Relationship of in vitro survival and eosinophil derived neurotoxin (EDN) degranulation in blood and airway eosinophils (EOS) following segmental bronchoprovocation with allergen (SBP-AG)

Abstract

Rationale EOS isolated from blood and bronchoalveolar lavage fluid (BAL) 48h post-SBP-AG of allergic asthmatic (AA) patients differ in function. Although both populations of EOS have increased in vitro survival, only airway cells have enhanced respiratory burst, adhesion and intracellular calcium flux. We hypothesized that increased EOS survival results in enhanced retention of these cells in the airways in asthma to thus promote airway inflammation. Methods To correlate functional changes based on cell compartmentalization, blood and BAL EOS were isolated from AA subjects 48h post-SBP-AG; in vitro survival (trypan blue exclusion) and EDN degranulation (RIA) were assessed in response to IL-5 or GM-CSF. Results In contrast to increased survival of both cell populations, BAL EOS had significantly reduced IL-5 and GM-CSF activated EDN degranulation compared with blood EOS. Peripheral blood EOS demonstrated a significant correlation between spontaneous, and IL-5- or GM-CSF-stimulated EDN degranulation (rs=0.7-1.0, p<0.05, n=5) but not in vitro survival. In contrast, BAL EOS had a strong correlation between unstimulated, IL-5- and GM-CSF-enhanced survival (rs=0.5-1.0, p<0.05, n=5) but not EDN degranulation. In both blood and BAL EOS, increased spontaneous in vitro survival tended to inversely correlate with IL-5-stimulated EDN degranulation (Rs<−0.80, p=0.083, n=5). This did not appear to be due to in vivo degranulation since intracellular EDN concentrations in blood and BAL EOS were similar to circulating EOS from unchallenged AA subjects. Conclusion These data suggest enhanced survival of circulating and airway EOS following AG challenge is not necessarily associated with increased cell function and these two processes are regulated differently.