Eosinophils do not enhance the trans-basement-membrane migration of neutrophils

There is increasing evidence that both neutrophilic and eosinophilic inflammation persist in the airways of patients with severe asthma. We have reported a positive relationship between the concentrations of eosinophils and neutrophils in sputum from severe asthmatics, suggesting a possible role of eosinophils in regulating neutrophilic inflammation. The aim of this study was to investigate whether activated eosinophils modify the trans-basement membrane migration (TBM) of neutrophils.

Eosinophils and neutrophils were isolated from peripheral blood drawn from healthy donors. The TBM of neutrophils in response to a variety of chemoattractants was evaluated in the presence or absence of eosinophils by using the chambers with a Matrigel-coated Transwell insert.

As expected, eotaxin (10 nM) and RANTES (10 nM), but not IL-8 (10 nM), induced the TBM of eosinophils. On the contrary, only IL-8 induced the TBM of neutrophils. When eosinophils were coincubated with neutrophils and stimulated with IL-8, the TBM of eosinophils was significantly augmented. On the other hand, when neutrophils were coincubated with eosinophils and stimulated with eotaxin or RANTES, the TBM of neutrophils was not modified.

Neutrophils migrated by IL-8 may lead eosinophils to accumulate in the airways of patients with severe asthma. On the other hand, it is unlikely that eosinophils migrated by chemoattractants such as CC chemokines regulate neutrophilic inflammation.