Background: Allergic airway diseases are more common in females than in males during early adulthood. A relationship between female hormones and asthma prevalence and severity has been suggested, but the cellular and molecular mechanisms are not understood.
Objective: To elucidate the mechanism(s) by which estrogens enhance the synthesis and release of mediators of acute hypersensitivity.
Methods: Two mast cell/basophil cell lines (RBL-2H3 and HMC-1) and primary cultures of bone marrow derived mast cells, all of which naturally express estrogen receptor-alpha, were examined. Cells were incubated with physiological concentrations of 17-beta-estradiol with and without IgE and allergens. Intracellular Ca(2+) concentrations and the release of beta-hexosaminidase and leukotriene C(4) were quantified.
Results: Estradiol alone induced partial release of the preformed, granular protein beta-hexosaminidase from RBL-2H3, BMMC and HMC-1, but not from BMMC derived from estrogen receptor-alpha knock-out mice. The newly synthesized LTC(4) was also released from RBL-2H3. Estradiol also enhanced IgE-induced degranulation and potentiated LTC(4) production. Intracellular Ca(2+) concentration increased prior to and in parallel with mediator release. Estrogen receptor antagonists or Ca(2+) chelation inhibited these estrogenic effects.
Conclusion: Binding of physiological concentrations of estradiol to a membrane estrogen receptor-alpha initiates a rapid onset and progressive influx of extracellular Ca(2+), which supports the synthesis and release of allergic mediators. Estradiol also enhances IgE-dependent mast cell activation, resulting in a shift of the allergen dose response.