Author ORCID Identifier

Defense Date


Document Type


Degree Name

Doctor of Philosophy


Microbiology & Immunology

First Advisor

John J. Ryan


Mast cells are tissue resident, innate immune cells that provide protection against parasitic and bacterial infections and venom poisoning. Mast cells also play a pathogenic role in atopy and allergic diseases. Atopy and allergic diseases are increasing in the developed world and are predicted to continue to increase at an alarming rate. Current treatment options include corticosteroids, anti-histamines, anti-IgE and avoidance of allergen. These interventions have limitations: some patients are steroid resistant; anti-histamines have low efficacy since they need to be administered early during allergen exposure; and anti-IgE is costly. Thus there is a clinical need for new treatment options. An efficient approach is to re-purpose FDA-approved drugs. Selective serotonin reuptake inhibitors (SSRIs) are a class of anti-depressants used to treat depression and other psychiatric disorders. SSRIs have been shown to possess anti-inflammatory properties, but the mechanism of action is unclear. The possibility to treat allergic diseases with SSRIs has not been studied. Using primary mouse bone marrow derived, ex vivo cultured mouse peritoneal, and primary skin derived human mast cells, we show that the SSRI fluoxetine suppresses IgE-mediated degranulation, cytokine production, and inflammatory lipid secretion. Several other SSRIs showed similar effects on mouse mast cells. Cytokine suppression occurs at a transcriptional level, as evidenced by decreased signaling downstream of the IgE receptor and reduced cytokine mRNA induction. We found that fluoxetine-mediated suppression requires the purinergic receptor, P2X3. Furthermore, we show that IgE stimulation elicits rapid ATP release from mast cells, and that ATP and purinergic signaling is a positive feedback regulator of mast cell activation. Fluoxetine can also suppress ATP-mediated cytokine production, degranulation, and lipid production most likely via NFkb suppression and diminished purinergic receptor expression. Importantly, fluoxetine effects are consistent in an in vivo passive systemic anaphylaxis (PSA) model and in a house dust mite (HDM) airway hyperresponsiveness and lung inflammation model of asthma. In the PSA model, fluoxetine reduced hypothermia and cytokine production. In the asthma model, the drug suppressed bronchoresponsiveness as well as pulmonary mast cell hyperplasia and eosinophilia, and the recruitment of Th2 cells, neutrophils, eosinophils, and lymphocytes to the bronchoalveolar space, as well as cytokine levels in the bronchoalveolar fluid in sensitized mice. Overall, we show that fluoxetine broadly suppresses mast cell activation in vitro and in vivo, most likely by impeding an ATP-P2X3 positive feedback loop.


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