Eosinophil Production of PGD2 in Aspirin-Exacerbated Respiratory Disease

Rationale: Aspirin-exacerbated respiratory disease (AERD) differs from aspirin tolerant disease in part due to high tissue eosinophilic infiltration and the over-expression of arachidonic acid metabolic pathway components driving secretion of cysteinyl leukotrienes (CysLT) and prostaglandin D₂ (PGD₂).  We had previously shown the capacity of interferon (IFN)-γ to drive CysLT expression pathways.  We investigated eosinophils as a source for PGD₂ production in AERD and the ability of (IFN)-γ to drive expression.

Methods: Eosinophils were enriched from tissue and peripheral blood obtained from control, aspirin-tolerant, and AERD subjects.  mRNA was extracted and evaluated for expression of  hematopoietic PGD synthase (hPGDS).  Expression of hPGDS protein was confirmed with western blot and immunohistochemical staining.  Cells were stimulated with aspirin and secretion of PGD₂ quantified.  Finally, CD34⁺ progenitor cells were isolated and matured into eosinophils in the presence or absence of IFN-γ and hPGDS mRNA and PGD₂ release measured.

Results: Gene expression analysis revealed that eosinophils from AERD tissue and blood display increased levels of hPGDS compared with asthmatic and control samples.  Western blot confirmed the increase in hPGDS gene expression translated to increased protein expression.  Using immunofluorescence, mast cells and eosinophils from AERD and asthmatic subjects demonstrated hPGDS with higher levels in AERD eosinophils.  Incubation of eosinophils from blood and tissue with aspirin stimulated PGD₂ release.  IFN-γ-matured eosinophil progenitors showed enhanced hPGDS expression and increased levels of PGD₂ release at baseline and following stimulation with aspirin. 

Conclusions: In addition to mast cells, eosinophils represent an important source of PGD₂ in AERD at baseline and following exposure to aspirin.