± 931 pg/g, respectively). Immunostaining of POC showed significantly more tryptase in group III women. High POC levels of CRH and Ucn under stress in habitual spontaneous abortions may activate uterine mast cells to secrete abortogenic tryptase and IL-8.