BONE-MARROW CONTRIBUTION TO EOSINOPHILIC INFLAMMATION

Allergen-induced bone marrow responses are observable in human allergi c asthmatics, involving specific increases in eosinophil-basophil prog enitors (Eo/B-CFU), measured either by hemopoietic assays or by flow c ytometric analyses of CD34-positive, IL-3R alpha-positive, and/or IL-5 -responsive cell populations. The results are consistent with the upre gulation of an IL-5-sensitive population of progenitors in allergen-in duced late phase asthmatic responses. Studies in vitro on the phenotyp e of developing eosinophils and basophils suggest that the early acqui sition of IL-5R alpha, as well as the capacity to produce cytokines su ch as GM-CSF and IL-5, are features of the differentiation process. Th ese observations are consistent with findings in animal models, indica ting that allergen-induced increases in bone marrow progenitor formati on depend on hemopoietic factor(s) released post-allergen. The possibi lity that there is constitutive marrow upregulation of eosinophilopoie sis in allergic airways disease is also an area for Suture investigati on.