Background: Eosinophils develop from bone marrow (BM) progenitors, and interleukin-5 (IL-5) and eotaxin may act in expansion and mobilisation of BM eosinophils in asthma.
Methods: We have examined phenotypic changes as CD34+ cells develop to the eosinophil lineage in vitro, and have evaluated BM eosinophils from asthmatic and control subjects for expression of the eotaxin receptor, CCR3.
Results: Acquisition of receptors for IL-5 and CCR3 was an early event in eosinophil development. There were increased CD34+ cells, and mature and immature CCR3+ eosinophils in BM from asthmatics.
Conclusion: These data suggest that IL-5 may act early in eosinophil development, and that eotaxin has the capacity to mobilise a BM eosinophil pool in asthma.